Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 4558 insertions, 0 deletions

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
new file mode 100644
index 000000000..1672d4846
--- /dev/null
+++ b/fs/btrfs/scrub.c
@@ -0,0 +1,4558 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2011, 2012 STRATO.  All rights reserved.
+ */
+
+#include <linux/blkdev.h>
+#include <linux/ratelimit.h>
+#include <linux/sched/mm.h>
+#include <crypto/hash.h>
+#include "ctree.h"
+#include "discard.h"
+#include "volumes.h"
+#include "disk-io.h"
+#include "ordered-data.h"
+#include "transaction.h"
+#include "backref.h"
+#include "extent_io.h"
+#include "dev-replace.h"
+#include "check-integrity.h"
+#include "rcu-string.h"
+#include "raid56.h"
+#include "block-group.h"
+#include "zoned.h"
+
+/*
+ * This is only the first step towards a full-features scrub. It reads all
+ * extent and super block and verifies the checksums. In case a bad checksum
+ * is found or the extent cannot be read, good data will be written back if
+ * any can be found.
+ *
+ * Future enhancements:
+ *  - In case an unrepairable extent is encountered, track which files are
+ *    affected and report them
+ *  - track and record media errors, throw out bad devices
+ *  - add a mode to also read unallocated space
+ */
+
+struct scrub_block;
+struct scrub_ctx;
+
+/*
+ * The following three values only influence the performance.
+ *
+ * The last one configures the number of parallel and outstanding I/O
+ * operations. The first one configures an upper limit for the number
+ * of (dynamically allocated) pages that are added to a bio.
+ */
+#define SCRUB_SECTORS_PER_BIO	32	/* 128KiB per bio for 4KiB pages */
+#define SCRUB_BIOS_PER_SCTX	64	/* 8MiB per device in flight for 4KiB pages */
+
+/*
+ * The following value times PAGE_SIZE needs to be large enough to match the
+ * largest node/leaf/sector size that shall be supported.
+ */
+#define SCRUB_MAX_SECTORS_PER_BLOCK	(BTRFS_MAX_METADATA_BLOCKSIZE / SZ_4K)
+
+#define SCRUB_MAX_PAGES			(DIV_ROUND_UP(BTRFS_MAX_METADATA_BLOCKSIZE, PAGE_SIZE))
+
+struct scrub_recover {
+	refcount_t		refs;
+	struct btrfs_io_context	*bioc;
+	u64			map_length;
+};
+
+struct scrub_sector {
+	struct scrub_block	*sblock;
+	struct list_head	list;
+	u64			flags;  /* extent flags */
+	u64			generation;
+	/* Offset in bytes to @sblock. */
+	u32			offset;
+	atomic_t		refs;
+	unsigned int		have_csum:1;
+	unsigned int		io_error:1;
+	u8			csum[BTRFS_CSUM_SIZE];
+
+	struct scrub_recover	*recover;
+};
+
+struct scrub_bio {
+	int			index;
+	struct scrub_ctx	*sctx;
+	struct btrfs_device	*dev;
+	struct bio		*bio;
+	blk_status_t		status;
+	u64			logical;
+	u64			physical;
+	struct scrub_sector	*sectors[SCRUB_SECTORS_PER_BIO];
+	int			sector_count;
+	int			next_free;
+	struct work_struct	work;
+};
+
+struct scrub_block {
+	/*
+	 * Each page will have its page::private used to record the logical
+	 * bytenr.
+	 */
+	struct page		*pages[SCRUB_MAX_PAGES];
+	struct scrub_sector	*sectors[SCRUB_MAX_SECTORS_PER_BLOCK];
+	struct btrfs_device	*dev;
+	/* Logical bytenr of the sblock */
+	u64			logical;
+	u64			physical;
+	u64			physical_for_dev_replace;
+	/* Length of sblock in bytes */
+	u32			len;
+	int			sector_count;
+	int			mirror_num;
+
+	atomic_t		outstanding_sectors;
+	refcount_t		refs; /* free mem on transition to zero */
+	struct scrub_ctx	*sctx;
+	struct scrub_parity	*sparity;
+	struct {
+		unsigned int	header_error:1;
+		unsigned int	checksum_error:1;
+		unsigned int	no_io_error_seen:1;
+		unsigned int	generation_error:1; /* also sets header_error */
+
+		/* The following is for the data used to check parity */
+		/* It is for the data with checksum */
+		unsigned int	data_corrected:1;
+	};
+	struct work_struct	work;
+};
+
+/* Used for the chunks with parity stripe such RAID5/6 */
+struct scrub_parity {
+	struct scrub_ctx	*sctx;
+
+	struct btrfs_device	*scrub_dev;
+
+	u64			logic_start;
+
+	u64			logic_end;
+
+	int			nsectors;
+
+	u32			stripe_len;
+
+	refcount_t		refs;
+
+	struct list_head	sectors_list;
+
+	/* Work of parity check and repair */
+	struct work_struct	work;
+
+	/* Mark the parity blocks which have data */
+	unsigned long		dbitmap;
+
+	/*
+	 * Mark the parity blocks which have data, but errors happen when
+	 * read data or check data
+	 */
+	unsigned long		ebitmap;
+};
+
+struct scrub_ctx {
+	struct scrub_bio	*bios[SCRUB_BIOS_PER_SCTX];
+	struct btrfs_fs_info	*fs_info;
+	int			first_free;
+	int			curr;
+	atomic_t		bios_in_flight;
+	atomic_t		workers_pending;
+	spinlock_t		list_lock;
+	wait_queue_head_t	list_wait;
+	struct list_head	csum_list;
+	atomic_t		cancel_req;
+	int			readonly;
+	int			sectors_per_bio;
+
+	/* State of IO submission throttling affecting the associated device */
+	ktime_t			throttle_deadline;
+	u64			throttle_sent;
+
+	int			is_dev_replace;
+	u64			write_pointer;
+
+	struct scrub_bio        *wr_curr_bio;
+	struct mutex            wr_lock;
+	struct btrfs_device     *wr_tgtdev;
+	bool                    flush_all_writes;
+
+	/*
+	 * statistics
+	 */
+	struct btrfs_scrub_progress stat;
+	spinlock_t		stat_lock;
+
+	/*
+	 * Use a ref counter to avoid use-after-free issues. Scrub workers
+	 * decrement bios_in_flight and workers_pending and then do a wakeup
+	 * on the list_wait wait queue. We must ensure the main scrub task
+	 * doesn't free the scrub context before or while the workers are
+	 * doing the wakeup() call.
+	 */
+	refcount_t              refs;
+};
+
+struct scrub_warning {
+	struct btrfs_path	*path;
+	u64			extent_item_size;
+	const char		*errstr;
+	u64			physical;
+	u64			logical;
+	struct btrfs_device	*dev;
+};
+
+struct full_stripe_lock {
+	struct rb_node node;
+	u64 logical;
+	u64 refs;
+	struct mutex mutex;
+};
+
+#ifndef CONFIG_64BIT
+/* This structure is for archtectures whose (void *) is smaller than u64 */
+struct scrub_page_private {
+	u64 logical;
+};
+#endif
+
+static int attach_scrub_page_private(struct page *page, u64 logical)
+{
+#ifdef CONFIG_64BIT
+	attach_page_private(page, (void *)logical);
+	return 0;
+#else
+	struct scrub_page_private *spp;
+
+	spp = kmalloc(sizeof(*spp), GFP_KERNEL);
+	if (!spp)
+		return -ENOMEM;
+	spp->logical = logical;
+	attach_page_private(page, (void *)spp);
+	return 0;
+#endif
+}
+
+static void detach_scrub_page_private(struct page *page)
+{
+#ifdef CONFIG_64BIT
+	detach_page_private(page);
+	return;
+#else
+	struct scrub_page_private *spp;
+
+	spp = detach_page_private(page);
+	kfree(spp);
+	return;
+#endif
+}
+
+static struct scrub_block *alloc_scrub_block(struct scrub_ctx *sctx,
+					     struct btrfs_device *dev,
+					     u64 logical, u64 physical,
+					     u64 physical_for_dev_replace,
+					     int mirror_num)
+{
+	struct scrub_block *sblock;
+
+	sblock = kzalloc(sizeof(*sblock), GFP_KERNEL);
+	if (!sblock)
+		return NULL;
+	refcount_set(&sblock->refs, 1);
+	sblock->sctx = sctx;
+	sblock->logical = logical;
+	sblock->physical = physical;
+	sblock->physical_for_dev_replace = physical_for_dev_replace;
+	sblock->dev = dev;
+	sblock->mirror_num = mirror_num;
+	sblock->no_io_error_seen = 1;
+	/*
+	 * Scrub_block::pages will be allocated at alloc_scrub_sector() when
+	 * the corresponding page is not allocated.
+	 */
+	return sblock;
+}
+
+/*
+ * Allocate a new scrub sector and attach it to @sblock.
+ *
+ * Will also allocate new pages for @sblock if needed.
+ */
+static struct scrub_sector *alloc_scrub_sector(struct scrub_block *sblock,
+					       u64 logical, gfp_t gfp)
+{
+	const pgoff_t page_index = (logical - sblock->logical) >> PAGE_SHIFT;
+	struct scrub_sector *ssector;
+
+	/* We must never have scrub_block exceed U32_MAX in size. */
+	ASSERT(logical - sblock->logical < U32_MAX);
+
+	ssector = kzalloc(sizeof(*ssector), gfp);
+	if (!ssector)
+		return NULL;
+
+	/* Allocate a new page if the slot is not allocated */
+	if (!sblock->pages[page_index]) {
+		int ret;
+
+		sblock->pages[page_index] = alloc_page(gfp);
+		if (!sblock->pages[page_index]) {
+			kfree(ssector);
+			return NULL;
+		}
+		ret = attach_scrub_page_private(sblock->pages[page_index],
+				sblock->logical + (page_index << PAGE_SHIFT));
+		if (ret < 0) {
+			kfree(ssector);
+			__free_page(sblock->pages[page_index]);
+			sblock->pages[page_index] = NULL;
+			return NULL;
+		}
+	}
+
+	atomic_set(&ssector->refs, 1);
+	ssector->sblock = sblock;
+	/* The sector to be added should not be used */
+	ASSERT(sblock->sectors[sblock->sector_count] == NULL);
+	ssector->offset = logical - sblock->logical;
+
+	/* The sector count must be smaller than the limit */
+	ASSERT(sblock->sector_count < SCRUB_MAX_SECTORS_PER_BLOCK);
+
+	sblock->sectors[sblock->sector_count] = ssector;
+	sblock->sector_count++;
+	sblock->len += sblock->sctx->fs_info->sectorsize;
+
+	return ssector;
+}
+
+static struct page *scrub_sector_get_page(struct scrub_sector *ssector)
+{
+	struct scrub_block *sblock = ssector->sblock;
+	pgoff_t index;
+	/*
+	 * When calling this function, ssector must be alreaday attached to the
+	 * parent sblock.
+	 */
+	ASSERT(sblock);
+
+	/* The range should be inside the sblock range */
+	ASSERT(ssector->offset < sblock->len);
+
+	index = ssector->offset >> PAGE_SHIFT;
+	ASSERT(index < SCRUB_MAX_PAGES);
+	ASSERT(sblock->pages[index]);
+	ASSERT(PagePrivate(sblock->pages[index]));
+	return sblock->pages[index];
+}
+
+static unsigned int scrub_sector_get_page_offset(struct scrub_sector *ssector)
+{
+	struct scrub_block *sblock = ssector->sblock;
+
+	/*
+	 * When calling this function, ssector must be already attached to the
+	 * parent sblock.
+	 */
+	ASSERT(sblock);
+
+	/* The range should be inside the sblock range */
+	ASSERT(ssector->offset < sblock->len);
+
+	return offset_in_page(ssector->offset);
+}
+
+static char *scrub_sector_get_kaddr(struct scrub_sector *ssector)
+{
+	return page_address(scrub_sector_get_page(ssector)) +
+	       scrub_sector_get_page_offset(ssector);
+}
+
+static int bio_add_scrub_sector(struct bio *bio, struct scrub_sector *ssector,
+				unsigned int len)
+{
+	return bio_add_page(bio, scrub_sector_get_page(ssector), len,
+			    scrub_sector_get_page_offset(ssector));
+}
+
+static int scrub_setup_recheck_block(struct scrub_block *original_sblock,
+				     struct scrub_block *sblocks_for_recheck[]);
+static void scrub_recheck_block(struct btrfs_fs_info *fs_info,
+				struct scrub_block *sblock,
+				int retry_failed_mirror);
+static void scrub_recheck_block_checksum(struct scrub_block *sblock);
+static int scrub_repair_block_from_good_copy(struct scrub_block *sblock_bad,
+					     struct scrub_block *sblock_good);
+static int scrub_repair_sector_from_good_copy(struct scrub_block *sblock_bad,
+					    struct scrub_block *sblock_good,
+					    int sector_num, int force_write);
+static void scrub_write_block_to_dev_replace(struct scrub_block *sblock);
+static int scrub_write_sector_to_dev_replace(struct scrub_block *sblock,
+					     int sector_num);
+static int scrub_checksum_data(struct scrub_block *sblock);
+static int scrub_checksum_tree_block(struct scrub_block *sblock);
+static int scrub_checksum_super(struct scrub_block *sblock);
+static void scrub_block_put(struct scrub_block *sblock);
+static void scrub_sector_get(struct scrub_sector *sector);
+static void scrub_sector_put(struct scrub_sector *sector);
+static void scrub_parity_get(struct scrub_parity *sparity);
+static void scrub_parity_put(struct scrub_parity *sparity);
+static int scrub_sectors(struct scrub_ctx *sctx, u64 logical, u32 len,
+			 u64 physical, struct btrfs_device *dev, u64 flags,
+			 u64 gen, int mirror_num, u8 *csum,
+			 u64 physical_for_dev_replace);
+static void scrub_bio_end_io(struct bio *bio);
+static void scrub_bio_end_io_worker(struct work_struct *work);
+static void scrub_block_complete(struct scrub_block *sblock);
+static void scrub_find_good_copy(struct btrfs_fs_info *fs_info,
+				 u64 extent_logical, u32 extent_len,
+				 u64 *extent_physical,
+				 struct btrfs_device **extent_dev,
+				 int *extent_mirror_num);
+static int scrub_add_sector_to_wr_bio(struct scrub_ctx *sctx,
+				      struct scrub_sector *sector);
+static void scrub_wr_submit(struct scrub_ctx *sctx);
+static void scrub_wr_bio_end_io(struct bio *bio);
+static void scrub_wr_bio_end_io_worker(struct work_struct *work);
+static void scrub_put_ctx(struct scrub_ctx *sctx);
+
+static inline int scrub_is_page_on_raid56(struct scrub_sector *sector)
+{
+	return sector->recover &&
+	       (sector->recover->bioc->map_type & BTRFS_BLOCK_GROUP_RAID56_MASK);
+}
+
+static void scrub_pending_bio_inc(struct scrub_ctx *sctx)
+{
+	refcount_inc(&sctx->refs);
+	atomic_inc(&sctx->bios_in_flight);
+}
+
+static void scrub_pending_bio_dec(struct scrub_ctx *sctx)
+{
+	atomic_dec(&sctx->bios_in_flight);
+	wake_up(&sctx->list_wait);
+	scrub_put_ctx(sctx);
+}
+
+static void __scrub_blocked_if_needed(struct btrfs_fs_info *fs_info)
+{
+	while (atomic_read(&fs_info->scrub_pause_req)) {
+		mutex_unlock(&fs_info->scrub_lock);
+		wait_event(fs_info->scrub_pause_wait,
+		   atomic_read(&fs_info->scrub_pause_req) == 0);
+		mutex_lock(&fs_info->scrub_lock);
+	}
+}
+
+static void scrub_pause_on(struct btrfs_fs_info *fs_info)
+{
+	atomic_inc(&fs_info->scrubs_paused);
+	wake_up(&fs_info->scrub_pause_wait);
+}
+
+static void scrub_pause_off(struct btrfs_fs_info *fs_info)
+{
+	mutex_lock(&fs_info->scrub_lock);
+	__scrub_blocked_if_needed(fs_info);
+	atomic_dec(&fs_info->scrubs_paused);
+	mutex_unlock(&fs_info->scrub_lock);
+
+	wake_up(&fs_info->scrub_pause_wait);
+}
+
+static void scrub_blocked_if_needed(struct btrfs_fs_info *fs_info)
+{
+	scrub_pause_on(fs_info);
+	scrub_pause_off(fs_info);
+}
+
+/*
+ * Insert new full stripe lock into full stripe locks tree
+ *
+ * Return pointer to existing or newly inserted full_stripe_lock structure if
+ * everything works well.
+ * Return ERR_PTR(-ENOMEM) if we failed to allocate memory
+ *
+ * NOTE: caller must hold full_stripe_locks_root->lock before calling this
+ * function
+ */
+static struct full_stripe_lock *insert_full_stripe_lock(
+		struct btrfs_full_stripe_locks_tree *locks_root,
+		u64 fstripe_logical)
+{
+	struct rb_node **p;
+	struct rb_node *parent = NULL;
+	struct full_stripe_lock *entry;
+	struct full_stripe_lock *ret;
+
+	lockdep_assert_held(&locks_root->lock);
+
+	p = &locks_root->root.rb_node;
+	while (*p) {
+		parent = *p;
+		entry = rb_entry(parent, struct full_stripe_lock, node);
+		if (fstripe_logical < entry->logical) {
+			p = &(*p)->rb_left;
+		} else if (fstripe_logical > entry->logical) {
+			p = &(*p)->rb_right;
+		} else {
+			entry->refs++;
+			return entry;
+		}
+	}
+
+	/*
+	 * Insert new lock.
+	 */
+	ret = kmalloc(sizeof(*ret), GFP_KERNEL);
+	if (!ret)
+		return ERR_PTR(-ENOMEM);
+	ret->logical = fstripe_logical;
+	ret->refs = 1;
+	mutex_init(&ret->mutex);
+
+	rb_link_node(&ret->node, parent, p);
+	rb_insert_color(&ret->node, &locks_root->root);
+	return ret;
+}
+
+/*
+ * Search for a full stripe lock of a block group
+ *
+ * Return pointer to existing full stripe lock if found
+ * Return NULL if not found
+ */
+static struct full_stripe_lock *search_full_stripe_lock(
+		struct btrfs_full_stripe_locks_tree *locks_root,
+		u64 fstripe_logical)
+{
+	struct rb_node *node;
+	struct full_stripe_lock *entry;
+
+	lockdep_assert_held(&locks_root->lock);
+
+	node = locks_root->root.rb_node;
+	while (node) {
+		entry = rb_entry(node, struct full_stripe_lock, node);
+		if (fstripe_logical < entry->logical)
+			node = node->rb_left;
+		else if (fstripe_logical > entry->logical)
+			node = node->rb_right;
+		else
+			return entry;
+	}
+	return NULL;
+}
+
+/*
+ * Helper to get full stripe logical from a normal bytenr.
+ *
+ * Caller must ensure @cache is a RAID56 block group.
+ */
+static u64 get_full_stripe_logical(struct btrfs_block_group *cache, u64 bytenr)
+{
+	u64 ret;
+
+	/*
+	 * Due to chunk item size limit, full stripe length should not be
+	 * larger than U32_MAX. Just a sanity check here.
+	 */
+	WARN_ON_ONCE(cache->full_stripe_len >= U32_MAX);
+
+	/*
+	 * round_down() can only handle power of 2, while RAID56 full
+	 * stripe length can be 64KiB * n, so we need to manually round down.
+	 */
+	ret = div64_u64(bytenr - cache->start, cache->full_stripe_len) *
+			cache->full_stripe_len + cache->start;
+	return ret;
+}
+
+/*
+ * Lock a full stripe to avoid concurrency of recovery and read
+ *
+ * It's only used for profiles with parities (RAID5/6), for other profiles it
+ * does nothing.
+ *
+ * Return 0 if we locked full stripe covering @bytenr, with a mutex held.
+ * So caller must call unlock_full_stripe() at the same context.
+ *
+ * Return <0 if encounters error.
+ */
+static int lock_full_stripe(struct btrfs_fs_info *fs_info, u64 bytenr,
+			    bool *locked_ret)
+{
+	struct btrfs_block_group *bg_cache;
+	struct btrfs_full_stripe_locks_tree *locks_root;
+	struct full_stripe_lock *existing;
+	u64 fstripe_start;
+	int ret = 0;
+
+	*locked_ret = false;
+	bg_cache = btrfs_lookup_block_group(fs_info, bytenr);
+	if (!bg_cache) {
+		ASSERT(0);
+		return -ENOENT;
+	}
+
+	/* Profiles not based on parity don't need full stripe lock */
+	if (!(bg_cache->flags & BTRFS_BLOCK_GROUP_RAID56_MASK))
+		goto out;
+	locks_root = &bg_cache->full_stripe_locks_root;
+
+	fstripe_start = get_full_stripe_logical(bg_cache, bytenr);
+
+	/* Now insert the full stripe lock */
+	mutex_lock(&locks_root->lock);
+	existing = insert_full_stripe_lock(locks_root, fstripe_start);
+	mutex_unlock(&locks_root->lock);
+	if (IS_ERR(existing)) {
+		ret = PTR_ERR(existing);
+		goto out;
+	}
+	mutex_lock(&existing->mutex);
+	*locked_ret = true;
+out:
+	btrfs_put_block_group(bg_cache);
+	return ret;
+}
+
+/*
+ * Unlock a full stripe.
+ *
+ * NOTE: Caller must ensure it's the same context calling corresponding
+ * lock_full_stripe().
+ *
+ * Return 0 if we unlock full stripe without problem.
+ * Return <0 for error
+ */
+static int unlock_full_stripe(struct btrfs_fs_info *fs_info, u64 bytenr,
+			      bool locked)
+{
+	struct btrfs_block_group *bg_cache;
+	struct btrfs_full_stripe_locks_tree *locks_root;
+	struct full_stripe_lock *fstripe_lock;
+	u64 fstripe_start;
+	bool freeit = false;
+	int ret = 0;
+
+	/* If we didn't acquire full stripe lock, no need to continue */
+	if (!locked)
+		return 0;
+
+	bg_cache = btrfs_lookup_block_group(fs_info, bytenr);
+	if (!bg_cache) {
+		ASSERT(0);
+		return -ENOENT;
+	}
+	if (!(bg_cache->flags & BTRFS_BLOCK_GROUP_RAID56_MASK))
+		goto out;
+
+	locks_root = &bg_cache->full_stripe_locks_root;
+	fstripe_start = get_full_stripe_logical(bg_cache, bytenr);
+
+	mutex_lock(&locks_root->lock);
+	fstripe_lock = search_full_stripe_lock(locks_root, fstripe_start);
+	/* Unpaired unlock_full_stripe() detected */
+	if (!fstripe_lock) {
+		WARN_ON(1);
+		ret = -ENOENT;
+		mutex_unlock(&locks_root->lock);
+		goto out;
+	}
+
+	if (fstripe_lock->refs == 0) {
+		WARN_ON(1);
+		btrfs_warn(fs_info, "full stripe lock at %llu refcount underflow",
+			fstripe_lock->logical);
+	} else {
+		fstripe_lock->refs--;
+	}
+
+	if (fstripe_lock->refs == 0) {
+		rb_erase(&fstripe_lock->node, &locks_root->root);
+		freeit = true;
+	}
+	mutex_unlock(&locks_root->lock);
+
+	mutex_unlock(&fstripe_lock->mutex);
+	if (freeit)
+		kfree(fstripe_lock);
+out:
+	btrfs_put_block_group(bg_cache);
+	return ret;
+}
+
+static void scrub_free_csums(struct scrub_ctx *sctx)
+{
+	while (!list_empty(&sctx->csum_list)) {
+		struct btrfs_ordered_sum *sum;
+		sum = list_first_entry(&sctx->csum_list,
+				       struct btrfs_ordered_sum, list);
+		list_del(&sum->list);
+		kfree(sum);
+	}
+}
+
+static noinline_for_stack void scrub_free_ctx(struct scrub_ctx *sctx)
+{
+	int i;
+
+	if (!sctx)
+		return;
+
+	/* this can happen when scrub is cancelled */
+	if (sctx->curr != -1) {
+		struct scrub_bio *sbio = sctx->bios[sctx->curr];
+
+		for (i = 0; i < sbio->sector_count; i++)
+			scrub_block_put(sbio->sectors[i]->sblock);
+		bio_put(sbio->bio);
+	}
+
+	for (i = 0; i < SCRUB_BIOS_PER_SCTX; ++i) {
+		struct scrub_bio *sbio = sctx->bios[i];
+
+		if (!sbio)
+			break;
+		kfree(sbio);
+	}
+
+	kfree(sctx->wr_curr_bio);
+	scrub_free_csums(sctx);
+	kfree(sctx);
+}
+
+static void scrub_put_ctx(struct scrub_ctx *sctx)
+{
+	if (refcount_dec_and_test(&sctx->refs))
+		scrub_free_ctx(sctx);
+}
+
+static noinline_for_stack struct scrub_ctx *scrub_setup_ctx(
+		struct btrfs_fs_info *fs_info, int is_dev_replace)
+{
+	struct scrub_ctx *sctx;
+	int		i;
+
+	sctx = kzalloc(sizeof(*sctx), GFP_KERNEL);
+	if (!sctx)
+		goto nomem;
+	refcount_set(&sctx->refs, 1);
+	sctx->is_dev_replace = is_dev_replace;
+	sctx->sectors_per_bio = SCRUB_SECTORS_PER_BIO;
+	sctx->curr = -1;
+	sctx->fs_info = fs_info;
+	INIT_LIST_HEAD(&sctx->csum_list);
+	for (i = 0; i < SCRUB_BIOS_PER_SCTX; ++i) {
+		struct scrub_bio *sbio;
+
+		sbio = kzalloc(sizeof(*sbio), GFP_KERNEL);
+		if (!sbio)
+			goto nomem;
+		sctx->bios[i] = sbio;
+
+		sbio->index = i;
+		sbio->sctx = sctx;
+		sbio->sector_count = 0;
+		INIT_WORK(&sbio->work, scrub_bio_end_io_worker);
+
+		if (i != SCRUB_BIOS_PER_SCTX - 1)
+			sctx->bios[i]->next_free = i + 1;
+		else
+			sctx->bios[i]->next_free = -1;
+	}
+	sctx->first_free = 0;
+	atomic_set(&sctx->bios_in_flight, 0);
+	atomic_set(&sctx->workers_pending, 0);
+	atomic_set(&sctx->cancel_req, 0);
+
+	spin_lock_init(&sctx->list_lock);
+	spin_lock_init(&sctx->stat_lock);
+	init_waitqueue_head(&sctx->list_wait);
+	sctx->throttle_deadline = 0;
+
+	WARN_ON(sctx->wr_curr_bio != NULL);
+	mutex_init(&sctx->wr_lock);
+	sctx->wr_curr_bio = NULL;
+	if (is_dev_replace) {
+		WARN_ON(!fs_info->dev_replace.tgtdev);
+		sctx->wr_tgtdev = fs_info->dev_replace.tgtdev;
+		sctx->flush_all_writes = false;
+	}
+
+	return sctx;
+
+nomem:
+	scrub_free_ctx(sctx);
+	return ERR_PTR(-ENOMEM);
+}
+
+static int scrub_print_warning_inode(u64 inum, u64 offset, u64 root,
+				     void *warn_ctx)
+{
+	u32 nlink;
+	int ret;
+	int i;
+	unsigned nofs_flag;
+	struct extent_buffer *eb;
+	struct btrfs_inode_item *inode_item;
+	struct scrub_warning *swarn = warn_ctx;
+	struct btrfs_fs_info *fs_info = swarn->dev->fs_info;
+	struct inode_fs_paths *ipath = NULL;
+	struct btrfs_root *local_root;
+	struct btrfs_key key;
+
+	local_root = btrfs_get_fs_root(fs_info, root, true);
+	if (IS_ERR(local_root)) {
+		ret = PTR_ERR(local_root);
+		goto err;
+	}
+
+	/*
+	 * this makes the path point to (inum INODE_ITEM ioff)
+	 */
+	key.objectid = inum;
+	key.type = BTRFS_INODE_ITEM_KEY;
+	key.offset = 0;
+
+	ret = btrfs_search_slot(NULL, local_root, &key, swarn->path, 0, 0);
+	if (ret) {
+		btrfs_put_root(local_root);
+		btrfs_release_path(swarn->path);
+		goto err;
+	}
+
+	eb = swarn->path->nodes[0];
+	inode_item = btrfs_item_ptr(eb, swarn->path->slots[0],
+					struct btrfs_inode_item);
+	nlink = btrfs_inode_nlink(eb, inode_item);
+	btrfs_release_path(swarn->path);
+
+	/*
+	 * init_path might indirectly call vmalloc, or use GFP_KERNEL. Scrub
+	 * uses GFP_NOFS in this context, so we keep it consistent but it does
+	 * not seem to be strictly necessary.
+	 */
+	nofs_flag = memalloc_nofs_save();
+	ipath = init_ipath(4096, local_root, swarn->path);
+	memalloc_nofs_restore(nofs_flag);
+	if (IS_ERR(ipath)) {
+		btrfs_put_root(local_root);
+		ret = PTR_ERR(ipath);
+		ipath = NULL;
+		goto err;
+	}
+	ret = paths_from_inode(inum, ipath);
+
+	if (ret < 0)
+		goto err;
+
+	/*
+	 * we deliberately ignore the bit ipath might have been too small to
+	 * hold all of the paths here
+	 */
+	for (i = 0; i < ipath->fspath->elem_cnt; ++i)
+		btrfs_warn_in_rcu(fs_info,
+"%s at logical %llu on dev %s, physical %llu, root %llu, inode %llu, offset %llu, length %u, links %u (path: %s)",
+				  swarn->errstr, swarn->logical,
+				  rcu_str_deref(swarn->dev->name),
+				  swarn->physical,
+				  root, inum, offset,
+				  fs_info->sectorsize, nlink,
+				  (char *)(unsigned long)ipath->fspath->val[i]);
+
+	btrfs_put_root(local_root);
+	free_ipath(ipath);
+	return 0;
+
+err:
+	btrfs_warn_in_rcu(fs_info,
+			  "%s at logical %llu on dev %s, physical %llu, root %llu, inode %llu, offset %llu: path resolving failed with ret=%d",
+			  swarn->errstr, swarn->logical,
+			  rcu_str_deref(swarn->dev->name),
+			  swarn->physical,
+			  root, inum, offset, ret);
+
+	free_ipath(ipath);
+	return 0;
+}
+
+static void scrub_print_warning(const char *errstr, struct scrub_block *sblock)
+{
+	struct btrfs_device *dev;
+	struct btrfs_fs_info *fs_info;
+	struct btrfs_path *path;
+	struct btrfs_key found_key;
+	struct extent_buffer *eb;
+	struct btrfs_extent_item *ei;
+	struct scrub_warning swarn;
+	unsigned long ptr = 0;
+	u64 extent_item_pos;
+	u64 flags = 0;
+	u64 ref_root;
+	u32 item_size;
+	u8 ref_level = 0;
+	int ret;
+
+	WARN_ON(sblock->sector_count < 1);
+	dev = sblock->dev;
+	fs_info = sblock->sctx->fs_info;
+
+	/* Super block error, no need to search extent tree. */
+	if (sblock->sectors[0]->flags & BTRFS_EXTENT_FLAG_SUPER) {
+		btrfs_warn_in_rcu(fs_info, "%s on device %s, physical %llu",
+			errstr, rcu_str_deref(dev->name),
+			sblock->physical);
+		return;
+	}
+	path = btrfs_alloc_path();
+	if (!path)
+		return;
+
+	swarn.physical = sblock->physical;
+	swarn.logical = sblock->logical;
+	swarn.errstr = errstr;
+	swarn.dev = NULL;
+
+	ret = extent_from_logical(fs_info, swarn.logical, path, &found_key,
+				  &flags);
+	if (ret < 0)
+		goto out;
+
+	extent_item_pos = swarn.logical - found_key.objectid;
+	swarn.extent_item_size = found_key.offset;
+
+	eb = path->nodes[0];
+	ei = btrfs_item_ptr(eb, path->slots[0], struct btrfs_extent_item);
+	item_size = btrfs_item_size(eb, path->slots[0]);
+
+	if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
+		do {
+			ret = tree_backref_for_extent(&ptr, eb, &found_key, ei,
+						      item_size, &ref_root,
+						      &ref_level);
+			btrfs_warn_in_rcu(fs_info,
+"%s at logical %llu on dev %s, physical %llu: metadata %s (level %d) in tree %llu",
+				errstr, swarn.logical,
+				rcu_str_deref(dev->name),
+				swarn.physical,
+				ref_level ? "node" : "leaf",
+				ret < 0 ? -1 : ref_level,
+				ret < 0 ? -1 : ref_root);
+		} while (ret != 1);
+		btrfs_release_path(path);
+	} else {
+		btrfs_release_path(path);
+		swarn.path = path;
+		swarn.dev = dev;
+		iterate_extent_inodes(fs_info, found_key.objectid,
+					extent_item_pos, 1,
+					scrub_print_warning_inode, &swarn, false);
+	}
+
+out:
+	btrfs_free_path(path);
+}
+
+static inline void scrub_get_recover(struct scrub_recover *recover)
+{
+	refcount_inc(&recover->refs);
+}
+
+static inline void scrub_put_recover(struct btrfs_fs_info *fs_info,
+				     struct scrub_recover *recover)
+{
+	if (refcount_dec_and_test(&recover->refs)) {
+		btrfs_bio_counter_dec(fs_info);
+		btrfs_put_bioc(recover->bioc);
+		kfree(recover);
+	}
+}
+
+/*
+ * scrub_handle_errored_block gets called when either verification of the
+ * sectors failed or the bio failed to read, e.g. with EIO. In the latter
+ * case, this function handles all sectors in the bio, even though only one
+ * may be bad.
+ * The goal of this function is to repair the errored block by using the
+ * contents of one of the mirrors.
+ */
+static int scrub_handle_errored_block(struct scrub_block *sblock_to_check)
+{
+	struct scrub_ctx *sctx = sblock_to_check->sctx;
+	struct btrfs_device *dev = sblock_to_check->dev;
+	struct btrfs_fs_info *fs_info;
+	u64 logical;
+	unsigned int failed_mirror_index;
+	unsigned int is_metadata;
+	unsigned int have_csum;
+	/* One scrub_block for each mirror */
+	struct scrub_block *sblocks_for_recheck[BTRFS_MAX_MIRRORS] = { 0 };
+	struct scrub_block *sblock_bad;
+	int ret;
+	int mirror_index;
+	int sector_num;
+	int success;
+	bool full_stripe_locked;
+	unsigned int nofs_flag;
+	static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL,
+				      DEFAULT_RATELIMIT_BURST);
+
+	BUG_ON(sblock_to_check->sector_count < 1);
+	fs_info = sctx->fs_info;
+	if (sblock_to_check->sectors[0]->flags & BTRFS_EXTENT_FLAG_SUPER) {
+		/*
+		 * If we find an error in a super block, we just report it.
+		 * They will get written with the next transaction commit
+		 * anyway
+		 */
+		scrub_print_warning("super block error", sblock_to_check);
+		spin_lock(&sctx->stat_lock);
+		++sctx->stat.super_errors;
+		spin_unlock(&sctx->stat_lock);
+		btrfs_dev_stat_inc_and_print(dev, BTRFS_DEV_STAT_CORRUPTION_ERRS);
+		return 0;
+	}
+	logical = sblock_to_check->logical;
+	ASSERT(sblock_to_check->mirror_num);
+	failed_mirror_index = sblock_to_check->mirror_num - 1;
+	is_metadata = !(sblock_to_check->sectors[0]->flags &
+			BTRFS_EXTENT_FLAG_DATA);
+	have_csum = sblock_to_check->sectors[0]->have_csum;
+
+	if (!sctx->is_dev_replace && btrfs_repair_one_zone(fs_info, logical))
+		return 0;
+
+	/*
+	 * We must use GFP_NOFS because the scrub task might be waiting for a
+	 * worker task executing this function and in turn a transaction commit
+	 * might be waiting the scrub task to pause (which needs to wait for all
+	 * the worker tasks to complete before pausing).
+	 * We do allocations in the workers through insert_full_stripe_lock()
+	 * and scrub_add_sector_to_wr_bio(), which happens down the call chain of
+	 * this function.
+	 */
+	nofs_flag = memalloc_nofs_save();
+	/*
+	 * For RAID5/6, race can happen for a different device scrub thread.
+	 * For data corruption, Parity and Data threads will both try
+	 * to recovery the data.
+	 * Race can lead to doubly added csum error, or even unrecoverable
+	 * error.
+	 */
+	ret = lock_full_stripe(fs_info, logical, &full_stripe_locked);
+	if (ret < 0) {
+		memalloc_nofs_restore(nofs_flag);
+		spin_lock(&sctx->stat_lock);
+		if (ret == -ENOMEM)
+			sctx->stat.malloc_errors++;
+		sctx->stat.read_errors++;
+		sctx->stat.uncorrectable_errors++;
+		spin_unlock(&sctx->stat_lock);
+		return ret;
+	}
+
+	/*
+	 * read all mirrors one after the other. This includes to
+	 * re-read the extent or metadata block that failed (that was
+	 * the cause that this fixup code is called) another time,
+	 * sector by sector this time in order to know which sectors
+	 * caused I/O errors and which ones are good (for all mirrors).
+	 * It is the goal to handle the situation when more than one
+	 * mirror contains I/O errors, but the errors do not
+	 * overlap, i.e. the data can be repaired by selecting the
+	 * sectors from those mirrors without I/O error on the
+	 * particular sectors. One example (with blocks >= 2 * sectorsize)
+	 * would be that mirror #1 has an I/O error on the first sector,
+	 * the second sector is good, and mirror #2 has an I/O error on
+	 * the second sector, but the first sector is good.
+	 * Then the first sector of the first mirror can be repaired by
+	 * taking the first sector of the second mirror, and the
+	 * second sector of the second mirror can be repaired by
+	 * copying the contents of the 2nd sector of the 1st mirror.
+	 * One more note: if the sectors of one mirror contain I/O
+	 * errors, the checksum cannot be verified. In order to get
+	 * the best data for repairing, the first attempt is to find
+	 * a mirror without I/O errors and with a validated checksum.
+	 * Only if this is not possible, the sectors are picked from
+	 * mirrors with I/O errors without considering the checksum.
+	 * If the latter is the case, at the end, the checksum of the
+	 * repaired area is verified in order to correctly maintain
+	 * the statistics.
+	 */
+	for (mirror_index = 0; mirror_index < BTRFS_MAX_MIRRORS; mirror_index++) {
+		/*
+		 * Note: the two members refs and outstanding_sectors are not
+		 * used in the blocks that are used for the recheck procedure.
+		 *
+		 * But alloc_scrub_block() will initialize sblock::ref anyway,
+		 * so we can use scrub_block_put() to clean them up.
+		 *
+		 * And here we don't setup the physical/dev for the sblock yet,
+		 * they will be correctly initialized in scrub_setup_recheck_block().
+		 */
+		sblocks_for_recheck[mirror_index] = alloc_scrub_block(sctx, NULL,
+							logical, 0, 0, mirror_index);
+		if (!sblocks_for_recheck[mirror_index]) {
+			spin_lock(&sctx->stat_lock);
+			sctx->stat.malloc_errors++;
+			sctx->stat.read_errors++;
+			sctx->stat.uncorrectable_errors++;
+			spin_unlock(&sctx->stat_lock);
+			btrfs_dev_stat_inc_and_print(dev, BTRFS_DEV_STAT_READ_ERRS);
+			goto out;
+		}
+	}
+
+	/* Setup the context, map the logical blocks and alloc the sectors */
+	ret = scrub_setup_recheck_block(sblock_to_check, sblocks_for_recheck);
+	if (ret) {
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.read_errors++;
+		sctx->stat.uncorrectable_errors++;
+		spin_unlock(&sctx->stat_lock);
+		btrfs_dev_stat_inc_and_print(dev, BTRFS_DEV_STAT_READ_ERRS);
+		goto out;
+	}
+	BUG_ON(failed_mirror_index >= BTRFS_MAX_MIRRORS);
+	sblock_bad = sblocks_for_recheck[failed_mirror_index];
+
+	/* build and submit the bios for the failed mirror, check checksums */
+	scrub_recheck_block(fs_info, sblock_bad, 1);
+
+	if (!sblock_bad->header_error && !sblock_bad->checksum_error &&
+	    sblock_bad->no_io_error_seen) {
+		/*
+		 * The error disappeared after reading sector by sector, or
+		 * the area was part of a huge bio and other parts of the
+		 * bio caused I/O errors, or the block layer merged several
+		 * read requests into one and the error is caused by a
+		 * different bio (usually one of the two latter cases is
+		 * the cause)
+		 */
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.unverified_errors++;
+		sblock_to_check->data_corrected = 1;
+		spin_unlock(&sctx->stat_lock);
+
+		if (sctx->is_dev_replace)
+			scrub_write_block_to_dev_replace(sblock_bad);
+		goto out;
+	}
+
+	if (!sblock_bad->no_io_error_seen) {
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.read_errors++;
+		spin_unlock(&sctx->stat_lock);
+		if (__ratelimit(&rs))
+			scrub_print_warning("i/o error", sblock_to_check);
+		btrfs_dev_stat_inc_and_print(dev, BTRFS_DEV_STAT_READ_ERRS);
+	} else if (sblock_bad->checksum_error) {
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.csum_errors++;
+		spin_unlock(&sctx->stat_lock);
+		if (__ratelimit(&rs))
+			scrub_print_warning("checksum error", sblock_to_check);
+		btrfs_dev_stat_inc_and_print(dev,
+					     BTRFS_DEV_STAT_CORRUPTION_ERRS);
+	} else if (sblock_bad->header_error) {
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.verify_errors++;
+		spin_unlock(&sctx->stat_lock);
+		if (__ratelimit(&rs))
+			scrub_print_warning("checksum/header error",
+					    sblock_to_check);
+		if (sblock_bad->generation_error)
+			btrfs_dev_stat_inc_and_print(dev,
+				BTRFS_DEV_STAT_GENERATION_ERRS);
+		else
+			btrfs_dev_stat_inc_and_print(dev,
+				BTRFS_DEV_STAT_CORRUPTION_ERRS);
+	}
+
+	if (sctx->readonly) {
+		ASSERT(!sctx->is_dev_replace);
+		goto out;
+	}
+
+	/*
+	 * now build and submit the bios for the other mirrors, check
+	 * checksums.
+	 * First try to pick the mirror which is completely without I/O
+	 * errors and also does not have a checksum error.
+	 * If one is found, and if a checksum is present, the full block
+	 * that is known to contain an error is rewritten. Afterwards
+	 * the block is known to be corrected.
+	 * If a mirror is found which is completely correct, and no
+	 * checksum is present, only those sectors are rewritten that had
+	 * an I/O error in the block to be repaired, since it cannot be
+	 * determined, which copy of the other sectors is better (and it
+	 * could happen otherwise that a correct sector would be
+	 * overwritten by a bad one).
+	 */
+	for (mirror_index = 0; ;mirror_index++) {
+		struct scrub_block *sblock_other;
+
+		if (mirror_index == failed_mirror_index)
+			continue;
+
+		/* raid56's mirror can be more than BTRFS_MAX_MIRRORS */
+		if (!scrub_is_page_on_raid56(sblock_bad->sectors[0])) {
+			if (mirror_index >= BTRFS_MAX_MIRRORS)
+				break;
+			if (!sblocks_for_recheck[mirror_index]->sector_count)
+				break;
+
+			sblock_other = sblocks_for_recheck[mirror_index];
+		} else {
+			struct scrub_recover *r = sblock_bad->sectors[0]->recover;
+			int max_allowed = r->bioc->num_stripes - r->bioc->num_tgtdevs;
+
+			if (mirror_index >= max_allowed)
+				break;
+			if (!sblocks_for_recheck[1]->sector_count)
+				break;
+
+			ASSERT(failed_mirror_index == 0);
+			sblock_other = sblocks_for_recheck[1];
+			sblock_other->mirror_num = 1 + mirror_index;
+		}
+
+		/* build and submit the bios, check checksums */
+		scrub_recheck_block(fs_info, sblock_other, 0);
+
+		if (!sblock_other->header_error &&
+		    !sblock_other->checksum_error &&
+		    sblock_other->no_io_error_seen) {
+			if (sctx->is_dev_replace) {
+				scrub_write_block_to_dev_replace(sblock_other);
+				goto corrected_error;
+			} else {
+				ret = scrub_repair_block_from_good_copy(
+						sblock_bad, sblock_other);
+				if (!ret)
+					goto corrected_error;
+			}
+		}
+	}
+
+	if (sblock_bad->no_io_error_seen && !sctx->is_dev_replace)
+		goto did_not_correct_error;
+
+	/*
+	 * In case of I/O errors in the area that is supposed to be
+	 * repaired, continue by picking good copies of those sectors.
+	 * Select the good sectors from mirrors to rewrite bad sectors from
+	 * the area to fix. Afterwards verify the checksum of the block
+	 * that is supposed to be repaired. This verification step is
+	 * only done for the purpose of statistic counting and for the
+	 * final scrub report, whether errors remain.
+	 * A perfect algorithm could make use of the checksum and try
+	 * all possible combinations of sectors from the different mirrors
+	 * until the checksum verification succeeds. For example, when
+	 * the 2nd sector of mirror #1 faces I/O errors, and the 2nd sector
+	 * of mirror #2 is readable but the final checksum test fails,
+	 * then the 2nd sector of mirror #3 could be tried, whether now
+	 * the final checksum succeeds. But this would be a rare
+	 * exception and is therefore not implemented. At least it is
+	 * avoided that the good copy is overwritten.
+	 * A more useful improvement would be to pick the sectors
+	 * without I/O error based on sector sizes (512 bytes on legacy
+	 * disks) instead of on sectorsize. Then maybe 512 byte of one
+	 * mirror could be repaired by taking 512 byte of a different
+	 * mirror, even if other 512 byte sectors in the same sectorsize
+	 * area are unreadable.
+	 */
+	success = 1;
+	for (sector_num = 0; sector_num < sblock_bad->sector_count;
+	     sector_num++) {
+		struct scrub_sector *sector_bad = sblock_bad->sectors[sector_num];
+		struct scrub_block *sblock_other = NULL;
+
+		/* Skip no-io-error sectors in scrub */
+		if (!sector_bad->io_error && !sctx->is_dev_replace)
+			continue;
+
+		if (scrub_is_page_on_raid56(sblock_bad->sectors[0])) {
+			/*
+			 * In case of dev replace, if raid56 rebuild process
+			 * didn't work out correct data, then copy the content
+			 * in sblock_bad to make sure target device is identical
+			 * to source device, instead of writing garbage data in
+			 * sblock_for_recheck array to target device.
+			 */
+			sblock_other = NULL;
+		} else if (sector_bad->io_error) {
+			/* Try to find no-io-error sector in mirrors */
+			for (mirror_index = 0;
+			     mirror_index < BTRFS_MAX_MIRRORS &&
+			     sblocks_for_recheck[mirror_index]->sector_count > 0;
+			     mirror_index++) {
+				if (!sblocks_for_recheck[mirror_index]->
+				    sectors[sector_num]->io_error) {
+					sblock_other = sblocks_for_recheck[mirror_index];
+					break;
+				}
+			}
+			if (!sblock_other)
+				success = 0;
+		}
+
+		if (sctx->is_dev_replace) {
+			/*
+			 * Did not find a mirror to fetch the sector from.
+			 * scrub_write_sector_to_dev_replace() handles this
+			 * case (sector->io_error), by filling the block with
+			 * zeros before submitting the write request
+			 */
+			if (!sblock_other)
+				sblock_other = sblock_bad;
+
+			if (scrub_write_sector_to_dev_replace(sblock_other,
+							      sector_num) != 0) {
+				atomic64_inc(
+					&fs_info->dev_replace.num_write_errors);
+				success = 0;
+			}
+		} else if (sblock_other) {
+			ret = scrub_repair_sector_from_good_copy(sblock_bad,
+								 sblock_other,
+								 sector_num, 0);
+			if (0 == ret)
+				sector_bad->io_error = 0;
+			else
+				success = 0;
+		}
+	}
+
+	if (success && !sctx->is_dev_replace) {
+		if (is_metadata || have_csum) {
+			/*
+			 * need to verify the checksum now that all
+			 * sectors on disk are repaired (the write
+			 * request for data to be repaired is on its way).
+			 * Just be lazy and use scrub_recheck_block()
+			 * which re-reads the data before the checksum
+			 * is verified, but most likely the data comes out
+			 * of the page cache.
+			 */
+			scrub_recheck_block(fs_info, sblock_bad, 1);
+			if (!sblock_bad->header_error &&
+			    !sblock_bad->checksum_error &&
+			    sblock_bad->no_io_error_seen)
+				goto corrected_error;
+			else
+				goto did_not_correct_error;
+		} else {
+corrected_error:
+			spin_lock(&sctx->stat_lock);
+			sctx->stat.corrected_errors++;
+			sblock_to_check->data_corrected = 1;
+			spin_unlock(&sctx->stat_lock);
+			btrfs_err_rl_in_rcu(fs_info,
+				"fixed up error at logical %llu on dev %s",
+				logical, rcu_str_deref(dev->name));
+		}
+	} else {
+did_not_correct_error:
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.uncorrectable_errors++;
+		spin_unlock(&sctx->stat_lock);
+		btrfs_err_rl_in_rcu(fs_info,
+			"unable to fixup (regular) error at logical %llu on dev %s",
+			logical, rcu_str_deref(dev->name));
+	}
+
+out:
+	for (mirror_index = 0; mirror_index < BTRFS_MAX_MIRRORS; mirror_index++) {
+		struct scrub_block *sblock = sblocks_for_recheck[mirror_index];
+		struct scrub_recover *recover;
+		int sector_index;
+
+		/* Not allocated, continue checking the next mirror */
+		if (!sblock)
+			continue;
+
+		for (sector_index = 0; sector_index < sblock->sector_count;
+		     sector_index++) {
+			/*
+			 * Here we just cleanup the recover, each sector will be
+			 * properly cleaned up by later scrub_block_put()
+			 */
+			recover = sblock->sectors[sector_index]->recover;
+			if (recover) {
+				scrub_put_recover(fs_info, recover);
+				sblock->sectors[sector_index]->recover = NULL;
+			}
+		}
+		scrub_block_put(sblock);
+	}
+
+	ret = unlock_full_stripe(fs_info, logical, full_stripe_locked);
+	memalloc_nofs_restore(nofs_flag);
+	if (ret < 0)
+		return ret;
+	return 0;
+}
+
+static inline int scrub_nr_raid_mirrors(struct btrfs_io_context *bioc)
+{
+	if (bioc->map_type & BTRFS_BLOCK_GROUP_RAID5)
+		return 2;
+	else if (bioc->map_type & BTRFS_BLOCK_GROUP_RAID6)
+		return 3;
+	else
+		return (int)bioc->num_stripes;
+}
+
+static inline void scrub_stripe_index_and_offset(u64 logical, u64 map_type,
+						 u64 *raid_map,
+						 int nstripes, int mirror,
+						 int *stripe_index,
+						 u64 *stripe_offset)
+{
+	int i;
+
+	if (map_type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
+		/* RAID5/6 */
+		for (i = 0; i < nstripes; i++) {
+			if (raid_map[i] == RAID6_Q_STRIPE ||
+			    raid_map[i] == RAID5_P_STRIPE)
+				continue;
+
+			if (logical >= raid_map[i] &&
+			    logical < raid_map[i] + BTRFS_STRIPE_LEN)
+				break;
+		}
+
+		*stripe_index = i;
+		*stripe_offset = logical - raid_map[i];
+	} else {
+		/* The other RAID type */
+		*stripe_index = mirror;
+		*stripe_offset = 0;
+	}
+}
+
+static int scrub_setup_recheck_block(struct scrub_block *original_sblock,
+				     struct scrub_block *sblocks_for_recheck[])
+{
+	struct scrub_ctx *sctx = original_sblock->sctx;
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	u64 logical = original_sblock->logical;
+	u64 length = original_sblock->sector_count << fs_info->sectorsize_bits;
+	u64 generation = original_sblock->sectors[0]->generation;
+	u64 flags = original_sblock->sectors[0]->flags;
+	u64 have_csum = original_sblock->sectors[0]->have_csum;
+	struct scrub_recover *recover;
+	struct btrfs_io_context *bioc;
+	u64 sublen;
+	u64 mapped_length;
+	u64 stripe_offset;
+	int stripe_index;
+	int sector_index = 0;
+	int mirror_index;
+	int nmirrors;
+	int ret;
+
+	while (length > 0) {
+		sublen = min_t(u64, length, fs_info->sectorsize);
+		mapped_length = sublen;
+		bioc = NULL;
+
+		/*
+		 * With a length of sectorsize, each returned stripe represents
+		 * one mirror
+		 */
+		btrfs_bio_counter_inc_blocked(fs_info);
+		ret = btrfs_map_sblock(fs_info, BTRFS_MAP_GET_READ_MIRRORS,
+				       logical, &mapped_length, &bioc);
+		if (ret || !bioc || mapped_length < sublen) {
+			btrfs_put_bioc(bioc);
+			btrfs_bio_counter_dec(fs_info);
+			return -EIO;
+		}
+
+		recover = kzalloc(sizeof(struct scrub_recover), GFP_NOFS);
+		if (!recover) {
+			btrfs_put_bioc(bioc);
+			btrfs_bio_counter_dec(fs_info);
+			return -ENOMEM;
+		}
+
+		refcount_set(&recover->refs, 1);
+		recover->bioc = bioc;
+		recover->map_length = mapped_length;
+
+		ASSERT(sector_index < SCRUB_MAX_SECTORS_PER_BLOCK);
+
+		nmirrors = min(scrub_nr_raid_mirrors(bioc), BTRFS_MAX_MIRRORS);
+
+		for (mirror_index = 0; mirror_index < nmirrors;
+		     mirror_index++) {
+			struct scrub_block *sblock;
+			struct scrub_sector *sector;
+
+			sblock = sblocks_for_recheck[mirror_index];
+			sblock->sctx = sctx;
+
+			sector = alloc_scrub_sector(sblock, logical, GFP_NOFS);
+			if (!sector) {
+				spin_lock(&sctx->stat_lock);
+				sctx->stat.malloc_errors++;
+				spin_unlock(&sctx->stat_lock);
+				scrub_put_recover(fs_info, recover);
+				return -ENOMEM;
+			}
+			sector->flags = flags;
+			sector->generation = generation;
+			sector->have_csum = have_csum;
+			if (have_csum)
+				memcpy(sector->csum,
+				       original_sblock->sectors[0]->csum,
+				       sctx->fs_info->csum_size);
+
+			scrub_stripe_index_and_offset(logical,
+						      bioc->map_type,
+						      bioc->raid_map,
+						      bioc->num_stripes -
+						      bioc->num_tgtdevs,
+						      mirror_index,
+						      &stripe_index,
+						      &stripe_offset);
+			/*
+			 * We're at the first sector, also populate @sblock
+			 * physical and dev.
+			 */
+			if (sector_index == 0) {
+				sblock->physical =
+					bioc->stripes[stripe_index].physical +
+					stripe_offset;
+				sblock->dev = bioc->stripes[stripe_index].dev;
+				sblock->physical_for_dev_replace =
+					original_sblock->physical_for_dev_replace;
+			}
+
+			BUG_ON(sector_index >= original_sblock->sector_count);
+			scrub_get_recover(recover);
+			sector->recover = recover;
+		}
+		scrub_put_recover(fs_info, recover);
+		length -= sublen;
+		logical += sublen;
+		sector_index++;
+	}
+
+	return 0;
+}
+
+static void scrub_bio_wait_endio(struct bio *bio)
+{
+	complete(bio->bi_private);
+}
+
+static int scrub_submit_raid56_bio_wait(struct btrfs_fs_info *fs_info,
+					struct bio *bio,
+					struct scrub_sector *sector)
+{
+	DECLARE_COMPLETION_ONSTACK(done);
+
+	bio->bi_iter.bi_sector = (sector->offset + sector->sblock->logical) >>
+				 SECTOR_SHIFT;
+	bio->bi_private = &done;
+	bio->bi_end_io = scrub_bio_wait_endio;
+	raid56_parity_recover(bio, sector->recover->bioc, sector->sblock->mirror_num);
+
+	wait_for_completion_io(&done);
+	return blk_status_to_errno(bio->bi_status);
+}
+
+static void scrub_recheck_block_on_raid56(struct btrfs_fs_info *fs_info,
+					  struct scrub_block *sblock)
+{
+	struct scrub_sector *first_sector = sblock->sectors[0];
+	struct bio *bio;
+	int i;
+
+	/* All sectors in sblock belong to the same stripe on the same device. */
+	ASSERT(sblock->dev);
+	if (!sblock->dev->bdev)
+		goto out;
+
+	bio = bio_alloc(sblock->dev->bdev, BIO_MAX_VECS, REQ_OP_READ, GFP_NOFS);
+
+	for (i = 0; i < sblock->sector_count; i++) {
+		struct scrub_sector *sector = sblock->sectors[i];
+
+		bio_add_scrub_sector(bio, sector, fs_info->sectorsize);
+	}
+
+	if (scrub_submit_raid56_bio_wait(fs_info, bio, first_sector)) {
+		bio_put(bio);
+		goto out;
+	}
+
+	bio_put(bio);
+
+	scrub_recheck_block_checksum(sblock);
+
+	return;
+out:
+	for (i = 0; i < sblock->sector_count; i++)
+		sblock->sectors[i]->io_error = 1;
+
+	sblock->no_io_error_seen = 0;
+}
+
+/*
+ * This function will check the on disk data for checksum errors, header errors
+ * and read I/O errors. If any I/O errors happen, the exact sectors which are
+ * errored are marked as being bad. The goal is to enable scrub to take those
+ * sectors that are not errored from all the mirrors so that the sectors that
+ * are errored in the just handled mirror can be repaired.
+ */
+static void scrub_recheck_block(struct btrfs_fs_info *fs_info,
+				struct scrub_block *sblock,
+				int retry_failed_mirror)
+{
+	int i;
+
+	sblock->no_io_error_seen = 1;
+
+	/* short cut for raid56 */
+	if (!retry_failed_mirror && scrub_is_page_on_raid56(sblock->sectors[0]))
+		return scrub_recheck_block_on_raid56(fs_info, sblock);
+
+	for (i = 0; i < sblock->sector_count; i++) {
+		struct scrub_sector *sector = sblock->sectors[i];
+		struct bio bio;
+		struct bio_vec bvec;
+
+		if (sblock->dev->bdev == NULL) {
+			sector->io_error = 1;
+			sblock->no_io_error_seen = 0;
+			continue;
+		}
+
+		bio_init(&bio, sblock->dev->bdev, &bvec, 1, REQ_OP_READ);
+		bio_add_scrub_sector(&bio, sector, fs_info->sectorsize);
+		bio.bi_iter.bi_sector = (sblock->physical + sector->offset) >>
+					SECTOR_SHIFT;
+
+		btrfsic_check_bio(&bio);
+		if (submit_bio_wait(&bio)) {
+			sector->io_error = 1;
+			sblock->no_io_error_seen = 0;
+		}
+
+		bio_uninit(&bio);
+	}
+
+	if (sblock->no_io_error_seen)
+		scrub_recheck_block_checksum(sblock);
+}
+
+static inline int scrub_check_fsid(u8 fsid[], struct scrub_sector *sector)
+{
+	struct btrfs_fs_devices *fs_devices = sector->sblock->dev->fs_devices;
+	int ret;
+
+	ret = memcmp(fsid, fs_devices->fsid, BTRFS_FSID_SIZE);
+	return !ret;
+}
+
+static void scrub_recheck_block_checksum(struct scrub_block *sblock)
+{
+	sblock->header_error = 0;
+	sblock->checksum_error = 0;
+	sblock->generation_error = 0;
+
+	if (sblock->sectors[0]->flags & BTRFS_EXTENT_FLAG_DATA)
+		scrub_checksum_data(sblock);
+	else
+		scrub_checksum_tree_block(sblock);
+}
+
+static int scrub_repair_block_from_good_copy(struct scrub_block *sblock_bad,
+					     struct scrub_block *sblock_good)
+{
+	int i;
+	int ret = 0;
+
+	for (i = 0; i < sblock_bad->sector_count; i++) {
+		int ret_sub;
+
+		ret_sub = scrub_repair_sector_from_good_copy(sblock_bad,
+							     sblock_good, i, 1);
+		if (ret_sub)
+			ret = ret_sub;
+	}
+
+	return ret;
+}
+
+static int scrub_repair_sector_from_good_copy(struct scrub_block *sblock_bad,
+					      struct scrub_block *sblock_good,
+					      int sector_num, int force_write)
+{
+	struct scrub_sector *sector_bad = sblock_bad->sectors[sector_num];
+	struct scrub_sector *sector_good = sblock_good->sectors[sector_num];
+	struct btrfs_fs_info *fs_info = sblock_bad->sctx->fs_info;
+	const u32 sectorsize = fs_info->sectorsize;
+
+	if (force_write || sblock_bad->header_error ||
+	    sblock_bad->checksum_error || sector_bad->io_error) {
+		struct bio bio;
+		struct bio_vec bvec;
+		int ret;
+
+		if (!sblock_bad->dev->bdev) {
+			btrfs_warn_rl(fs_info,
+				"scrub_repair_page_from_good_copy(bdev == NULL) is unexpected");
+			return -EIO;
+		}
+
+		bio_init(&bio, sblock_bad->dev->bdev, &bvec, 1, REQ_OP_WRITE);
+		bio.bi_iter.bi_sector = (sblock_bad->physical +
+					 sector_bad->offset) >> SECTOR_SHIFT;
+		ret = bio_add_scrub_sector(&bio, sector_good, sectorsize);
+
+		btrfsic_check_bio(&bio);
+		ret = submit_bio_wait(&bio);
+		bio_uninit(&bio);
+
+		if (ret) {
+			btrfs_dev_stat_inc_and_print(sblock_bad->dev,
+				BTRFS_DEV_STAT_WRITE_ERRS);
+			atomic64_inc(&fs_info->dev_replace.num_write_errors);
+			return -EIO;
+		}
+	}
+
+	return 0;
+}
+
+static void scrub_write_block_to_dev_replace(struct scrub_block *sblock)
+{
+	struct btrfs_fs_info *fs_info = sblock->sctx->fs_info;
+	int i;
+
+	/*
+	 * This block is used for the check of the parity on the source device,
+	 * so the data needn't be written into the destination device.
+	 */
+	if (sblock->sparity)
+		return;
+
+	for (i = 0; i < sblock->sector_count; i++) {
+		int ret;
+
+		ret = scrub_write_sector_to_dev_replace(sblock, i);
+		if (ret)
+			atomic64_inc(&fs_info->dev_replace.num_write_errors);
+	}
+}
+
+static int scrub_write_sector_to_dev_replace(struct scrub_block *sblock, int sector_num)
+{
+	const u32 sectorsize = sblock->sctx->fs_info->sectorsize;
+	struct scrub_sector *sector = sblock->sectors[sector_num];
+
+	if (sector->io_error)
+		memset(scrub_sector_get_kaddr(sector), 0, sectorsize);
+
+	return scrub_add_sector_to_wr_bio(sblock->sctx, sector);
+}
+
+static int fill_writer_pointer_gap(struct scrub_ctx *sctx, u64 physical)
+{
+	int ret = 0;
+	u64 length;
+
+	if (!btrfs_is_zoned(sctx->fs_info))
+		return 0;
+
+	if (!btrfs_dev_is_sequential(sctx->wr_tgtdev, physical))
+		return 0;
+
+	if (sctx->write_pointer < physical) {
+		length = physical - sctx->write_pointer;
+
+		ret = btrfs_zoned_issue_zeroout(sctx->wr_tgtdev,
+						sctx->write_pointer, length);
+		if (!ret)
+			sctx->write_pointer = physical;
+	}
+	return ret;
+}
+
+static void scrub_block_get(struct scrub_block *sblock)
+{
+	refcount_inc(&sblock->refs);
+}
+
+static int scrub_add_sector_to_wr_bio(struct scrub_ctx *sctx,
+				      struct scrub_sector *sector)
+{
+	struct scrub_block *sblock = sector->sblock;
+	struct scrub_bio *sbio;
+	int ret;
+	const u32 sectorsize = sctx->fs_info->sectorsize;
+
+	mutex_lock(&sctx->wr_lock);
+again:
+	if (!sctx->wr_curr_bio) {
+		sctx->wr_curr_bio = kzalloc(sizeof(*sctx->wr_curr_bio),
+					      GFP_KERNEL);
+		if (!sctx->wr_curr_bio) {
+			mutex_unlock(&sctx->wr_lock);
+			return -ENOMEM;
+		}
+		sctx->wr_curr_bio->sctx = sctx;
+		sctx->wr_curr_bio->sector_count = 0;
+	}
+	sbio = sctx->wr_curr_bio;
+	if (sbio->sector_count == 0) {
+		ret = fill_writer_pointer_gap(sctx, sector->offset +
+					      sblock->physical_for_dev_replace);
+		if (ret) {
+			mutex_unlock(&sctx->wr_lock);
+			return ret;
+		}
+
+		sbio->physical = sblock->physical_for_dev_replace + sector->offset;
+		sbio->logical = sblock->logical + sector->offset;
+		sbio->dev = sctx->wr_tgtdev;
+		if (!sbio->bio) {
+			sbio->bio = bio_alloc(sbio->dev->bdev, sctx->sectors_per_bio,
+					      REQ_OP_WRITE, GFP_NOFS);
+		}
+		sbio->bio->bi_private = sbio;
+		sbio->bio->bi_end_io = scrub_wr_bio_end_io;
+		sbio->bio->bi_iter.bi_sector = sbio->physical >> 9;
+		sbio->status = 0;
+	} else if (sbio->physical + sbio->sector_count * sectorsize !=
+		   sblock->physical_for_dev_replace + sector->offset ||
+		   sbio->logical + sbio->sector_count * sectorsize !=
+		   sblock->logical + sector->offset) {
+		scrub_wr_submit(sctx);
+		goto again;
+	}
+
+	ret = bio_add_scrub_sector(sbio->bio, sector, sectorsize);
+	if (ret != sectorsize) {
+		if (sbio->sector_count < 1) {
+			bio_put(sbio->bio);
+			sbio->bio = NULL;
+			mutex_unlock(&sctx->wr_lock);
+			return -EIO;
+		}
+		scrub_wr_submit(sctx);
+		goto again;
+	}
+
+	sbio->sectors[sbio->sector_count] = sector;
+	scrub_sector_get(sector);
+	/*
+	 * Since ssector no longer holds a page, but uses sblock::pages, we
+	 * have to ensure the sblock had not been freed before our write bio
+	 * finished.
+	 */
+	scrub_block_get(sector->sblock);
+
+	sbio->sector_count++;
+	if (sbio->sector_count == sctx->sectors_per_bio)
+		scrub_wr_submit(sctx);
+	mutex_unlock(&sctx->wr_lock);
+
+	return 0;
+}
+
+static void scrub_wr_submit(struct scrub_ctx *sctx)
+{
+	struct scrub_bio *sbio;
+
+	if (!sctx->wr_curr_bio)
+		return;
+
+	sbio = sctx->wr_curr_bio;
+	sctx->wr_curr_bio = NULL;
+	scrub_pending_bio_inc(sctx);
+	/* process all writes in a single worker thread. Then the block layer
+	 * orders the requests before sending them to the driver which
+	 * doubled the write performance on spinning disks when measured
+	 * with Linux 3.5 */
+	btrfsic_check_bio(sbio->bio);
+	submit_bio(sbio->bio);
+
+	if (btrfs_is_zoned(sctx->fs_info))
+		sctx->write_pointer = sbio->physical + sbio->sector_count *
+			sctx->fs_info->sectorsize;
+}
+
+static void scrub_wr_bio_end_io(struct bio *bio)
+{
+	struct scrub_bio *sbio = bio->bi_private;
+	struct btrfs_fs_info *fs_info = sbio->dev->fs_info;
+
+	sbio->status = bio->bi_status;
+	sbio->bio = bio;
+
+	INIT_WORK(&sbio->work, scrub_wr_bio_end_io_worker);
+	queue_work(fs_info->scrub_wr_completion_workers, &sbio->work);
+}
+
+static void scrub_wr_bio_end_io_worker(struct work_struct *work)
+{
+	struct scrub_bio *sbio = container_of(work, struct scrub_bio, work);
+	struct scrub_ctx *sctx = sbio->sctx;
+	int i;
+
+	ASSERT(sbio->sector_count <= SCRUB_SECTORS_PER_BIO);
+	if (sbio->status) {
+		struct btrfs_dev_replace *dev_replace =
+			&sbio->sctx->fs_info->dev_replace;
+
+		for (i = 0; i < sbio->sector_count; i++) {
+			struct scrub_sector *sector = sbio->sectors[i];
+
+			sector->io_error = 1;
+			atomic64_inc(&dev_replace->num_write_errors);
+		}
+	}
+
+	/*
+	 * In scrub_add_sector_to_wr_bio() we grab extra ref for sblock, now in
+	 * endio we should put the sblock.
+	 */
+	for (i = 0; i < sbio->sector_count; i++) {
+		scrub_block_put(sbio->sectors[i]->sblock);
+		scrub_sector_put(sbio->sectors[i]);
+	}
+
+	bio_put(sbio->bio);
+	kfree(sbio);
+	scrub_pending_bio_dec(sctx);
+}
+
+static int scrub_checksum(struct scrub_block *sblock)
+{
+	u64 flags;
+	int ret;
+
+	/*
+	 * No need to initialize these stats currently,
+	 * because this function only use return value
+	 * instead of these stats value.
+	 *
+	 * Todo:
+	 * always use stats
+	 */
+	sblock->header_error = 0;
+	sblock->generation_error = 0;
+	sblock->checksum_error = 0;
+
+	WARN_ON(sblock->sector_count < 1);
+	flags = sblock->sectors[0]->flags;
+	ret = 0;
+	if (flags & BTRFS_EXTENT_FLAG_DATA)
+		ret = scrub_checksum_data(sblock);
+	else if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)
+		ret = scrub_checksum_tree_block(sblock);
+	else if (flags & BTRFS_EXTENT_FLAG_SUPER)
+		ret = scrub_checksum_super(sblock);
+	else
+		WARN_ON(1);
+	if (ret)
+		scrub_handle_errored_block(sblock);
+
+	return ret;
+}
+
+static int scrub_checksum_data(struct scrub_block *sblock)
+{
+	struct scrub_ctx *sctx = sblock->sctx;
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
+	u8 csum[BTRFS_CSUM_SIZE];
+	struct scrub_sector *sector;
+	char *kaddr;
+
+	BUG_ON(sblock->sector_count < 1);
+	sector = sblock->sectors[0];
+	if (!sector->have_csum)
+		return 0;
+
+	kaddr = scrub_sector_get_kaddr(sector);
+
+	shash->tfm = fs_info->csum_shash;
+	crypto_shash_init(shash);
+
+	crypto_shash_digest(shash, kaddr, fs_info->sectorsize, csum);
+
+	if (memcmp(csum, sector->csum, fs_info->csum_size))
+		sblock->checksum_error = 1;
+	return sblock->checksum_error;
+}
+
+static int scrub_checksum_tree_block(struct scrub_block *sblock)
+{
+	struct scrub_ctx *sctx = sblock->sctx;
+	struct btrfs_header *h;
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
+	u8 calculated_csum[BTRFS_CSUM_SIZE];
+	u8 on_disk_csum[BTRFS_CSUM_SIZE];
+	/*
+	 * This is done in sectorsize steps even for metadata as there's a
+	 * constraint for nodesize to be aligned to sectorsize. This will need
+	 * to change so we don't misuse data and metadata units like that.
+	 */
+	const u32 sectorsize = sctx->fs_info->sectorsize;
+	const int num_sectors = fs_info->nodesize >> fs_info->sectorsize_bits;
+	int i;
+	struct scrub_sector *sector;
+	char *kaddr;
+
+	BUG_ON(sblock->sector_count < 1);
+
+	/* Each member in sectors is just one sector */
+	ASSERT(sblock->sector_count == num_sectors);
+
+	sector = sblock->sectors[0];
+	kaddr = scrub_sector_get_kaddr(sector);
+	h = (struct btrfs_header *)kaddr;
+	memcpy(on_disk_csum, h->csum, sctx->fs_info->csum_size);
+
+	/*
+	 * we don't use the getter functions here, as we
+	 * a) don't have an extent buffer and
+	 * b) the page is already kmapped
+	 */
+	if (sblock->logical != btrfs_stack_header_bytenr(h)) {
+		sblock->header_error = 1;
+		btrfs_warn_rl(fs_info,
+		"tree block %llu mirror %u has bad bytenr, has %llu want %llu",
+			      sblock->logical, sblock->mirror_num,
+			      btrfs_stack_header_bytenr(h),
+			      sblock->logical);
+		goto out;
+	}
+
+	if (!scrub_check_fsid(h->fsid, sector)) {
+		sblock->header_error = 1;
+		btrfs_warn_rl(fs_info,
+		"tree block %llu mirror %u has bad fsid, has %pU want %pU",
+			      sblock->logical, sblock->mirror_num,
+			      h->fsid, sblock->dev->fs_devices->fsid);
+		goto out;
+	}
+
+	if (memcmp(h->chunk_tree_uuid, fs_info->chunk_tree_uuid, BTRFS_UUID_SIZE)) {
+		sblock->header_error = 1;
+		btrfs_warn_rl(fs_info,
+		"tree block %llu mirror %u has bad chunk tree uuid, has %pU want %pU",
+			      sblock->logical, sblock->mirror_num,
+			      h->chunk_tree_uuid, fs_info->chunk_tree_uuid);
+		goto out;
+	}
+
+	shash->tfm = fs_info->csum_shash;
+	crypto_shash_init(shash);
+	crypto_shash_update(shash, kaddr + BTRFS_CSUM_SIZE,
+			    sectorsize - BTRFS_CSUM_SIZE);
+
+	for (i = 1; i < num_sectors; i++) {
+		kaddr = scrub_sector_get_kaddr(sblock->sectors[i]);
+		crypto_shash_update(shash, kaddr, sectorsize);
+	}
+
+	crypto_shash_final(shash, calculated_csum);
+	if (memcmp(calculated_csum, on_disk_csum, sctx->fs_info->csum_size)) {
+		sblock->checksum_error = 1;
+		btrfs_warn_rl(fs_info,
+		"tree block %llu mirror %u has bad csum, has " CSUM_FMT " want " CSUM_FMT,
+			      sblock->logical, sblock->mirror_num,
+			      CSUM_FMT_VALUE(fs_info->csum_size, on_disk_csum),
+			      CSUM_FMT_VALUE(fs_info->csum_size, calculated_csum));
+		goto out;
+	}
+
+	if (sector->generation != btrfs_stack_header_generation(h)) {
+		sblock->header_error = 1;
+		sblock->generation_error = 1;
+		btrfs_warn_rl(fs_info,
+		"tree block %llu mirror %u has bad generation, has %llu want %llu",
+			      sblock->logical, sblock->mirror_num,
+			      btrfs_stack_header_generation(h),
+			      sector->generation);
+	}
+
+out:
+	return sblock->header_error || sblock->checksum_error;
+}
+
+static int scrub_checksum_super(struct scrub_block *sblock)
+{
+	struct btrfs_super_block *s;
+	struct scrub_ctx *sctx = sblock->sctx;
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
+	u8 calculated_csum[BTRFS_CSUM_SIZE];
+	struct scrub_sector *sector;
+	char *kaddr;
+	int fail_gen = 0;
+	int fail_cor = 0;
+
+	BUG_ON(sblock->sector_count < 1);
+	sector = sblock->sectors[0];
+	kaddr = scrub_sector_get_kaddr(sector);
+	s = (struct btrfs_super_block *)kaddr;
+
+	if (sblock->logical != btrfs_super_bytenr(s))
+		++fail_cor;
+
+	if (sector->generation != btrfs_super_generation(s))
+		++fail_gen;
+
+	if (!scrub_check_fsid(s->fsid, sector))
+		++fail_cor;
+
+	shash->tfm = fs_info->csum_shash;
+	crypto_shash_init(shash);
+	crypto_shash_digest(shash, kaddr + BTRFS_CSUM_SIZE,
+			BTRFS_SUPER_INFO_SIZE - BTRFS_CSUM_SIZE, calculated_csum);
+
+	if (memcmp(calculated_csum, s->csum, sctx->fs_info->csum_size))
+		++fail_cor;
+
+	return fail_cor + fail_gen;
+}
+
+static void scrub_block_put(struct scrub_block *sblock)
+{
+	if (refcount_dec_and_test(&sblock->refs)) {
+		int i;
+
+		if (sblock->sparity)
+			scrub_parity_put(sblock->sparity);
+
+		for (i = 0; i < sblock->sector_count; i++)
+			scrub_sector_put(sblock->sectors[i]);
+		for (i = 0; i < DIV_ROUND_UP(sblock->len, PAGE_SIZE); i++) {
+			if (sblock->pages[i]) {
+				detach_scrub_page_private(sblock->pages[i]);
+				__free_page(sblock->pages[i]);
+			}
+		}
+		kfree(sblock);
+	}
+}
+
+static void scrub_sector_get(struct scrub_sector *sector)
+{
+	atomic_inc(&sector->refs);
+}
+
+static void scrub_sector_put(struct scrub_sector *sector)
+{
+	if (atomic_dec_and_test(&sector->refs))
+		kfree(sector);
+}
+
+/*
+ * Throttling of IO submission, bandwidth-limit based, the timeslice is 1
+ * second.  Limit can be set via /sys/fs/UUID/devinfo/devid/scrub_speed_max.
+ */
+static void scrub_throttle(struct scrub_ctx *sctx)
+{
+	const int time_slice = 1000;
+	struct scrub_bio *sbio;
+	struct btrfs_device *device;
+	s64 delta;
+	ktime_t now;
+	u32 div;
+	u64 bwlimit;
+
+	sbio = sctx->bios[sctx->curr];
+	device = sbio->dev;
+	bwlimit = READ_ONCE(device->scrub_speed_max);
+	if (bwlimit == 0)
+		return;
+
+	/*
+	 * Slice is divided into intervals when the IO is submitted, adjust by
+	 * bwlimit and maximum of 64 intervals.
+	 */
+	div = max_t(u32, 1, (u32)(bwlimit / (16 * 1024 * 1024)));
+	div = min_t(u32, 64, div);
+
+	/* Start new epoch, set deadline */
+	now = ktime_get();
+	if (sctx->throttle_deadline == 0) {
+		sctx->throttle_deadline = ktime_add_ms(now, time_slice / div);
+		sctx->throttle_sent = 0;
+	}
+
+	/* Still in the time to send? */
+	if (ktime_before(now, sctx->throttle_deadline)) {
+		/* If current bio is within the limit, send it */
+		sctx->throttle_sent += sbio->bio->bi_iter.bi_size;
+		if (sctx->throttle_sent <= div_u64(bwlimit, div))
+			return;
+
+		/* We're over the limit, sleep until the rest of the slice */
+		delta = ktime_ms_delta(sctx->throttle_deadline, now);
+	} else {
+		/* New request after deadline, start new epoch */
+		delta = 0;
+	}
+
+	if (delta) {
+		long timeout;
+
+		timeout = div_u64(delta * HZ, 1000);
+		schedule_timeout_interruptible(timeout);
+	}
+
+	/* Next call will start the deadline period */
+	sctx->throttle_deadline = 0;
+}
+
+static void scrub_submit(struct scrub_ctx *sctx)
+{
+	struct scrub_bio *sbio;
+
+	if (sctx->curr == -1)
+		return;
+
+	scrub_throttle(sctx);
+
+	sbio = sctx->bios[sctx->curr];
+	sctx->curr = -1;
+	scrub_pending_bio_inc(sctx);
+	btrfsic_check_bio(sbio->bio);
+	submit_bio(sbio->bio);
+}
+
+static int scrub_add_sector_to_rd_bio(struct scrub_ctx *sctx,
+				      struct scrub_sector *sector)
+{
+	struct scrub_block *sblock = sector->sblock;
+	struct scrub_bio *sbio;
+	const u32 sectorsize = sctx->fs_info->sectorsize;
+	int ret;
+
+again:
+	/*
+	 * grab a fresh bio or wait for one to become available
+	 */
+	while (sctx->curr == -1) {
+		spin_lock(&sctx->list_lock);
+		sctx->curr = sctx->first_free;
+		if (sctx->curr != -1) {
+			sctx->first_free = sctx->bios[sctx->curr]->next_free;
+			sctx->bios[sctx->curr]->next_free = -1;
+			sctx->bios[sctx->curr]->sector_count = 0;
+			spin_unlock(&sctx->list_lock);
+		} else {
+			spin_unlock(&sctx->list_lock);
+			wait_event(sctx->list_wait, sctx->first_free != -1);
+		}
+	}
+	sbio = sctx->bios[sctx->curr];
+	if (sbio->sector_count == 0) {
+		sbio->physical = sblock->physical + sector->offset;
+		sbio->logical = sblock->logical + sector->offset;
+		sbio->dev = sblock->dev;
+		if (!sbio->bio) {
+			sbio->bio = bio_alloc(sbio->dev->bdev, sctx->sectors_per_bio,
+					      REQ_OP_READ, GFP_NOFS);
+		}
+		sbio->bio->bi_private = sbio;
+		sbio->bio->bi_end_io = scrub_bio_end_io;
+		sbio->bio->bi_iter.bi_sector = sbio->physical >> 9;
+		sbio->status = 0;
+	} else if (sbio->physical + sbio->sector_count * sectorsize !=
+		   sblock->physical + sector->offset ||
+		   sbio->logical + sbio->sector_count * sectorsize !=
+		   sblock->logical + sector->offset ||
+		   sbio->dev != sblock->dev) {
+		scrub_submit(sctx);
+		goto again;
+	}
+
+	sbio->sectors[sbio->sector_count] = sector;
+	ret = bio_add_scrub_sector(sbio->bio, sector, sectorsize);
+	if (ret != sectorsize) {
+		if (sbio->sector_count < 1) {
+			bio_put(sbio->bio);
+			sbio->bio = NULL;
+			return -EIO;
+		}
+		scrub_submit(sctx);
+		goto again;
+	}
+
+	scrub_block_get(sblock); /* one for the page added to the bio */
+	atomic_inc(&sblock->outstanding_sectors);
+	sbio->sector_count++;
+	if (sbio->sector_count == sctx->sectors_per_bio)
+		scrub_submit(sctx);
+
+	return 0;
+}
+
+static void scrub_missing_raid56_end_io(struct bio *bio)
+{
+	struct scrub_block *sblock = bio->bi_private;
+	struct btrfs_fs_info *fs_info = sblock->sctx->fs_info;
+
+	btrfs_bio_counter_dec(fs_info);
+	if (bio->bi_status)
+		sblock->no_io_error_seen = 0;
+
+	bio_put(bio);
+
+	queue_work(fs_info->scrub_workers, &sblock->work);
+}
+
+static void scrub_missing_raid56_worker(struct work_struct *work)
+{
+	struct scrub_block *sblock = container_of(work, struct scrub_block, work);
+	struct scrub_ctx *sctx = sblock->sctx;
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	u64 logical;
+	struct btrfs_device *dev;
+
+	logical = sblock->logical;
+	dev = sblock->dev;
+
+	if (sblock->no_io_error_seen)
+		scrub_recheck_block_checksum(sblock);
+
+	if (!sblock->no_io_error_seen) {
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.read_errors++;
+		spin_unlock(&sctx->stat_lock);
+		btrfs_err_rl_in_rcu(fs_info,
+			"IO error rebuilding logical %llu for dev %s",
+			logical, rcu_str_deref(dev->name));
+	} else if (sblock->header_error || sblock->checksum_error) {
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.uncorrectable_errors++;
+		spin_unlock(&sctx->stat_lock);
+		btrfs_err_rl_in_rcu(fs_info,
+			"failed to rebuild valid logical %llu for dev %s",
+			logical, rcu_str_deref(dev->name));
+	} else {
+		scrub_write_block_to_dev_replace(sblock);
+	}
+
+	if (sctx->is_dev_replace && sctx->flush_all_writes) {
+		mutex_lock(&sctx->wr_lock);
+		scrub_wr_submit(sctx);
+		mutex_unlock(&sctx->wr_lock);
+	}
+
+	scrub_block_put(sblock);
+	scrub_pending_bio_dec(sctx);
+}
+
+static void scrub_missing_raid56_pages(struct scrub_block *sblock)
+{
+	struct scrub_ctx *sctx = sblock->sctx;
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	u64 length = sblock->sector_count << fs_info->sectorsize_bits;
+	u64 logical = sblock->logical;
+	struct btrfs_io_context *bioc = NULL;
+	struct bio *bio;
+	struct btrfs_raid_bio *rbio;
+	int ret;
+	int i;
+
+	btrfs_bio_counter_inc_blocked(fs_info);
+	ret = btrfs_map_sblock(fs_info, BTRFS_MAP_GET_READ_MIRRORS, logical,
+			       &length, &bioc);
+	if (ret || !bioc || !bioc->raid_map)
+		goto bioc_out;
+
+	if (WARN_ON(!sctx->is_dev_replace ||
+		    !(bioc->map_type & BTRFS_BLOCK_GROUP_RAID56_MASK))) {
+		/*
+		 * We shouldn't be scrubbing a missing device. Even for dev
+		 * replace, we should only get here for RAID 5/6. We either
+		 * managed to mount something with no mirrors remaining or
+		 * there's a bug in scrub_find_good_copy()/btrfs_map_block().
+		 */
+		goto bioc_out;
+	}
+
+	bio = bio_alloc(NULL, BIO_MAX_VECS, REQ_OP_READ, GFP_NOFS);
+	bio->bi_iter.bi_sector = logical >> 9;
+	bio->bi_private = sblock;
+	bio->bi_end_io = scrub_missing_raid56_end_io;
+
+	rbio = raid56_alloc_missing_rbio(bio, bioc);
+	if (!rbio)
+		goto rbio_out;
+
+	for (i = 0; i < sblock->sector_count; i++) {
+		struct scrub_sector *sector = sblock->sectors[i];
+
+		raid56_add_scrub_pages(rbio, scrub_sector_get_page(sector),
+				       scrub_sector_get_page_offset(sector),
+				       sector->offset + sector->sblock->logical);
+	}
+
+	INIT_WORK(&sblock->work, scrub_missing_raid56_worker);
+	scrub_block_get(sblock);
+	scrub_pending_bio_inc(sctx);
+	raid56_submit_missing_rbio(rbio);
+	btrfs_put_bioc(bioc);
+	return;
+
+rbio_out:
+	bio_put(bio);
+bioc_out:
+	btrfs_bio_counter_dec(fs_info);
+	btrfs_put_bioc(bioc);
+	spin_lock(&sctx->stat_lock);
+	sctx->stat.malloc_errors++;
+	spin_unlock(&sctx->stat_lock);
+}
+
+static int scrub_sectors(struct scrub_ctx *sctx, u64 logical, u32 len,
+		       u64 physical, struct btrfs_device *dev, u64 flags,
+		       u64 gen, int mirror_num, u8 *csum,
+		       u64 physical_for_dev_replace)
+{
+	struct scrub_block *sblock;
+	const u32 sectorsize = sctx->fs_info->sectorsize;
+	int index;
+
+	sblock = alloc_scrub_block(sctx, dev, logical, physical,
+				   physical_for_dev_replace, mirror_num);
+	if (!sblock) {
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.malloc_errors++;
+		spin_unlock(&sctx->stat_lock);
+		return -ENOMEM;
+	}
+
+	for (index = 0; len > 0; index++) {
+		struct scrub_sector *sector;
+		/*
+		 * Here we will allocate one page for one sector to scrub.
+		 * This is fine if PAGE_SIZE == sectorsize, but will cost
+		 * more memory for PAGE_SIZE > sectorsize case.
+		 */
+		u32 l = min(sectorsize, len);
+
+		sector = alloc_scrub_sector(sblock, logical, GFP_KERNEL);
+		if (!sector) {
+			spin_lock(&sctx->stat_lock);
+			sctx->stat.malloc_errors++;
+			spin_unlock(&sctx->stat_lock);
+			scrub_block_put(sblock);
+			return -ENOMEM;
+		}
+		sector->flags = flags;
+		sector->generation = gen;
+		if (csum) {
+			sector->have_csum = 1;
+			memcpy(sector->csum, csum, sctx->fs_info->csum_size);
+		} else {
+			sector->have_csum = 0;
+		}
+		len -= l;
+		logical += l;
+		physical += l;
+		physical_for_dev_replace += l;
+	}
+
+	WARN_ON(sblock->sector_count == 0);
+	if (test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state)) {
+		/*
+		 * This case should only be hit for RAID 5/6 device replace. See
+		 * the comment in scrub_missing_raid56_pages() for details.
+		 */
+		scrub_missing_raid56_pages(sblock);
+	} else {
+		for (index = 0; index < sblock->sector_count; index++) {
+			struct scrub_sector *sector = sblock->sectors[index];
+			int ret;
+
+			ret = scrub_add_sector_to_rd_bio(sctx, sector);
+			if (ret) {
+				scrub_block_put(sblock);
+				return ret;
+			}
+		}
+
+		if (flags & BTRFS_EXTENT_FLAG_SUPER)
+			scrub_submit(sctx);
+	}
+
+	/* last one frees, either here or in bio completion for last page */
+	scrub_block_put(sblock);
+	return 0;
+}
+
+static void scrub_bio_end_io(struct bio *bio)
+{
+	struct scrub_bio *sbio = bio->bi_private;
+	struct btrfs_fs_info *fs_info = sbio->dev->fs_info;
+
+	sbio->status = bio->bi_status;
+	sbio->bio = bio;
+
+	queue_work(fs_info->scrub_workers, &sbio->work);
+}
+
+static void scrub_bio_end_io_worker(struct work_struct *work)
+{
+	struct scrub_bio *sbio = container_of(work, struct scrub_bio, work);
+	struct scrub_ctx *sctx = sbio->sctx;
+	int i;
+
+	ASSERT(sbio->sector_count <= SCRUB_SECTORS_PER_BIO);
+	if (sbio->status) {
+		for (i = 0; i < sbio->sector_count; i++) {
+			struct scrub_sector *sector = sbio->sectors[i];
+
+			sector->io_error = 1;
+			sector->sblock->no_io_error_seen = 0;
+		}
+	}
+
+	/* Now complete the scrub_block items that have all pages completed */
+	for (i = 0; i < sbio->sector_count; i++) {
+		struct scrub_sector *sector = sbio->sectors[i];
+		struct scrub_block *sblock = sector->sblock;
+
+		if (atomic_dec_and_test(&sblock->outstanding_sectors))
+			scrub_block_complete(sblock);
+		scrub_block_put(sblock);
+	}
+
+	bio_put(sbio->bio);
+	sbio->bio = NULL;
+	spin_lock(&sctx->list_lock);
+	sbio->next_free = sctx->first_free;
+	sctx->first_free = sbio->index;
+	spin_unlock(&sctx->list_lock);
+
+	if (sctx->is_dev_replace && sctx->flush_all_writes) {
+		mutex_lock(&sctx->wr_lock);
+		scrub_wr_submit(sctx);
+		mutex_unlock(&sctx->wr_lock);
+	}
+
+	scrub_pending_bio_dec(sctx);
+}
+
+static inline void __scrub_mark_bitmap(struct scrub_parity *sparity,
+				       unsigned long *bitmap,
+				       u64 start, u32 len)
+{
+	u64 offset;
+	u32 nsectors;
+	u32 sectorsize_bits = sparity->sctx->fs_info->sectorsize_bits;
+
+	if (len >= sparity->stripe_len) {
+		bitmap_set(bitmap, 0, sparity->nsectors);
+		return;
+	}
+
+	start -= sparity->logic_start;
+	start = div64_u64_rem(start, sparity->stripe_len, &offset);
+	offset = offset >> sectorsize_bits;
+	nsectors = len >> sectorsize_bits;
+
+	if (offset + nsectors <= sparity->nsectors) {
+		bitmap_set(bitmap, offset, nsectors);
+		return;
+	}
+
+	bitmap_set(bitmap, offset, sparity->nsectors - offset);
+	bitmap_set(bitmap, 0, nsectors - (sparity->nsectors - offset));
+}
+
+static inline void scrub_parity_mark_sectors_error(struct scrub_parity *sparity,
+						   u64 start, u32 len)
+{
+	__scrub_mark_bitmap(sparity, &sparity->ebitmap, start, len);
+}
+
+static inline void scrub_parity_mark_sectors_data(struct scrub_parity *sparity,
+						  u64 start, u32 len)
+{
+	__scrub_mark_bitmap(sparity, &sparity->dbitmap, start, len);
+}
+
+static void scrub_block_complete(struct scrub_block *sblock)
+{
+	int corrupted = 0;
+
+	if (!sblock->no_io_error_seen) {
+		corrupted = 1;
+		scrub_handle_errored_block(sblock);
+	} else {
+		/*
+		 * if has checksum error, write via repair mechanism in
+		 * dev replace case, otherwise write here in dev replace
+		 * case.
+		 */
+		corrupted = scrub_checksum(sblock);
+		if (!corrupted && sblock->sctx->is_dev_replace)
+			scrub_write_block_to_dev_replace(sblock);
+	}
+
+	if (sblock->sparity && corrupted && !sblock->data_corrected) {
+		u64 start = sblock->logical;
+		u64 end = sblock->logical +
+			  sblock->sectors[sblock->sector_count - 1]->offset +
+			  sblock->sctx->fs_info->sectorsize;
+
+		ASSERT(end - start <= U32_MAX);
+		scrub_parity_mark_sectors_error(sblock->sparity,
+						start, end - start);
+	}
+}
+
+static void drop_csum_range(struct scrub_ctx *sctx, struct btrfs_ordered_sum *sum)
+{
+	sctx->stat.csum_discards += sum->len >> sctx->fs_info->sectorsize_bits;
+	list_del(&sum->list);
+	kfree(sum);
+}
+
+/*
+ * Find the desired csum for range [logical, logical + sectorsize), and store
+ * the csum into @csum.
+ *
+ * The search source is sctx->csum_list, which is a pre-populated list
+ * storing bytenr ordered csum ranges.  We're responsible to cleanup any range
+ * that is before @logical.
+ *
+ * Return 0 if there is no csum for the range.
+ * Return 1 if there is csum for the range and copied to @csum.
+ */
+static int scrub_find_csum(struct scrub_ctx *sctx, u64 logical, u8 *csum)
+{
+	bool found = false;
+
+	while (!list_empty(&sctx->csum_list)) {
+		struct btrfs_ordered_sum *sum = NULL;
+		unsigned long index;
+		unsigned long num_sectors;
+
+		sum = list_first_entry(&sctx->csum_list,
+				       struct btrfs_ordered_sum, list);
+		/* The current csum range is beyond our range, no csum found */
+		if (sum->bytenr > logical)
+			break;
+
+		/*
+		 * The current sum is before our bytenr, since scrub is always
+		 * done in bytenr order, the csum will never be used anymore,
+		 * clean it up so that later calls won't bother with the range,
+		 * and continue search the next range.
+		 */
+		if (sum->bytenr + sum->len <= logical) {
+			drop_csum_range(sctx, sum);
+			continue;
+		}
+
+		/* Now the csum range covers our bytenr, copy the csum */
+		found = true;
+		index = (logical - sum->bytenr) >> sctx->fs_info->sectorsize_bits;
+		num_sectors = sum->len >> sctx->fs_info->sectorsize_bits;
+
+		memcpy(csum, sum->sums + index * sctx->fs_info->csum_size,
+		       sctx->fs_info->csum_size);
+
+		/* Cleanup the range if we're at the end of the csum range */
+		if (index == num_sectors - 1)
+			drop_csum_range(sctx, sum);
+		break;
+	}
+	if (!found)
+		return 0;
+	return 1;
+}
+
+/* scrub extent tries to collect up to 64 kB for each bio */
+static int scrub_extent(struct scrub_ctx *sctx, struct map_lookup *map,
+			u64 logical, u32 len,
+			u64 physical, struct btrfs_device *dev, u64 flags,
+			u64 gen, int mirror_num)
+{
+	struct btrfs_device *src_dev = dev;
+	u64 src_physical = physical;
+	int src_mirror = mirror_num;
+	int ret;
+	u8 csum[BTRFS_CSUM_SIZE];
+	u32 blocksize;
+
+	if (flags & BTRFS_EXTENT_FLAG_DATA) {
+		if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK)
+			blocksize = map->stripe_len;
+		else
+			blocksize = sctx->fs_info->sectorsize;
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.data_extents_scrubbed++;
+		sctx->stat.data_bytes_scrubbed += len;
+		spin_unlock(&sctx->stat_lock);
+	} else if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
+		if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK)
+			blocksize = map->stripe_len;
+		else
+			blocksize = sctx->fs_info->nodesize;
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.tree_extents_scrubbed++;
+		sctx->stat.tree_bytes_scrubbed += len;
+		spin_unlock(&sctx->stat_lock);
+	} else {
+		blocksize = sctx->fs_info->sectorsize;
+		WARN_ON(1);
+	}
+
+	/*
+	 * For dev-replace case, we can have @dev being a missing device.
+	 * Regular scrub will avoid its execution on missing device at all,
+	 * as that would trigger tons of read error.
+	 *
+	 * Reading from missing device will cause read error counts to
+	 * increase unnecessarily.
+	 * So here we change the read source to a good mirror.
+	 */
+	if (sctx->is_dev_replace && !dev->bdev)
+		scrub_find_good_copy(sctx->fs_info, logical, len, &src_physical,
+				     &src_dev, &src_mirror);
+	while (len) {
+		u32 l = min(len, blocksize);
+		int have_csum = 0;
+
+		if (flags & BTRFS_EXTENT_FLAG_DATA) {
+			/* push csums to sbio */
+			have_csum = scrub_find_csum(sctx, logical, csum);
+			if (have_csum == 0)
+				++sctx->stat.no_csum;
+		}
+		ret = scrub_sectors(sctx, logical, l, src_physical, src_dev,
+				    flags, gen, src_mirror,
+				    have_csum ? csum : NULL, physical);
+		if (ret)
+			return ret;
+		len -= l;
+		logical += l;
+		physical += l;
+		src_physical += l;
+	}
+	return 0;
+}
+
+static int scrub_sectors_for_parity(struct scrub_parity *sparity,
+				  u64 logical, u32 len,
+				  u64 physical, struct btrfs_device *dev,
+				  u64 flags, u64 gen, int mirror_num, u8 *csum)
+{
+	struct scrub_ctx *sctx = sparity->sctx;
+	struct scrub_block *sblock;
+	const u32 sectorsize = sctx->fs_info->sectorsize;
+	int index;
+
+	ASSERT(IS_ALIGNED(len, sectorsize));
+
+	sblock = alloc_scrub_block(sctx, dev, logical, physical, physical, mirror_num);
+	if (!sblock) {
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.malloc_errors++;
+		spin_unlock(&sctx->stat_lock);
+		return -ENOMEM;
+	}
+
+	sblock->sparity = sparity;
+	scrub_parity_get(sparity);
+
+	for (index = 0; len > 0; index++) {
+		struct scrub_sector *sector;
+
+		sector = alloc_scrub_sector(sblock, logical, GFP_KERNEL);
+		if (!sector) {
+			spin_lock(&sctx->stat_lock);
+			sctx->stat.malloc_errors++;
+			spin_unlock(&sctx->stat_lock);
+			scrub_block_put(sblock);
+			return -ENOMEM;
+		}
+		sblock->sectors[index] = sector;
+		/* For scrub parity */
+		scrub_sector_get(sector);
+		list_add_tail(&sector->list, &sparity->sectors_list);
+		sector->flags = flags;
+		sector->generation = gen;
+		if (csum) {
+			sector->have_csum = 1;
+			memcpy(sector->csum, csum, sctx->fs_info->csum_size);
+		} else {
+			sector->have_csum = 0;
+		}
+
+		/* Iterate over the stripe range in sectorsize steps */
+		len -= sectorsize;
+		logical += sectorsize;
+		physical += sectorsize;
+	}
+
+	WARN_ON(sblock->sector_count == 0);
+	for (index = 0; index < sblock->sector_count; index++) {
+		struct scrub_sector *sector = sblock->sectors[index];
+		int ret;
+
+		ret = scrub_add_sector_to_rd_bio(sctx, sector);
+		if (ret) {
+			scrub_block_put(sblock);
+			return ret;
+		}
+	}
+
+	/* Last one frees, either here or in bio completion for last sector */
+	scrub_block_put(sblock);
+	return 0;
+}
+
+static int scrub_extent_for_parity(struct scrub_parity *sparity,
+				   u64 logical, u32 len,
+				   u64 physical, struct btrfs_device *dev,
+				   u64 flags, u64 gen, int mirror_num)
+{
+	struct scrub_ctx *sctx = sparity->sctx;
+	int ret;
+	u8 csum[BTRFS_CSUM_SIZE];
+	u32 blocksize;
+
+	if (test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state)) {
+		scrub_parity_mark_sectors_error(sparity, logical, len);
+		return 0;
+	}
+
+	if (flags & BTRFS_EXTENT_FLAG_DATA) {
+		blocksize = sparity->stripe_len;
+	} else if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
+		blocksize = sparity->stripe_len;
+	} else {
+		blocksize = sctx->fs_info->sectorsize;
+		WARN_ON(1);
+	}
+
+	while (len) {
+		u32 l = min(len, blocksize);
+		int have_csum = 0;
+
+		if (flags & BTRFS_EXTENT_FLAG_DATA) {
+			/* push csums to sbio */
+			have_csum = scrub_find_csum(sctx, logical, csum);
+			if (have_csum == 0)
+				goto skip;
+		}
+		ret = scrub_sectors_for_parity(sparity, logical, l, physical, dev,
+					     flags, gen, mirror_num,
+					     have_csum ? csum : NULL);
+		if (ret)
+			return ret;
+skip:
+		len -= l;
+		logical += l;
+		physical += l;
+	}
+	return 0;
+}
+
+/*
+ * Given a physical address, this will calculate it's
+ * logical offset. if this is a parity stripe, it will return
+ * the most left data stripe's logical offset.
+ *
+ * return 0 if it is a data stripe, 1 means parity stripe.
+ */
+static int get_raid56_logic_offset(u64 physical, int num,
+				   struct map_lookup *map, u64 *offset,
+				   u64 *stripe_start)
+{
+	int i;
+	int j = 0;
+	u64 stripe_nr;
+	u64 last_offset;
+	u32 stripe_index;
+	u32 rot;
+	const int data_stripes = nr_data_stripes(map);
+
+	last_offset = (physical - map->stripes[num].physical) * data_stripes;
+	if (stripe_start)
+		*stripe_start = last_offset;
+
+	*offset = last_offset;
+	for (i = 0; i < data_stripes; i++) {
+		*offset = last_offset + i * map->stripe_len;
+
+		stripe_nr = div64_u64(*offset, map->stripe_len);
+		stripe_nr = div_u64(stripe_nr, data_stripes);
+
+		/* Work out the disk rotation on this stripe-set */
+		stripe_nr = div_u64_rem(stripe_nr, map->num_stripes, &rot);
+		/* calculate which stripe this data locates */
+		rot += i;
+		stripe_index = rot % map->num_stripes;
+		if (stripe_index == num)
+			return 0;
+		if (stripe_index < num)
+			j++;
+	}
+	*offset = last_offset + j * map->stripe_len;
+	return 1;
+}
+
+static void scrub_free_parity(struct scrub_parity *sparity)
+{
+	struct scrub_ctx *sctx = sparity->sctx;
+	struct scrub_sector *curr, *next;
+	int nbits;
+
+	nbits = bitmap_weight(&sparity->ebitmap, sparity->nsectors);
+	if (nbits) {
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.read_errors += nbits;
+		sctx->stat.uncorrectable_errors += nbits;
+		spin_unlock(&sctx->stat_lock);
+	}
+
+	list_for_each_entry_safe(curr, next, &sparity->sectors_list, list) {
+		list_del_init(&curr->list);
+		scrub_sector_put(curr);
+	}
+
+	kfree(sparity);
+}
+
+static void scrub_parity_bio_endio_worker(struct work_struct *work)
+{
+	struct scrub_parity *sparity = container_of(work, struct scrub_parity,
+						    work);
+	struct scrub_ctx *sctx = sparity->sctx;
+
+	btrfs_bio_counter_dec(sctx->fs_info);
+	scrub_free_parity(sparity);
+	scrub_pending_bio_dec(sctx);
+}
+
+static void scrub_parity_bio_endio(struct bio *bio)
+{
+	struct scrub_parity *sparity = bio->bi_private;
+	struct btrfs_fs_info *fs_info = sparity->sctx->fs_info;
+
+	if (bio->bi_status)
+		bitmap_or(&sparity->ebitmap, &sparity->ebitmap,
+			  &sparity->dbitmap, sparity->nsectors);
+
+	bio_put(bio);
+
+	INIT_WORK(&sparity->work, scrub_parity_bio_endio_worker);
+	queue_work(fs_info->scrub_parity_workers, &sparity->work);
+}
+
+static void scrub_parity_check_and_repair(struct scrub_parity *sparity)
+{
+	struct scrub_ctx *sctx = sparity->sctx;
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	struct bio *bio;
+	struct btrfs_raid_bio *rbio;
+	struct btrfs_io_context *bioc = NULL;
+	u64 length;
+	int ret;
+
+	if (!bitmap_andnot(&sparity->dbitmap, &sparity->dbitmap,
+			   &sparity->ebitmap, sparity->nsectors))
+		goto out;
+
+	length = sparity->logic_end - sparity->logic_start;
+
+	btrfs_bio_counter_inc_blocked(fs_info);
+	ret = btrfs_map_sblock(fs_info, BTRFS_MAP_WRITE, sparity->logic_start,
+			       &length, &bioc);
+	if (ret || !bioc || !bioc->raid_map)
+		goto bioc_out;
+
+	bio = bio_alloc(NULL, BIO_MAX_VECS, REQ_OP_READ, GFP_NOFS);
+	bio->bi_iter.bi_sector = sparity->logic_start >> 9;
+	bio->bi_private = sparity;
+	bio->bi_end_io = scrub_parity_bio_endio;
+
+	rbio = raid56_parity_alloc_scrub_rbio(bio, bioc,
+					      sparity->scrub_dev,
+					      &sparity->dbitmap,
+					      sparity->nsectors);
+	btrfs_put_bioc(bioc);
+	if (!rbio)
+		goto rbio_out;
+
+	scrub_pending_bio_inc(sctx);
+	raid56_parity_submit_scrub_rbio(rbio);
+	return;
+
+rbio_out:
+	bio_put(bio);
+bioc_out:
+	btrfs_bio_counter_dec(fs_info);
+	bitmap_or(&sparity->ebitmap, &sparity->ebitmap, &sparity->dbitmap,
+		  sparity->nsectors);
+	spin_lock(&sctx->stat_lock);
+	sctx->stat.malloc_errors++;
+	spin_unlock(&sctx->stat_lock);
+out:
+	scrub_free_parity(sparity);
+}
+
+static void scrub_parity_get(struct scrub_parity *sparity)
+{
+	refcount_inc(&sparity->refs);
+}
+
+static void scrub_parity_put(struct scrub_parity *sparity)
+{
+	if (!refcount_dec_and_test(&sparity->refs))
+		return;
+
+	scrub_parity_check_and_repair(sparity);
+}
+
+/*
+ * Return 0 if the extent item range covers any byte of the range.
+ * Return <0 if the extent item is before @search_start.
+ * Return >0 if the extent item is after @start_start + @search_len.
+ */
+static int compare_extent_item_range(struct btrfs_path *path,
+				     u64 search_start, u64 search_len)
+{
+	struct btrfs_fs_info *fs_info = path->nodes[0]->fs_info;
+	u64 len;
+	struct btrfs_key key;
+
+	btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+	ASSERT(key.type == BTRFS_EXTENT_ITEM_KEY ||
+	       key.type == BTRFS_METADATA_ITEM_KEY);
+	if (key.type == BTRFS_METADATA_ITEM_KEY)
+		len = fs_info->nodesize;
+	else
+		len = key.offset;
+
+	if (key.objectid + len <= search_start)
+		return -1;
+	if (key.objectid >= search_start + search_len)
+		return 1;
+	return 0;
+}
+
+/*
+ * Locate one extent item which covers any byte in range
+ * [@search_start, @search_start + @search_length)
+ *
+ * If the path is not initialized, we will initialize the search by doing
+ * a btrfs_search_slot().
+ * If the path is already initialized, we will use the path as the initial
+ * slot, to avoid duplicated btrfs_search_slot() calls.
+ *
+ * NOTE: If an extent item starts before @search_start, we will still
+ * return the extent item. This is for data extent crossing stripe boundary.
+ *
+ * Return 0 if we found such extent item, and @path will point to the extent item.
+ * Return >0 if no such extent item can be found, and @path will be released.
+ * Return <0 if hit fatal error, and @path will be released.
+ */
+static int find_first_extent_item(struct btrfs_root *extent_root,
+				  struct btrfs_path *path,
+				  u64 search_start, u64 search_len)
+{
+	struct btrfs_fs_info *fs_info = extent_root->fs_info;
+	struct btrfs_key key;
+	int ret;
+
+	/* Continue using the existing path */
+	if (path->nodes[0])
+		goto search_forward;
+
+	if (btrfs_fs_incompat(fs_info, SKINNY_METADATA))
+		key.type = BTRFS_METADATA_ITEM_KEY;
+	else
+		key.type = BTRFS_EXTENT_ITEM_KEY;
+	key.objectid = search_start;
+	key.offset = (u64)-1;
+
+	ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
+	if (ret < 0)
+		return ret;
+
+	ASSERT(ret > 0);
+	/*
+	 * Here we intentionally pass 0 as @min_objectid, as there could be
+	 * an extent item starting before @search_start.
+	 */
+	ret = btrfs_previous_extent_item(extent_root, path, 0);
+	if (ret < 0)
+		return ret;
+	/*
+	 * No matter whether we have found an extent item, the next loop will
+	 * properly do every check on the key.
+	 */
+search_forward:
+	while (true) {
+		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+		if (key.objectid >= search_start + search_len)
+			break;
+		if (key.type != BTRFS_METADATA_ITEM_KEY &&
+		    key.type != BTRFS_EXTENT_ITEM_KEY)
+			goto next;
+
+		ret = compare_extent_item_range(path, search_start, search_len);
+		if (ret == 0)
+			return ret;
+		if (ret > 0)
+			break;
+next:
+		path->slots[0]++;
+		if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
+			ret = btrfs_next_leaf(extent_root, path);
+			if (ret) {
+				/* Either no more item or fatal error */
+				btrfs_release_path(path);
+				return ret;
+			}
+		}
+	}
+	btrfs_release_path(path);
+	return 1;
+}
+
+static void get_extent_info(struct btrfs_path *path, u64 *extent_start_ret,
+			    u64 *size_ret, u64 *flags_ret, u64 *generation_ret)
+{
+	struct btrfs_key key;
+	struct btrfs_extent_item *ei;
+
+	btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+	ASSERT(key.type == BTRFS_METADATA_ITEM_KEY ||
+	       key.type == BTRFS_EXTENT_ITEM_KEY);
+	*extent_start_ret = key.objectid;
+	if (key.type == BTRFS_METADATA_ITEM_KEY)
+		*size_ret = path->nodes[0]->fs_info->nodesize;
+	else
+		*size_ret = key.offset;
+	ei = btrfs_item_ptr(path->nodes[0], path->slots[0], struct btrfs_extent_item);
+	*flags_ret = btrfs_extent_flags(path->nodes[0], ei);
+	*generation_ret = btrfs_extent_generation(path->nodes[0], ei);
+}
+
+static bool does_range_cross_boundary(u64 extent_start, u64 extent_len,
+				      u64 boundary_start, u64 boudary_len)
+{
+	return (extent_start < boundary_start &&
+		extent_start + extent_len > boundary_start) ||
+	       (extent_start < boundary_start + boudary_len &&
+		extent_start + extent_len > boundary_start + boudary_len);
+}
+
+static int scrub_raid56_data_stripe_for_parity(struct scrub_ctx *sctx,
+					       struct scrub_parity *sparity,
+					       struct map_lookup *map,
+					       struct btrfs_device *sdev,
+					       struct btrfs_path *path,
+					       u64 logical)
+{
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	struct btrfs_root *extent_root = btrfs_extent_root(fs_info, logical);
+	struct btrfs_root *csum_root = btrfs_csum_root(fs_info, logical);
+	u64 cur_logical = logical;
+	int ret;
+
+	ASSERT(map->type & BTRFS_BLOCK_GROUP_RAID56_MASK);
+
+	/* Path must not be populated */
+	ASSERT(!path->nodes[0]);
+
+	while (cur_logical < logical + map->stripe_len) {
+		struct btrfs_io_context *bioc = NULL;
+		struct btrfs_device *extent_dev;
+		u64 extent_start;
+		u64 extent_size;
+		u64 mapped_length;
+		u64 extent_flags;
+		u64 extent_gen;
+		u64 extent_physical;
+		u64 extent_mirror_num;
+
+		ret = find_first_extent_item(extent_root, path, cur_logical,
+					     logical + map->stripe_len - cur_logical);
+		/* No more extent item in this data stripe */
+		if (ret > 0) {
+			ret = 0;
+			break;
+		}
+		if (ret < 0)
+			break;
+		get_extent_info(path, &extent_start, &extent_size, &extent_flags,
+				&extent_gen);
+
+		/* Metadata should not cross stripe boundaries */
+		if ((extent_flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) &&
+		    does_range_cross_boundary(extent_start, extent_size,
+					      logical, map->stripe_len)) {
+			btrfs_err(fs_info,
+	"scrub: tree block %llu spanning stripes, ignored. logical=%llu",
+				  extent_start, logical);
+			spin_lock(&sctx->stat_lock);
+			sctx->stat.uncorrectable_errors++;
+			spin_unlock(&sctx->stat_lock);
+			cur_logical += extent_size;
+			continue;
+		}
+
+		/* Skip hole range which doesn't have any extent */
+		cur_logical = max(extent_start, cur_logical);
+
+		/* Truncate the range inside this data stripe */
+		extent_size = min(extent_start + extent_size,
+				  logical + map->stripe_len) - cur_logical;
+		extent_start = cur_logical;
+		ASSERT(extent_size <= U32_MAX);
+
+		scrub_parity_mark_sectors_data(sparity, extent_start, extent_size);
+
+		mapped_length = extent_size;
+		ret = btrfs_map_block(fs_info, BTRFS_MAP_READ, extent_start,
+				      &mapped_length, &bioc, 0);
+		if (!ret && (!bioc || mapped_length < extent_size))
+			ret = -EIO;
+		if (ret) {
+			btrfs_put_bioc(bioc);
+			scrub_parity_mark_sectors_error(sparity, extent_start,
+							extent_size);
+			break;
+		}
+		extent_physical = bioc->stripes[0].physical;
+		extent_mirror_num = bioc->mirror_num;
+		extent_dev = bioc->stripes[0].dev;
+		btrfs_put_bioc(bioc);
+
+		ret = btrfs_lookup_csums_range(csum_root, extent_start,
+					       extent_start + extent_size - 1,
+					       &sctx->csum_list, 1, false);
+		if (ret) {
+			scrub_parity_mark_sectors_error(sparity, extent_start,
+							extent_size);
+			break;
+		}
+
+		ret = scrub_extent_for_parity(sparity, extent_start,
+					      extent_size, extent_physical,
+					      extent_dev, extent_flags,
+					      extent_gen, extent_mirror_num);
+		scrub_free_csums(sctx);
+
+		if (ret) {
+			scrub_parity_mark_sectors_error(sparity, extent_start,
+							extent_size);
+			break;
+		}
+
+		cond_resched();
+		cur_logical += extent_size;
+	}
+	btrfs_release_path(path);
+	return ret;
+}
+
+static noinline_for_stack int scrub_raid56_parity(struct scrub_ctx *sctx,
+						  struct map_lookup *map,
+						  struct btrfs_device *sdev,
+						  u64 logic_start,
+						  u64 logic_end)
+{
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	struct btrfs_path *path;
+	u64 cur_logical;
+	int ret;
+	struct scrub_parity *sparity;
+	int nsectors;
+
+	path = btrfs_alloc_path();
+	if (!path) {
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.malloc_errors++;
+		spin_unlock(&sctx->stat_lock);
+		return -ENOMEM;
+	}
+	path->search_commit_root = 1;
+	path->skip_locking = 1;
+
+	ASSERT(map->stripe_len <= U32_MAX);
+	nsectors = map->stripe_len >> fs_info->sectorsize_bits;
+	ASSERT(nsectors <= BITS_PER_LONG);
+	sparity = kzalloc(sizeof(struct scrub_parity), GFP_NOFS);
+	if (!sparity) {
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.malloc_errors++;
+		spin_unlock(&sctx->stat_lock);
+		btrfs_free_path(path);
+		return -ENOMEM;
+	}
+
+	ASSERT(map->stripe_len <= U32_MAX);
+	sparity->stripe_len = map->stripe_len;
+	sparity->nsectors = nsectors;
+	sparity->sctx = sctx;
+	sparity->scrub_dev = sdev;
+	sparity->logic_start = logic_start;
+	sparity->logic_end = logic_end;
+	refcount_set(&sparity->refs, 1);
+	INIT_LIST_HEAD(&sparity->sectors_list);
+
+	ret = 0;
+	for (cur_logical = logic_start; cur_logical < logic_end;
+	     cur_logical += map->stripe_len) {
+		ret = scrub_raid56_data_stripe_for_parity(sctx, sparity, map,
+							  sdev, path, cur_logical);
+		if (ret < 0)
+			break;
+	}
+
+	scrub_parity_put(sparity);
+	scrub_submit(sctx);
+	mutex_lock(&sctx->wr_lock);
+	scrub_wr_submit(sctx);
+	mutex_unlock(&sctx->wr_lock);
+
+	btrfs_free_path(path);
+	return ret < 0 ? ret : 0;
+}
+
+static void sync_replace_for_zoned(struct scrub_ctx *sctx)
+{
+	if (!btrfs_is_zoned(sctx->fs_info))
+		return;
+
+	sctx->flush_all_writes = true;
+	scrub_submit(sctx);
+	mutex_lock(&sctx->wr_lock);
+	scrub_wr_submit(sctx);
+	mutex_unlock(&sctx->wr_lock);
+
+	wait_event(sctx->list_wait, atomic_read(&sctx->bios_in_flight) == 0);
+}
+
+static int sync_write_pointer_for_zoned(struct scrub_ctx *sctx, u64 logical,
+					u64 physical, u64 physical_end)
+{
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	int ret = 0;
+
+	if (!btrfs_is_zoned(fs_info))
+		return 0;
+
+	wait_event(sctx->list_wait, atomic_read(&sctx->bios_in_flight) == 0);
+
+	mutex_lock(&sctx->wr_lock);
+	if (sctx->write_pointer < physical_end) {
+		ret = btrfs_sync_zone_write_pointer(sctx->wr_tgtdev, logical,
+						    physical,
+						    sctx->write_pointer);
+		if (ret)
+			btrfs_err(fs_info,
+				  "zoned: failed to recover write pointer");
+	}
+	mutex_unlock(&sctx->wr_lock);
+	btrfs_dev_clear_zone_empty(sctx->wr_tgtdev, physical);
+
+	return ret;
+}
+
+/*
+ * Scrub one range which can only has simple mirror based profile.
+ * (Including all range in SINGLE/DUP/RAID1/RAID1C*, and each stripe in
+ *  RAID0/RAID10).
+ *
+ * Since we may need to handle a subset of block group, we need @logical_start
+ * and @logical_length parameter.
+ */
+static int scrub_simple_mirror(struct scrub_ctx *sctx,
+			       struct btrfs_root *extent_root,
+			       struct btrfs_root *csum_root,
+			       struct btrfs_block_group *bg,
+			       struct map_lookup *map,
+			       u64 logical_start, u64 logical_length,
+			       struct btrfs_device *device,
+			       u64 physical, int mirror_num)
+{
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	const u64 logical_end = logical_start + logical_length;
+	/* An artificial limit, inherit from old scrub behavior */
+	const u32 max_length = SZ_64K;
+	struct btrfs_path path = { 0 };
+	u64 cur_logical = logical_start;
+	int ret;
+
+	/* The range must be inside the bg */
+	ASSERT(logical_start >= bg->start && logical_end <= bg->start + bg->length);
+
+	path.search_commit_root = 1;
+	path.skip_locking = 1;
+	/* Go through each extent items inside the logical range */
+	while (cur_logical < logical_end) {
+		u64 extent_start;
+		u64 extent_len;
+		u64 extent_flags;
+		u64 extent_gen;
+		u64 scrub_len;
+
+		/* Canceled? */
+		if (atomic_read(&fs_info->scrub_cancel_req) ||
+		    atomic_read(&sctx->cancel_req)) {
+			ret = -ECANCELED;
+			break;
+		}
+		/* Paused? */
+		if (atomic_read(&fs_info->scrub_pause_req)) {
+			/* Push queued extents */
+			sctx->flush_all_writes = true;
+			scrub_submit(sctx);
+			mutex_lock(&sctx->wr_lock);
+			scrub_wr_submit(sctx);
+			mutex_unlock(&sctx->wr_lock);
+			wait_event(sctx->list_wait,
+				   atomic_read(&sctx->bios_in_flight) == 0);
+			sctx->flush_all_writes = false;
+			scrub_blocked_if_needed(fs_info);
+		}
+		/* Block group removed? */
+		spin_lock(&bg->lock);
+		if (test_bit(BLOCK_GROUP_FLAG_REMOVED, &bg->runtime_flags)) {
+			spin_unlock(&bg->lock);
+			ret = 0;
+			break;
+		}
+		spin_unlock(&bg->lock);
+
+		ret = find_first_extent_item(extent_root, &path, cur_logical,
+					     logical_end - cur_logical);
+		if (ret > 0) {
+			/* No more extent, just update the accounting */
+			sctx->stat.last_physical = physical + logical_length;
+			ret = 0;
+			break;
+		}
+		if (ret < 0)
+			break;
+		get_extent_info(&path, &extent_start, &extent_len,
+				&extent_flags, &extent_gen);
+		/* Skip hole range which doesn't have any extent */
+		cur_logical = max(extent_start, cur_logical);
+
+		/*
+		 * Scrub len has three limits:
+		 * - Extent size limit
+		 * - Scrub range limit
+		 *   This is especially imporatant for RAID0/RAID10 to reuse
+		 *   this function
+		 * - Max scrub size limit
+		 */
+		scrub_len = min(min(extent_start + extent_len,
+				    logical_end), cur_logical + max_length) -
+			    cur_logical;
+
+		if (extent_flags & BTRFS_EXTENT_FLAG_DATA) {
+			ret = btrfs_lookup_csums_range(csum_root, cur_logical,
+					cur_logical + scrub_len - 1,
+					&sctx->csum_list, 1, false);
+			if (ret)
+				break;
+		}
+		if ((extent_flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) &&
+		    does_range_cross_boundary(extent_start, extent_len,
+					      logical_start, logical_length)) {
+			btrfs_err(fs_info,
+"scrub: tree block %llu spanning boundaries, ignored. boundary=[%llu, %llu)",
+				  extent_start, logical_start, logical_end);
+			spin_lock(&sctx->stat_lock);
+			sctx->stat.uncorrectable_errors++;
+			spin_unlock(&sctx->stat_lock);
+			cur_logical += scrub_len;
+			continue;
+		}
+		ret = scrub_extent(sctx, map, cur_logical, scrub_len,
+				   cur_logical - logical_start + physical,
+				   device, extent_flags, extent_gen,
+				   mirror_num);
+		scrub_free_csums(sctx);
+		if (ret)
+			break;
+		if (sctx->is_dev_replace)
+			sync_replace_for_zoned(sctx);
+		cur_logical += scrub_len;
+		/* Don't hold CPU for too long time */
+		cond_resched();
+	}
+	btrfs_release_path(&path);
+	return ret;
+}
+
+/* Calculate the full stripe length for simple stripe based profiles */
+static u64 simple_stripe_full_stripe_len(const struct map_lookup *map)
+{
+	ASSERT(map->type & (BTRFS_BLOCK_GROUP_RAID0 |
+			    BTRFS_BLOCK_GROUP_RAID10));
+
+	return map->num_stripes / map->sub_stripes * map->stripe_len;
+}
+
+/* Get the logical bytenr for the stripe */
+static u64 simple_stripe_get_logical(struct map_lookup *map,
+				     struct btrfs_block_group *bg,
+				     int stripe_index)
+{
+	ASSERT(map->type & (BTRFS_BLOCK_GROUP_RAID0 |
+			    BTRFS_BLOCK_GROUP_RAID10));
+	ASSERT(stripe_index < map->num_stripes);
+
+	/*
+	 * (stripe_index / sub_stripes) gives how many data stripes we need to
+	 * skip.
+	 */
+	return (stripe_index / map->sub_stripes) * map->stripe_len + bg->start;
+}
+
+/* Get the mirror number for the stripe */
+static int simple_stripe_mirror_num(struct map_lookup *map, int stripe_index)
+{
+	ASSERT(map->type & (BTRFS_BLOCK_GROUP_RAID0 |
+			    BTRFS_BLOCK_GROUP_RAID10));
+	ASSERT(stripe_index < map->num_stripes);
+
+	/* For RAID0, it's fixed to 1, for RAID10 it's 0,1,0,1... */
+	return stripe_index % map->sub_stripes + 1;
+}
+
+static int scrub_simple_stripe(struct scrub_ctx *sctx,
+			       struct btrfs_root *extent_root,
+			       struct btrfs_root *csum_root,
+			       struct btrfs_block_group *bg,
+			       struct map_lookup *map,
+			       struct btrfs_device *device,
+			       int stripe_index)
+{
+	const u64 logical_increment = simple_stripe_full_stripe_len(map);
+	const u64 orig_logical = simple_stripe_get_logical(map, bg, stripe_index);
+	const u64 orig_physical = map->stripes[stripe_index].physical;
+	const int mirror_num = simple_stripe_mirror_num(map, stripe_index);
+	u64 cur_logical = orig_logical;
+	u64 cur_physical = orig_physical;
+	int ret = 0;
+
+	while (cur_logical < bg->start + bg->length) {
+		/*
+		 * Inside each stripe, RAID0 is just SINGLE, and RAID10 is
+		 * just RAID1, so we can reuse scrub_simple_mirror() to scrub
+		 * this stripe.
+		 */
+		ret = scrub_simple_mirror(sctx, extent_root, csum_root, bg, map,
+					  cur_logical, map->stripe_len, device,
+					  cur_physical, mirror_num);
+		if (ret)
+			return ret;
+		/* Skip to next stripe which belongs to the target device */
+		cur_logical += logical_increment;
+		/* For physical offset, we just go to next stripe */
+		cur_physical += map->stripe_len;
+	}
+	return ret;
+}
+
+static noinline_for_stack int scrub_stripe(struct scrub_ctx *sctx,
+					   struct btrfs_block_group *bg,
+					   struct extent_map *em,
+					   struct btrfs_device *scrub_dev,
+					   int stripe_index)
+{
+	struct btrfs_path *path;
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	struct btrfs_root *root;
+	struct btrfs_root *csum_root;
+	struct blk_plug plug;
+	struct map_lookup *map = em->map_lookup;
+	const u64 profile = map->type & BTRFS_BLOCK_GROUP_PROFILE_MASK;
+	const u64 chunk_logical = bg->start;
+	int ret;
+	u64 physical = map->stripes[stripe_index].physical;
+	const u64 dev_stripe_len = btrfs_calc_stripe_length(em);
+	const u64 physical_end = physical + dev_stripe_len;
+	u64 logical;
+	u64 logic_end;
+	/* The logical increment after finishing one stripe */
+	u64 increment;
+	/* Offset inside the chunk */
+	u64 offset;
+	u64 stripe_logical;
+	u64 stripe_end;
+	int stop_loop = 0;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	/*
+	 * work on commit root. The related disk blocks are static as
+	 * long as COW is applied. This means, it is save to rewrite
+	 * them to repair disk errors without any race conditions
+	 */
+	path->search_commit_root = 1;
+	path->skip_locking = 1;
+	path->reada = READA_FORWARD;
+
+	wait_event(sctx->list_wait,
+		   atomic_read(&sctx->bios_in_flight) == 0);
+	scrub_blocked_if_needed(fs_info);
+
+	root = btrfs_extent_root(fs_info, bg->start);
+	csum_root = btrfs_csum_root(fs_info, bg->start);
+
+	/*
+	 * collect all data csums for the stripe to avoid seeking during
+	 * the scrub. This might currently (crc32) end up to be about 1MB
+	 */
+	blk_start_plug(&plug);
+
+	if (sctx->is_dev_replace &&
+	    btrfs_dev_is_sequential(sctx->wr_tgtdev, physical)) {
+		mutex_lock(&sctx->wr_lock);
+		sctx->write_pointer = physical;
+		mutex_unlock(&sctx->wr_lock);
+		sctx->flush_all_writes = true;
+	}
+
+	/*
+	 * There used to be a big double loop to handle all profiles using the
+	 * same routine, which grows larger and more gross over time.
+	 *
+	 * So here we handle each profile differently, so simpler profiles
+	 * have simpler scrubbing function.
+	 */
+	if (!(profile & (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID10 |
+			 BTRFS_BLOCK_GROUP_RAID56_MASK))) {
+		/*
+		 * Above check rules out all complex profile, the remaining
+		 * profiles are SINGLE|DUP|RAID1|RAID1C*, which is simple
+		 * mirrored duplication without stripe.
+		 *
+		 * Only @physical and @mirror_num needs to calculated using
+		 * @stripe_index.
+		 */
+		ret = scrub_simple_mirror(sctx, root, csum_root, bg, map,
+				bg->start, bg->length, scrub_dev,
+				map->stripes[stripe_index].physical,
+				stripe_index + 1);
+		offset = 0;
+		goto out;
+	}
+	if (profile & (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID10)) {
+		ret = scrub_simple_stripe(sctx, root, csum_root, bg, map,
+					  scrub_dev, stripe_index);
+		offset = map->stripe_len * (stripe_index / map->sub_stripes);
+		goto out;
+	}
+
+	/* Only RAID56 goes through the old code */
+	ASSERT(map->type & BTRFS_BLOCK_GROUP_RAID56_MASK);
+	ret = 0;
+
+	/* Calculate the logical end of the stripe */
+	get_raid56_logic_offset(physical_end, stripe_index,
+				map, &logic_end, NULL);
+	logic_end += chunk_logical;
+
+	/* Initialize @offset in case we need to go to out: label */
+	get_raid56_logic_offset(physical, stripe_index, map, &offset, NULL);
+	increment = map->stripe_len * nr_data_stripes(map);
+
+	/*
+	 * Due to the rotation, for RAID56 it's better to iterate each stripe
+	 * using their physical offset.
+	 */
+	while (physical < physical_end) {
+		ret = get_raid56_logic_offset(physical, stripe_index, map,
+					      &logical, &stripe_logical);
+		logical += chunk_logical;
+		if (ret) {
+			/* it is parity strip */
+			stripe_logical += chunk_logical;
+			stripe_end = stripe_logical + increment;
+			ret = scrub_raid56_parity(sctx, map, scrub_dev,
+						  stripe_logical,
+						  stripe_end);
+			if (ret)
+				goto out;
+			goto next;
+		}
+
+		/*
+		 * Now we're at a data stripe, scrub each extents in the range.
+		 *
+		 * At this stage, if we ignore the repair part, inside each data
+		 * stripe it is no different than SINGLE profile.
+		 * We can reuse scrub_simple_mirror() here, as the repair part
+		 * is still based on @mirror_num.
+		 */
+		ret = scrub_simple_mirror(sctx, root, csum_root, bg, map,
+					  logical, map->stripe_len,
+					  scrub_dev, physical, 1);
+		if (ret < 0)
+			goto out;
+next:
+		logical += increment;
+		physical += map->stripe_len;
+		spin_lock(&sctx->stat_lock);
+		if (stop_loop)
+			sctx->stat.last_physical =
+				map->stripes[stripe_index].physical + dev_stripe_len;
+		else
+			sctx->stat.last_physical = physical;
+		spin_unlock(&sctx->stat_lock);
+		if (stop_loop)
+			break;
+	}
+out:
+	/* push queued extents */
+	scrub_submit(sctx);
+	mutex_lock(&sctx->wr_lock);
+	scrub_wr_submit(sctx);
+	mutex_unlock(&sctx->wr_lock);
+
+	blk_finish_plug(&plug);
+	btrfs_free_path(path);
+
+	if (sctx->is_dev_replace && ret >= 0) {
+		int ret2;
+
+		ret2 = sync_write_pointer_for_zoned(sctx,
+				chunk_logical + offset,
+				map->stripes[stripe_index].physical,
+				physical_end);
+		if (ret2)
+			ret = ret2;
+	}
+
+	return ret < 0 ? ret : 0;
+}
+
+static noinline_for_stack int scrub_chunk(struct scrub_ctx *sctx,
+					  struct btrfs_block_group *bg,
+					  struct btrfs_device *scrub_dev,
+					  u64 dev_offset,
+					  u64 dev_extent_len)
+{
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	struct extent_map_tree *map_tree = &fs_info->mapping_tree;
+	struct map_lookup *map;
+	struct extent_map *em;
+	int i;
+	int ret = 0;
+
+	read_lock(&map_tree->lock);
+	em = lookup_extent_mapping(map_tree, bg->start, bg->length);
+	read_unlock(&map_tree->lock);
+
+	if (!em) {
+		/*
+		 * Might have been an unused block group deleted by the cleaner
+		 * kthread or relocation.
+		 */
+		spin_lock(&bg->lock);
+		if (!test_bit(BLOCK_GROUP_FLAG_REMOVED, &bg->runtime_flags))
+			ret = -EINVAL;
+		spin_unlock(&bg->lock);
+
+		return ret;
+	}
+	if (em->start != bg->start)
+		goto out;
+	if (em->len < dev_extent_len)
+		goto out;
+
+	map = em->map_lookup;
+	for (i = 0; i < map->num_stripes; ++i) {
+		if (map->stripes[i].dev->bdev == scrub_dev->bdev &&
+		    map->stripes[i].physical == dev_offset) {
+			ret = scrub_stripe(sctx, bg, em, scrub_dev, i);
+			if (ret)
+				goto out;
+		}
+	}
+out:
+	free_extent_map(em);
+
+	return ret;
+}
+
+static int finish_extent_writes_for_zoned(struct btrfs_root *root,
+					  struct btrfs_block_group *cache)
+{
+	struct btrfs_fs_info *fs_info = cache->fs_info;
+	struct btrfs_trans_handle *trans;
+
+	if (!btrfs_is_zoned(fs_info))
+		return 0;
+
+	btrfs_wait_block_group_reservations(cache);
+	btrfs_wait_nocow_writers(cache);
+	btrfs_wait_ordered_roots(fs_info, U64_MAX, cache->start, cache->length);
+
+	trans = btrfs_join_transaction(root);
+	if (IS_ERR(trans))
+		return PTR_ERR(trans);
+	return btrfs_commit_transaction(trans);
+}
+
+static noinline_for_stack
+int scrub_enumerate_chunks(struct scrub_ctx *sctx,
+			   struct btrfs_device *scrub_dev, u64 start, u64 end)
+{
+	struct btrfs_dev_extent *dev_extent = NULL;
+	struct btrfs_path *path;
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	struct btrfs_root *root = fs_info->dev_root;
+	u64 chunk_offset;
+	int ret = 0;
+	int ro_set;
+	int slot;
+	struct extent_buffer *l;
+	struct btrfs_key key;
+	struct btrfs_key found_key;
+	struct btrfs_block_group *cache;
+	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	path->reada = READA_FORWARD;
+	path->search_commit_root = 1;
+	path->skip_locking = 1;
+
+	key.objectid = scrub_dev->devid;
+	key.offset = 0ull;
+	key.type = BTRFS_DEV_EXTENT_KEY;
+
+	while (1) {
+		u64 dev_extent_len;
+
+		ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+		if (ret < 0)
+			break;
+		if (ret > 0) {
+			if (path->slots[0] >=
+			    btrfs_header_nritems(path->nodes[0])) {
+				ret = btrfs_next_leaf(root, path);
+				if (ret < 0)
+					break;
+				if (ret > 0) {
+					ret = 0;
+					break;
+				}
+			} else {
+				ret = 0;
+			}
+		}
+
+		l = path->nodes[0];
+		slot = path->slots[0];
+
+		btrfs_item_key_to_cpu(l, &found_key, slot);
+
+		if (found_key.objectid != scrub_dev->devid)
+			break;
+
+		if (found_key.type != BTRFS_DEV_EXTENT_KEY)
+			break;
+
+		if (found_key.offset >= end)
+			break;
+
+		if (found_key.offset < key.offset)
+			break;
+
+		dev_extent = btrfs_item_ptr(l, slot, struct btrfs_dev_extent);
+		dev_extent_len = btrfs_dev_extent_length(l, dev_extent);
+
+		if (found_key.offset + dev_extent_len <= start)
+			goto skip;
+
+		chunk_offset = btrfs_dev_extent_chunk_offset(l, dev_extent);
+
+		/*
+		 * get a reference on the corresponding block group to prevent
+		 * the chunk from going away while we scrub it
+		 */
+		cache = btrfs_lookup_block_group(fs_info, chunk_offset);
+
+		/* some chunks are removed but not committed to disk yet,
+		 * continue scrubbing */
+		if (!cache)
+			goto skip;
+
+		ASSERT(cache->start <= chunk_offset);
+		/*
+		 * We are using the commit root to search for device extents, so
+		 * that means we could have found a device extent item from a
+		 * block group that was deleted in the current transaction. The
+		 * logical start offset of the deleted block group, stored at
+		 * @chunk_offset, might be part of the logical address range of
+		 * a new block group (which uses different physical extents).
+		 * In this case btrfs_lookup_block_group() has returned the new
+		 * block group, and its start address is less than @chunk_offset.
+		 *
+		 * We skip such new block groups, because it's pointless to
+		 * process them, as we won't find their extents because we search
+		 * for them using the commit root of the extent tree. For a device
+		 * replace it's also fine to skip it, we won't miss copying them
+		 * to the target device because we have the write duplication
+		 * setup through the regular write path (by btrfs_map_block()),
+		 * and we have committed a transaction when we started the device
+		 * replace, right after setting up the device replace state.
+		 */
+		if (cache->start < chunk_offset) {
+			btrfs_put_block_group(cache);
+			goto skip;
+		}
+
+		if (sctx->is_dev_replace && btrfs_is_zoned(fs_info)) {
+			if (!test_bit(BLOCK_GROUP_FLAG_TO_COPY, &cache->runtime_flags)) {
+				btrfs_put_block_group(cache);
+				goto skip;
+			}
+		}
+
+		/*
+		 * Make sure that while we are scrubbing the corresponding block
+		 * group doesn't get its logical address and its device extents
+		 * reused for another block group, which can possibly be of a
+		 * different type and different profile. We do this to prevent
+		 * false error detections and crashes due to bogus attempts to
+		 * repair extents.
+		 */
+		spin_lock(&cache->lock);
+		if (test_bit(BLOCK_GROUP_FLAG_REMOVED, &cache->runtime_flags)) {
+			spin_unlock(&cache->lock);
+			btrfs_put_block_group(cache);
+			goto skip;
+		}
+		btrfs_freeze_block_group(cache);
+		spin_unlock(&cache->lock);
+
+		/*
+		 * we need call btrfs_inc_block_group_ro() with scrubs_paused,
+		 * to avoid deadlock caused by:
+		 * btrfs_inc_block_group_ro()
+		 * -> btrfs_wait_for_commit()
+		 * -> btrfs_commit_transaction()
+		 * -> btrfs_scrub_pause()
+		 */
+		scrub_pause_on(fs_info);
+
+		/*
+		 * Don't do chunk preallocation for scrub.
+		 *
+		 * This is especially important for SYSTEM bgs, or we can hit
+		 * -EFBIG from btrfs_finish_chunk_alloc() like:
+		 * 1. The only SYSTEM bg is marked RO.
+		 *    Since SYSTEM bg is small, that's pretty common.
+		 * 2. New SYSTEM bg will be allocated
+		 *    Due to regular version will allocate new chunk.
+		 * 3. New SYSTEM bg is empty and will get cleaned up
+		 *    Before cleanup really happens, it's marked RO again.
+		 * 4. Empty SYSTEM bg get scrubbed
+		 *    We go back to 2.
+		 *
+		 * This can easily boost the amount of SYSTEM chunks if cleaner
+		 * thread can't be triggered fast enough, and use up all space
+		 * of btrfs_super_block::sys_chunk_array
+		 *
+		 * While for dev replace, we need to try our best to mark block
+		 * group RO, to prevent race between:
+		 * - Write duplication
+		 *   Contains latest data
+		 * - Scrub copy
+		 *   Contains data from commit tree
+		 *
+		 * If target block group is not marked RO, nocow writes can
+		 * be overwritten by scrub copy, causing data corruption.
+		 * So for dev-replace, it's not allowed to continue if a block
+		 * group is not RO.
+		 */
+		ret = btrfs_inc_block_group_ro(cache, sctx->is_dev_replace);
+		if (!ret && sctx->is_dev_replace) {
+			ret = finish_extent_writes_for_zoned(root, cache);
+			if (ret) {
+				btrfs_dec_block_group_ro(cache);
+				scrub_pause_off(fs_info);
+				btrfs_put_block_group(cache);
+				break;
+			}
+		}
+
+		if (ret == 0) {
+			ro_set = 1;
+		} else if (ret == -ENOSPC && !sctx->is_dev_replace &&
+			   !(cache->flags & BTRFS_BLOCK_GROUP_RAID56_MASK)) {
+			/*
+			 * btrfs_inc_block_group_ro return -ENOSPC when it
+			 * failed in creating new chunk for metadata.
+			 * It is not a problem for scrub, because
+			 * metadata are always cowed, and our scrub paused
+			 * commit_transactions.
+			 *
+			 * For RAID56 chunks, we have to mark them read-only
+			 * for scrub, as later we would use our own cache
+			 * out of RAID56 realm.
+			 * Thus we want the RAID56 bg to be marked RO to
+			 * prevent RMW from screwing up out cache.
+			 */
+			ro_set = 0;
+		} else if (ret == -ETXTBSY) {
+			btrfs_warn(fs_info,
+		   "skipping scrub of block group %llu due to active swapfile",
+				   cache->start);
+			scrub_pause_off(fs_info);
+			ret = 0;
+			goto skip_unfreeze;
+		} else {
+			btrfs_warn(fs_info,
+				   "failed setting block group ro: %d", ret);
+			btrfs_unfreeze_block_group(cache);
+			btrfs_put_block_group(cache);
+			scrub_pause_off(fs_info);
+			break;
+		}
+
+		/*
+		 * Now the target block is marked RO, wait for nocow writes to
+		 * finish before dev-replace.
+		 * COW is fine, as COW never overwrites extents in commit tree.
+		 */
+		if (sctx->is_dev_replace) {
+			btrfs_wait_nocow_writers(cache);
+			btrfs_wait_ordered_roots(fs_info, U64_MAX, cache->start,
+					cache->length);
+		}
+
+		scrub_pause_off(fs_info);
+		down_write(&dev_replace->rwsem);
+		dev_replace->cursor_right = found_key.offset + dev_extent_len;
+		dev_replace->cursor_left = found_key.offset;
+		dev_replace->item_needs_writeback = 1;
+		up_write(&dev_replace->rwsem);
+
+		ret = scrub_chunk(sctx, cache, scrub_dev, found_key.offset,
+				  dev_extent_len);
+
+		/*
+		 * flush, submit all pending read and write bios, afterwards
+		 * wait for them.
+		 * Note that in the dev replace case, a read request causes
+		 * write requests that are submitted in the read completion
+		 * worker. Therefore in the current situation, it is required
+		 * that all write requests are flushed, so that all read and
+		 * write requests are really completed when bios_in_flight
+		 * changes to 0.
+		 */
+		sctx->flush_all_writes = true;
+		scrub_submit(sctx);
+		mutex_lock(&sctx->wr_lock);
+		scrub_wr_submit(sctx);
+		mutex_unlock(&sctx->wr_lock);
+
+		wait_event(sctx->list_wait,
+			   atomic_read(&sctx->bios_in_flight) == 0);
+
+		scrub_pause_on(fs_info);
+
+		/*
+		 * must be called before we decrease @scrub_paused.
+		 * make sure we don't block transaction commit while
+		 * we are waiting pending workers finished.
+		 */
+		wait_event(sctx->list_wait,
+			   atomic_read(&sctx->workers_pending) == 0);
+		sctx->flush_all_writes = false;
+
+		scrub_pause_off(fs_info);
+
+		if (sctx->is_dev_replace &&
+		    !btrfs_finish_block_group_to_copy(dev_replace->srcdev,
+						      cache, found_key.offset))
+			ro_set = 0;
+
+		down_write(&dev_replace->rwsem);
+		dev_replace->cursor_left = dev_replace->cursor_right;
+		dev_replace->item_needs_writeback = 1;
+		up_write(&dev_replace->rwsem);
+
+		if (ro_set)
+			btrfs_dec_block_group_ro(cache);
+
+		/*
+		 * We might have prevented the cleaner kthread from deleting
+		 * this block group if it was already unused because we raced
+		 * and set it to RO mode first. So add it back to the unused
+		 * list, otherwise it might not ever be deleted unless a manual
+		 * balance is triggered or it becomes used and unused again.
+		 */
+		spin_lock(&cache->lock);
+		if (!test_bit(BLOCK_GROUP_FLAG_REMOVED, &cache->runtime_flags) &&
+		    !cache->ro && cache->reserved == 0 && cache->used == 0) {
+			spin_unlock(&cache->lock);
+			if (btrfs_test_opt(fs_info, DISCARD_ASYNC))
+				btrfs_discard_queue_work(&fs_info->discard_ctl,
+							 cache);
+			else
+				btrfs_mark_bg_unused(cache);
+		} else {
+			spin_unlock(&cache->lock);
+		}
+skip_unfreeze:
+		btrfs_unfreeze_block_group(cache);
+		btrfs_put_block_group(cache);
+		if (ret)
+			break;
+		if (sctx->is_dev_replace &&
+		    atomic64_read(&dev_replace->num_write_errors) > 0) {
+			ret = -EIO;
+			break;
+		}
+		if (sctx->stat.malloc_errors > 0) {
+			ret = -ENOMEM;
+			break;
+		}
+skip:
+		key.offset = found_key.offset + dev_extent_len;
+		btrfs_release_path(path);
+	}
+
+	btrfs_free_path(path);
+
+	return ret;
+}
+
+static noinline_for_stack int scrub_supers(struct scrub_ctx *sctx,
+					   struct btrfs_device *scrub_dev)
+{
+	int	i;
+	u64	bytenr;
+	u64	gen;
+	int	ret;
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+
+	if (BTRFS_FS_ERROR(fs_info))
+		return -EROFS;
+
+	/* Seed devices of a new filesystem has their own generation. */
+	if (scrub_dev->fs_devices != fs_info->fs_devices)
+		gen = scrub_dev->generation;
+	else
+		gen = fs_info->last_trans_committed;
+
+	for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
+		bytenr = btrfs_sb_offset(i);
+		if (bytenr + BTRFS_SUPER_INFO_SIZE >
+		    scrub_dev->commit_total_bytes)
+			break;
+		if (!btrfs_check_super_location(scrub_dev, bytenr))
+			continue;
+
+		ret = scrub_sectors(sctx, bytenr, BTRFS_SUPER_INFO_SIZE, bytenr,
+				    scrub_dev, BTRFS_EXTENT_FLAG_SUPER, gen, i,
+				    NULL, bytenr);
+		if (ret)
+			return ret;
+	}
+	wait_event(sctx->list_wait, atomic_read(&sctx->bios_in_flight) == 0);
+
+	return 0;
+}
+
+static void scrub_workers_put(struct btrfs_fs_info *fs_info)
+{
+	if (refcount_dec_and_mutex_lock(&fs_info->scrub_workers_refcnt,
+					&fs_info->scrub_lock)) {
+		struct workqueue_struct *scrub_workers = fs_info->scrub_workers;
+		struct workqueue_struct *scrub_wr_comp =
+						fs_info->scrub_wr_completion_workers;
+		struct workqueue_struct *scrub_parity =
+						fs_info->scrub_parity_workers;
+
+		fs_info->scrub_workers = NULL;
+		fs_info->scrub_wr_completion_workers = NULL;
+		fs_info->scrub_parity_workers = NULL;
+		mutex_unlock(&fs_info->scrub_lock);
+
+		if (scrub_workers)
+			destroy_workqueue(scrub_workers);
+		if (scrub_wr_comp)
+			destroy_workqueue(scrub_wr_comp);
+		if (scrub_parity)
+			destroy_workqueue(scrub_parity);
+	}
+}
+
+/*
+ * get a reference count on fs_info->scrub_workers. start worker if necessary
+ */
+static noinline_for_stack int scrub_workers_get(struct btrfs_fs_info *fs_info,
+						int is_dev_replace)
+{
+	struct workqueue_struct *scrub_workers = NULL;
+	struct workqueue_struct *scrub_wr_comp = NULL;
+	struct workqueue_struct *scrub_parity = NULL;
+	unsigned int flags = WQ_FREEZABLE | WQ_UNBOUND;
+	int max_active = fs_info->thread_pool_size;
+	int ret = -ENOMEM;
+
+	if (refcount_inc_not_zero(&fs_info->scrub_workers_refcnt))
+		return 0;
+
+	scrub_workers = alloc_workqueue("btrfs-scrub", flags,
+					is_dev_replace ? 1 : max_active);
+	if (!scrub_workers)
+		goto fail_scrub_workers;
+
+	scrub_wr_comp = alloc_workqueue("btrfs-scrubwrc", flags, max_active);
+	if (!scrub_wr_comp)
+		goto fail_scrub_wr_completion_workers;
+
+	scrub_parity = alloc_workqueue("btrfs-scrubparity", flags, max_active);
+	if (!scrub_parity)
+		goto fail_scrub_parity_workers;
+
+	mutex_lock(&fs_info->scrub_lock);
+	if (refcount_read(&fs_info->scrub_workers_refcnt) == 0) {
+		ASSERT(fs_info->scrub_workers == NULL &&
+		       fs_info->scrub_wr_completion_workers == NULL &&
+		       fs_info->scrub_parity_workers == NULL);
+		fs_info->scrub_workers = scrub_workers;
+		fs_info->scrub_wr_completion_workers = scrub_wr_comp;
+		fs_info->scrub_parity_workers = scrub_parity;
+		refcount_set(&fs_info->scrub_workers_refcnt, 1);
+		mutex_unlock(&fs_info->scrub_lock);
+		return 0;
+	}
+	/* Other thread raced in and created the workers for us */
+	refcount_inc(&fs_info->scrub_workers_refcnt);
+	mutex_unlock(&fs_info->scrub_lock);
+
+	ret = 0;
+	destroy_workqueue(scrub_parity);
+fail_scrub_parity_workers:
+	destroy_workqueue(scrub_wr_comp);
+fail_scrub_wr_completion_workers:
+	destroy_workqueue(scrub_workers);
+fail_scrub_workers:
+	return ret;
+}
+
+int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
+		    u64 end, struct btrfs_scrub_progress *progress,
+		    int readonly, int is_dev_replace)
+{
+	struct btrfs_dev_lookup_args args = { .devid = devid };
+	struct scrub_ctx *sctx;
+	int ret;
+	struct btrfs_device *dev;
+	unsigned int nofs_flag;
+	bool need_commit = false;
+
+	if (btrfs_fs_closing(fs_info))
+		return -EAGAIN;
+
+	/* At mount time we have ensured nodesize is in the range of [4K, 64K]. */
+	ASSERT(fs_info->nodesize <= BTRFS_STRIPE_LEN);
+
+	/*
+	 * SCRUB_MAX_SECTORS_PER_BLOCK is calculated using the largest possible
+	 * value (max nodesize / min sectorsize), thus nodesize should always
+	 * be fine.
+	 */
+	ASSERT(fs_info->nodesize <=
+	       SCRUB_MAX_SECTORS_PER_BLOCK << fs_info->sectorsize_bits);
+
+	/* Allocate outside of device_list_mutex */
+	sctx = scrub_setup_ctx(fs_info, is_dev_replace);
+	if (IS_ERR(sctx))
+		return PTR_ERR(sctx);
+
+	ret = scrub_workers_get(fs_info, is_dev_replace);
+	if (ret)
+		goto out_free_ctx;
+
+	mutex_lock(&fs_info->fs_devices->device_list_mutex);
+	dev = btrfs_find_device(fs_info->fs_devices, &args);
+	if (!dev || (test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state) &&
+		     !is_dev_replace)) {
+		mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+		ret = -ENODEV;
+		goto out;
+	}
+
+	if (!is_dev_replace && !readonly &&
+	    !test_bit(BTRFS_DEV_STATE_WRITEABLE, &dev->dev_state)) {
+		mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+		btrfs_err_in_rcu(fs_info,
+			"scrub on devid %llu: filesystem on %s is not writable",
+				 devid, rcu_str_deref(dev->name));
+		ret = -EROFS;
+		goto out;
+	}
+
+	mutex_lock(&fs_info->scrub_lock);
+	if (!test_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &dev->dev_state) ||
+	    test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &dev->dev_state)) {
+		mutex_unlock(&fs_info->scrub_lock);
+		mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+		ret = -EIO;
+		goto out;
+	}
+
+	down_read(&fs_info->dev_replace.rwsem);
+	if (dev->scrub_ctx ||
+	    (!is_dev_replace &&
+	     btrfs_dev_replace_is_ongoing(&fs_info->dev_replace))) {
+		up_read(&fs_info->dev_replace.rwsem);
+		mutex_unlock(&fs_info->scrub_lock);
+		mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+		ret = -EINPROGRESS;
+		goto out;
+	}
+	up_read(&fs_info->dev_replace.rwsem);
+
+	sctx->readonly = readonly;
+	dev->scrub_ctx = sctx;
+	mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+
+	/*
+	 * checking @scrub_pause_req here, we can avoid
+	 * race between committing transaction and scrubbing.
+	 */
+	__scrub_blocked_if_needed(fs_info);
+	atomic_inc(&fs_info->scrubs_running);
+	mutex_unlock(&fs_info->scrub_lock);
+
+	/*
+	 * In order to avoid deadlock with reclaim when there is a transaction
+	 * trying to pause scrub, make sure we use GFP_NOFS for all the
+	 * allocations done at btrfs_scrub_sectors() and scrub_sectors_for_parity()
+	 * invoked by our callees. The pausing request is done when the
+	 * transaction commit starts, and it blocks the transaction until scrub
+	 * is paused (done at specific points at scrub_stripe() or right above
+	 * before incrementing fs_info->scrubs_running).
+	 */
+	nofs_flag = memalloc_nofs_save();
+	if (!is_dev_replace) {
+		u64 old_super_errors;
+
+		spin_lock(&sctx->stat_lock);
+		old_super_errors = sctx->stat.super_errors;
+		spin_unlock(&sctx->stat_lock);
+
+		btrfs_info(fs_info, "scrub: started on devid %llu", devid);
+		/*
+		 * by holding device list mutex, we can
+		 * kick off writing super in log tree sync.
+		 */
+		mutex_lock(&fs_info->fs_devices->device_list_mutex);
+		ret = scrub_supers(sctx, dev);
+		mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+
+		spin_lock(&sctx->stat_lock);
+		/*
+		 * Super block errors found, but we can not commit transaction
+		 * at current context, since btrfs_commit_transaction() needs
+		 * to pause the current running scrub (hold by ourselves).
+		 */
+		if (sctx->stat.super_errors > old_super_errors && !sctx->readonly)
+			need_commit = true;
+		spin_unlock(&sctx->stat_lock);
+	}
+
+	if (!ret)
+		ret = scrub_enumerate_chunks(sctx, dev, start, end);
+	memalloc_nofs_restore(nofs_flag);
+
+	wait_event(sctx->list_wait, atomic_read(&sctx->bios_in_flight) == 0);
+	atomic_dec(&fs_info->scrubs_running);
+	wake_up(&fs_info->scrub_pause_wait);
+
+	wait_event(sctx->list_wait, atomic_read(&sctx->workers_pending) == 0);
+
+	if (progress)
+		memcpy(progress, &sctx->stat, sizeof(*progress));
+
+	if (!is_dev_replace)
+		btrfs_info(fs_info, "scrub: %s on devid %llu with status: %d",
+			ret ? "not finished" : "finished", devid, ret);
+
+	mutex_lock(&fs_info->scrub_lock);
+	dev->scrub_ctx = NULL;
+	mutex_unlock(&fs_info->scrub_lock);
+
+	scrub_workers_put(fs_info);
+	scrub_put_ctx(sctx);
+
+	/*
+	 * We found some super block errors before, now try to force a
+	 * transaction commit, as scrub has finished.
+	 */
+	if (need_commit) {
+		struct btrfs_trans_handle *trans;
+
+		trans = btrfs_start_transaction(fs_info->tree_root, 0);
+		if (IS_ERR(trans)) {
+			ret = PTR_ERR(trans);
+			btrfs_err(fs_info,
+	"scrub: failed to start transaction to fix super block errors: %d", ret);
+			return ret;
+		}
+		ret = btrfs_commit_transaction(trans);
+		if (ret < 0)
+			btrfs_err(fs_info,
+	"scrub: failed to commit transaction to fix super block errors: %d", ret);
+	}
+	return ret;
+out:
+	scrub_workers_put(fs_info);
+out_free_ctx:
+	scrub_free_ctx(sctx);
+
+	return ret;
+}
+
+void btrfs_scrub_pause(struct btrfs_fs_info *fs_info)
+{
+	mutex_lock(&fs_info->scrub_lock);
+	atomic_inc(&fs_info->scrub_pause_req);
+	while (atomic_read(&fs_info->scrubs_paused) !=
+	       atomic_read(&fs_info->scrubs_running)) {
+		mutex_unlock(&fs_info->scrub_lock);
+		wait_event(fs_info->scrub_pause_wait,
+			   atomic_read(&fs_info->scrubs_paused) ==
+			   atomic_read(&fs_info->scrubs_running));
+		mutex_lock(&fs_info->scrub_lock);
+	}
+	mutex_unlock(&fs_info->scrub_lock);
+}
+
+void btrfs_scrub_continue(struct btrfs_fs_info *fs_info)
+{
+	atomic_dec(&fs_info->scrub_pause_req);
+	wake_up(&fs_info->scrub_pause_wait);
+}
+
+int btrfs_scrub_cancel(struct btrfs_fs_info *fs_info)
+{
+	mutex_lock(&fs_info->scrub_lock);
+	if (!atomic_read(&fs_info->scrubs_running)) {
+		mutex_unlock(&fs_info->scrub_lock);
+		return -ENOTCONN;
+	}
+
+	atomic_inc(&fs_info->scrub_cancel_req);
+	while (atomic_read(&fs_info->scrubs_running)) {
+		mutex_unlock(&fs_info->scrub_lock);
+		wait_event(fs_info->scrub_pause_wait,
+			   atomic_read(&fs_info->scrubs_running) == 0);
+		mutex_lock(&fs_info->scrub_lock);
+	}
+	atomic_dec(&fs_info->scrub_cancel_req);
+	mutex_unlock(&fs_info->scrub_lock);
+
+	return 0;
+}
+
+int btrfs_scrub_cancel_dev(struct btrfs_device *dev)
+{
+	struct btrfs_fs_info *fs_info = dev->fs_info;
+	struct scrub_ctx *sctx;
+
+	mutex_lock(&fs_info->scrub_lock);
+	sctx = dev->scrub_ctx;
+	if (!sctx) {
+		mutex_unlock(&fs_info->scrub_lock);
+		return -ENOTCONN;
+	}
+	atomic_inc(&sctx->cancel_req);
+	while (dev->scrub_ctx) {
+		mutex_unlock(&fs_info->scrub_lock);
+		wait_event(fs_info->scrub_pause_wait,
+			   dev->scrub_ctx == NULL);
+		mutex_lock(&fs_info->scrub_lock);
+	}
+	mutex_unlock(&fs_info->scrub_lock);
+
+	return 0;
+}
+
+int btrfs_scrub_progress(struct btrfs_fs_info *fs_info, u64 devid,
+			 struct btrfs_scrub_progress *progress)
+{
+	struct btrfs_dev_lookup_args args = { .devid = devid };
+	struct btrfs_device *dev;
+	struct scrub_ctx *sctx = NULL;
+
+	mutex_lock(&fs_info->fs_devices->device_list_mutex);
+	dev = btrfs_find_device(fs_info->fs_devices, &args);
+	if (dev)
+		sctx = dev->scrub_ctx;
+	if (sctx)
+		memcpy(progress, &sctx->stat, sizeof(*progress));
+	mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+
+	return dev ? (sctx ? 0 : -ENOTCONN) : -ENODEV;
+}
+
+static void scrub_find_good_copy(struct btrfs_fs_info *fs_info,
+				 u64 extent_logical, u32 extent_len,
+				 u64 *extent_physical,
+				 struct btrfs_device **extent_dev,
+				 int *extent_mirror_num)
+{
+	u64 mapped_length;
+	struct btrfs_io_context *bioc = NULL;
+	int ret;
+
+	mapped_length = extent_len;
+	ret = btrfs_map_block(fs_info, BTRFS_MAP_READ, extent_logical,
+			      &mapped_length, &bioc, 0);
+	if (ret || !bioc || mapped_length < extent_len ||
+	    !bioc->stripes[0].dev->bdev) {
+		btrfs_put_bioc(bioc);
+		return;
+	}
+
+	*extent_physical = bioc->stripes[0].physical;
+	*extent_mirror_num = bioc->mirror_num;
+	*extent_dev = bioc->stripes[0].dev;
+	btrfs_put_bioc(bioc);
+}