Adding upstream version 6.6.15.upstream/6.6.15

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

1 files changed, 3062 insertions, 0 deletions

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
new file mode 100644
index 0000000000..1e3ff87d04
--- /dev/null
+++ b/fs/btrfs/scrub.c
@@ -0,0 +1,3062 @@
+// 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 "raid56.h"
+#include "block-group.h"
+#include "zoned.h"
+#include "fs.h"
+#include "accessors.h"
+#include "file-item.h"
+#include "scrub.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_ctx;
+
+/*
+ * The following value only influences the performance.
+ *
+ * This detemines how many stripes would be submitted in one go,
+ * which is 512KiB (BTRFS_STRIPE_LEN * SCRUB_STRIPES_PER_GROUP).
+ */
+#define SCRUB_STRIPES_PER_GROUP		8
+
+/*
+ * How many groups we have for each sctx.
+ *
+ * This would be 8M per device, the same value as the old scrub in-flight bios
+ * size limit.
+ */
+#define SCRUB_GROUPS_PER_SCTX		16
+
+#define SCRUB_TOTAL_STRIPES		(SCRUB_GROUPS_PER_SCTX * SCRUB_STRIPES_PER_GROUP)
+
+/*
+ * 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)
+
+/* Represent one sector and its needed info to verify the content. */
+struct scrub_sector_verification {
+	bool is_metadata;
+
+	union {
+		/*
+		 * Csum pointer for data csum verification.  Should point to a
+		 * sector csum inside scrub_stripe::csums.
+		 *
+		 * NULL if this data sector has no csum.
+		 */
+		u8 *csum;
+
+		/*
+		 * Extra info for metadata verification.  All sectors inside a
+		 * tree block share the same generation.
+		 */
+		u64 generation;
+	};
+};
+
+enum scrub_stripe_flags {
+	/* Set when @mirror_num, @dev, @physical and @logical are set. */
+	SCRUB_STRIPE_FLAG_INITIALIZED,
+
+	/* Set when the read-repair is finished. */
+	SCRUB_STRIPE_FLAG_REPAIR_DONE,
+
+	/*
+	 * Set for data stripes if it's triggered from P/Q stripe.
+	 * During such scrub, we should not report errors in data stripes, nor
+	 * update the accounting.
+	 */
+	SCRUB_STRIPE_FLAG_NO_REPORT,
+};
+
+#define SCRUB_STRIPE_PAGES		(BTRFS_STRIPE_LEN / PAGE_SIZE)
+
+/*
+ * Represent one contiguous range with a length of BTRFS_STRIPE_LEN.
+ */
+struct scrub_stripe {
+	struct scrub_ctx *sctx;
+	struct btrfs_block_group *bg;
+
+	struct page *pages[SCRUB_STRIPE_PAGES];
+	struct scrub_sector_verification *sectors;
+
+	struct btrfs_device *dev;
+	u64 logical;
+	u64 physical;
+
+	u16 mirror_num;
+
+	/* Should be BTRFS_STRIPE_LEN / sectorsize. */
+	u16 nr_sectors;
+
+	/*
+	 * How many data/meta extents are in this stripe.  Only for scrub status
+	 * reporting purposes.
+	 */
+	u16 nr_data_extents;
+	u16 nr_meta_extents;
+
+	atomic_t pending_io;
+	wait_queue_head_t io_wait;
+	wait_queue_head_t repair_wait;
+
+	/*
+	 * Indicate the states of the stripe.  Bits are defined in
+	 * scrub_stripe_flags enum.
+	 */
+	unsigned long state;
+
+	/* Indicate which sectors are covered by extent items. */
+	unsigned long extent_sector_bitmap;
+
+	/*
+	 * The errors hit during the initial read of the stripe.
+	 *
+	 * Would be utilized for error reporting and repair.
+	 *
+	 * The remaining init_nr_* records the number of errors hit, only used
+	 * by error reporting.
+	 */
+	unsigned long init_error_bitmap;
+	unsigned int init_nr_io_errors;
+	unsigned int init_nr_csum_errors;
+	unsigned int init_nr_meta_errors;
+
+	/*
+	 * The following error bitmaps are all for the current status.
+	 * Every time we submit a new read, these bitmaps may be updated.
+	 *
+	 * error_bitmap = io_error_bitmap | csum_error_bitmap | meta_error_bitmap;
+	 *
+	 * IO and csum errors can happen for both metadata and data.
+	 */
+	unsigned long error_bitmap;
+	unsigned long io_error_bitmap;
+	unsigned long csum_error_bitmap;
+	unsigned long meta_error_bitmap;
+
+	/* For writeback (repair or replace) error reporting. */
+	unsigned long write_error_bitmap;
+
+	/* Writeback can be concurrent, thus we need to protect the bitmap. */
+	spinlock_t write_error_lock;
+
+	/*
+	 * Checksum for the whole stripe if this stripe is inside a data block
+	 * group.
+	 */
+	u8 *csums;
+
+	struct work_struct work;
+};
+
+struct scrub_ctx {
+	struct scrub_stripe	stripes[SCRUB_TOTAL_STRIPES];
+	struct scrub_stripe	*raid56_data_stripes;
+	struct btrfs_fs_info	*fs_info;
+	struct btrfs_path	extent_path;
+	struct btrfs_path	csum_path;
+	int			first_free;
+	int			cur_stripe;
+	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 mutex            wr_lock;
+	struct btrfs_device     *wr_tgtdev;
+
+	/*
+	 * 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;
+};
+
+static void release_scrub_stripe(struct scrub_stripe *stripe)
+{
+	if (!stripe)
+		return;
+
+	for (int i = 0; i < SCRUB_STRIPE_PAGES; i++) {
+		if (stripe->pages[i])
+			__free_page(stripe->pages[i]);
+		stripe->pages[i] = NULL;
+	}
+	kfree(stripe->sectors);
+	kfree(stripe->csums);
+	stripe->sectors = NULL;
+	stripe->csums = NULL;
+	stripe->sctx = NULL;
+	stripe->state = 0;
+}
+
+static int init_scrub_stripe(struct btrfs_fs_info *fs_info,
+			     struct scrub_stripe *stripe)
+{
+	int ret;
+
+	memset(stripe, 0, sizeof(*stripe));
+
+	stripe->nr_sectors = BTRFS_STRIPE_LEN >> fs_info->sectorsize_bits;
+	stripe->state = 0;
+
+	init_waitqueue_head(&stripe->io_wait);
+	init_waitqueue_head(&stripe->repair_wait);
+	atomic_set(&stripe->pending_io, 0);
+	spin_lock_init(&stripe->write_error_lock);
+
+	ret = btrfs_alloc_page_array(SCRUB_STRIPE_PAGES, stripe->pages);
+	if (ret < 0)
+		goto error;
+
+	stripe->sectors = kcalloc(stripe->nr_sectors,
+				  sizeof(struct scrub_sector_verification),
+				  GFP_KERNEL);
+	if (!stripe->sectors)
+		goto error;
+
+	stripe->csums = kcalloc(BTRFS_STRIPE_LEN >> fs_info->sectorsize_bits,
+				fs_info->csum_size, GFP_KERNEL);
+	if (!stripe->csums)
+		goto error;
+	return 0;
+error:
+	release_scrub_stripe(stripe);
+	return -ENOMEM;
+}
+
+static void wait_scrub_stripe_io(struct scrub_stripe *stripe)
+{
+	wait_event(stripe->io_wait, atomic_read(&stripe->pending_io) == 0);
+}
+
+static void scrub_put_ctx(struct scrub_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);
+}
+
+static noinline_for_stack void scrub_free_ctx(struct scrub_ctx *sctx)
+{
+	int i;
+
+	if (!sctx)
+		return;
+
+	for (i = 0; i < SCRUB_TOTAL_STRIPES; i++)
+		release_scrub_stripe(&sctx->stripes[i]);
+
+	kvfree(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;
+
+	/* Since sctx has inline 128 stripes, it can go beyond 64K easily.  Use
+	 * kvzalloc().
+	 */
+	sctx = kvzalloc(sizeof(*sctx), GFP_KERNEL);
+	if (!sctx)
+		goto nomem;
+	refcount_set(&sctx->refs, 1);
+	sctx->is_dev_replace = is_dev_replace;
+	sctx->fs_info = fs_info;
+	sctx->extent_path.search_commit_root = 1;
+	sctx->extent_path.skip_locking = 1;
+	sctx->csum_path.search_commit_root = 1;
+	sctx->csum_path.skip_locking = 1;
+	for (i = 0; i < SCRUB_TOTAL_STRIPES; i++) {
+		int ret;
+
+		ret = init_scrub_stripe(fs_info, &sctx->stripes[i]);
+		if (ret < 0)
+			goto nomem;
+		sctx->stripes[i].sctx = sctx;
+	}
+	sctx->first_free = 0;
+	atomic_set(&sctx->cancel_req, 0);
+
+	spin_lock_init(&sctx->stat_lock);
+	sctx->throttle_deadline = 0;
+
+	mutex_init(&sctx->wr_lock);
+	if (is_dev_replace) {
+		WARN_ON(!fs_info->dev_replace.tgtdev);
+		sctx->wr_tgtdev = fs_info->dev_replace.tgtdev;
+	}
+
+	return sctx;
+
+nomem:
+	scrub_free_ctx(sctx);
+	return ERR_PTR(-ENOMEM);
+}
+
+static int scrub_print_warning_inode(u64 inum, u64 offset, u64 num_bytes,
+				     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,
+				  btrfs_dev_name(swarn->dev),
+				  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,
+			  btrfs_dev_name(swarn->dev),
+			  swarn->physical,
+			  root, inum, offset, ret);
+
+	free_ipath(ipath);
+	return 0;
+}
+
+static void scrub_print_common_warning(const char *errstr, struct btrfs_device *dev,
+				       bool is_super, u64 logical, u64 physical)
+{
+	struct btrfs_fs_info *fs_info = dev->fs_info;
+	struct btrfs_path *path;
+	struct btrfs_key found_key;
+	struct extent_buffer *eb;
+	struct btrfs_extent_item *ei;
+	struct scrub_warning swarn;
+	u64 flags = 0;
+	u32 item_size;
+	int ret;
+
+	/* Super block error, no need to search extent tree. */
+	if (is_super) {
+		btrfs_warn_in_rcu(fs_info, "%s on device %s, physical %llu",
+				  errstr, btrfs_dev_name(dev), physical);
+		return;
+	}
+	path = btrfs_alloc_path();
+	if (!path)
+		return;
+
+	swarn.physical = physical;
+	swarn.logical = logical;
+	swarn.errstr = errstr;
+	swarn.dev = NULL;
+
+	ret = extent_from_logical(fs_info, swarn.logical, path, &found_key,
+				  &flags);
+	if (ret < 0)
+		goto out;
+
+	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) {
+		unsigned long ptr = 0;
+		u8 ref_level;
+		u64 ref_root;
+
+		while (true) {
+			ret = tree_backref_for_extent(&ptr, eb, &found_key, ei,
+						      item_size, &ref_root,
+						      &ref_level);
+			if (ret < 0) {
+				btrfs_warn(fs_info,
+				"failed to resolve tree backref for logical %llu: %d",
+						  swarn.logical, ret);
+				break;
+			}
+			if (ret > 0)
+				break;
+			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, btrfs_dev_name(dev),
+				swarn.physical, (ref_level ? "node" : "leaf"),
+				ref_level, ref_root);
+		}
+		btrfs_release_path(path);
+	} else {
+		struct btrfs_backref_walk_ctx ctx = { 0 };
+
+		btrfs_release_path(path);
+
+		ctx.bytenr = found_key.objectid;
+		ctx.extent_item_pos = swarn.logical - found_key.objectid;
+		ctx.fs_info = fs_info;
+
+		swarn.path = path;
+		swarn.dev = dev;
+
+		iterate_extent_inodes(&ctx, true, scrub_print_warning_inode, &swarn);
+	}
+
+out:
+	btrfs_free_path(path);
+}
+
+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 struct page *scrub_stripe_get_page(struct scrub_stripe *stripe, int sector_nr)
+{
+	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
+	int page_index = (sector_nr << fs_info->sectorsize_bits) >> PAGE_SHIFT;
+
+	return stripe->pages[page_index];
+}
+
+static unsigned int scrub_stripe_get_page_offset(struct scrub_stripe *stripe,
+						 int sector_nr)
+{
+	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
+
+	return offset_in_page(sector_nr << fs_info->sectorsize_bits);
+}
+
+static void scrub_verify_one_metadata(struct scrub_stripe *stripe, int sector_nr)
+{
+	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
+	const u32 sectors_per_tree = fs_info->nodesize >> fs_info->sectorsize_bits;
+	const u64 logical = stripe->logical + (sector_nr << fs_info->sectorsize_bits);
+	const struct page *first_page = scrub_stripe_get_page(stripe, sector_nr);
+	const unsigned int first_off = scrub_stripe_get_page_offset(stripe, sector_nr);
+	SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
+	u8 on_disk_csum[BTRFS_CSUM_SIZE];
+	u8 calculated_csum[BTRFS_CSUM_SIZE];
+	struct btrfs_header *header;
+
+	/*
+	 * Here we don't have a good way to attach the pages (and subpages)
+	 * to a dummy extent buffer, thus we have to directly grab the members
+	 * from pages.
+	 */
+	header = (struct btrfs_header *)(page_address(first_page) + first_off);
+	memcpy(on_disk_csum, header->csum, fs_info->csum_size);
+
+	if (logical != btrfs_stack_header_bytenr(header)) {
+		bitmap_set(&stripe->csum_error_bitmap, sector_nr, sectors_per_tree);
+		bitmap_set(&stripe->error_bitmap, sector_nr, sectors_per_tree);
+		btrfs_warn_rl(fs_info,
+		"tree block %llu mirror %u has bad bytenr, has %llu want %llu",
+			      logical, stripe->mirror_num,
+			      btrfs_stack_header_bytenr(header), logical);
+		return;
+	}
+	if (memcmp(header->fsid, fs_info->fs_devices->metadata_uuid,
+		   BTRFS_FSID_SIZE) != 0) {
+		bitmap_set(&stripe->meta_error_bitmap, sector_nr, sectors_per_tree);
+		bitmap_set(&stripe->error_bitmap, sector_nr, sectors_per_tree);
+		btrfs_warn_rl(fs_info,
+		"tree block %llu mirror %u has bad fsid, has %pU want %pU",
+			      logical, stripe->mirror_num,
+			      header->fsid, fs_info->fs_devices->fsid);
+		return;
+	}
+	if (memcmp(header->chunk_tree_uuid, fs_info->chunk_tree_uuid,
+		   BTRFS_UUID_SIZE) != 0) {
+		bitmap_set(&stripe->meta_error_bitmap, sector_nr, sectors_per_tree);
+		bitmap_set(&stripe->error_bitmap, sector_nr, sectors_per_tree);
+		btrfs_warn_rl(fs_info,
+		"tree block %llu mirror %u has bad chunk tree uuid, has %pU want %pU",
+			      logical, stripe->mirror_num,
+			      header->chunk_tree_uuid, fs_info->chunk_tree_uuid);
+		return;
+	}
+
+	/* Now check tree block csum. */
+	shash->tfm = fs_info->csum_shash;
+	crypto_shash_init(shash);
+	crypto_shash_update(shash, page_address(first_page) + first_off +
+			    BTRFS_CSUM_SIZE, fs_info->sectorsize - BTRFS_CSUM_SIZE);
+
+	for (int i = sector_nr + 1; i < sector_nr + sectors_per_tree; i++) {
+		struct page *page = scrub_stripe_get_page(stripe, i);
+		unsigned int page_off = scrub_stripe_get_page_offset(stripe, i);
+
+		crypto_shash_update(shash, page_address(page) + page_off,
+				    fs_info->sectorsize);
+	}
+
+	crypto_shash_final(shash, calculated_csum);
+	if (memcmp(calculated_csum, on_disk_csum, fs_info->csum_size) != 0) {
+		bitmap_set(&stripe->meta_error_bitmap, sector_nr, sectors_per_tree);
+		bitmap_set(&stripe->error_bitmap, sector_nr, sectors_per_tree);
+		btrfs_warn_rl(fs_info,
+		"tree block %llu mirror %u has bad csum, has " CSUM_FMT " want " CSUM_FMT,
+			      logical, stripe->mirror_num,
+			      CSUM_FMT_VALUE(fs_info->csum_size, on_disk_csum),
+			      CSUM_FMT_VALUE(fs_info->csum_size, calculated_csum));
+		return;
+	}
+	if (stripe->sectors[sector_nr].generation !=
+	    btrfs_stack_header_generation(header)) {
+		bitmap_set(&stripe->meta_error_bitmap, sector_nr, sectors_per_tree);
+		bitmap_set(&stripe->error_bitmap, sector_nr, sectors_per_tree);
+		btrfs_warn_rl(fs_info,
+		"tree block %llu mirror %u has bad generation, has %llu want %llu",
+			      logical, stripe->mirror_num,
+			      btrfs_stack_header_generation(header),
+			      stripe->sectors[sector_nr].generation);
+		return;
+	}
+	bitmap_clear(&stripe->error_bitmap, sector_nr, sectors_per_tree);
+	bitmap_clear(&stripe->csum_error_bitmap, sector_nr, sectors_per_tree);
+	bitmap_clear(&stripe->meta_error_bitmap, sector_nr, sectors_per_tree);
+}
+
+static void scrub_verify_one_sector(struct scrub_stripe *stripe, int sector_nr)
+{
+	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
+	struct scrub_sector_verification *sector = &stripe->sectors[sector_nr];
+	const u32 sectors_per_tree = fs_info->nodesize >> fs_info->sectorsize_bits;
+	struct page *page = scrub_stripe_get_page(stripe, sector_nr);
+	unsigned int pgoff = scrub_stripe_get_page_offset(stripe, sector_nr);
+	u8 csum_buf[BTRFS_CSUM_SIZE];
+	int ret;
+
+	ASSERT(sector_nr >= 0 && sector_nr < stripe->nr_sectors);
+
+	/* Sector not utilized, skip it. */
+	if (!test_bit(sector_nr, &stripe->extent_sector_bitmap))
+		return;
+
+	/* IO error, no need to check. */
+	if (test_bit(sector_nr, &stripe->io_error_bitmap))
+		return;
+
+	/* Metadata, verify the full tree block. */
+	if (sector->is_metadata) {
+		/*
+		 * Check if the tree block crosses the stripe boudary.  If
+		 * crossed the boundary, we cannot verify it but only give a
+		 * warning.
+		 *
+		 * This can only happen on a very old filesystem where chunks
+		 * are not ensured to be stripe aligned.
+		 */
+		if (unlikely(sector_nr + sectors_per_tree > stripe->nr_sectors)) {
+			btrfs_warn_rl(fs_info,
+			"tree block at %llu crosses stripe boundary %llu",
+				      stripe->logical +
+				      (sector_nr << fs_info->sectorsize_bits),
+				      stripe->logical);
+			return;
+		}
+		scrub_verify_one_metadata(stripe, sector_nr);
+		return;
+	}
+
+	/*
+	 * Data is easier, we just verify the data csum (if we have it).  For
+	 * cases without csum, we have no other choice but to trust it.
+	 */
+	if (!sector->csum) {
+		clear_bit(sector_nr, &stripe->error_bitmap);
+		return;
+	}
+
+	ret = btrfs_check_sector_csum(fs_info, page, pgoff, csum_buf, sector->csum);
+	if (ret < 0) {
+		set_bit(sector_nr, &stripe->csum_error_bitmap);
+		set_bit(sector_nr, &stripe->error_bitmap);
+	} else {
+		clear_bit(sector_nr, &stripe->csum_error_bitmap);
+		clear_bit(sector_nr, &stripe->error_bitmap);
+	}
+}
+
+/* Verify specified sectors of a stripe. */
+static void scrub_verify_one_stripe(struct scrub_stripe *stripe, unsigned long bitmap)
+{
+	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
+	const u32 sectors_per_tree = fs_info->nodesize >> fs_info->sectorsize_bits;
+	int sector_nr;
+
+	for_each_set_bit(sector_nr, &bitmap, stripe->nr_sectors) {
+		scrub_verify_one_sector(stripe, sector_nr);
+		if (stripe->sectors[sector_nr].is_metadata)
+			sector_nr += sectors_per_tree - 1;
+	}
+}
+
+static int calc_sector_number(struct scrub_stripe *stripe, struct bio_vec *first_bvec)
+{
+	int i;
+
+	for (i = 0; i < stripe->nr_sectors; i++) {
+		if (scrub_stripe_get_page(stripe, i) == first_bvec->bv_page &&
+		    scrub_stripe_get_page_offset(stripe, i) == first_bvec->bv_offset)
+			break;
+	}
+	ASSERT(i < stripe->nr_sectors);
+	return i;
+}
+
+/*
+ * Repair read is different to the regular read:
+ *
+ * - Only reads the failed sectors
+ * - May have extra blocksize limits
+ */
+static void scrub_repair_read_endio(struct btrfs_bio *bbio)
+{
+	struct scrub_stripe *stripe = bbio->private;
+	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
+	struct bio_vec *bvec;
+	int sector_nr = calc_sector_number(stripe, bio_first_bvec_all(&bbio->bio));
+	u32 bio_size = 0;
+	int i;
+
+	ASSERT(sector_nr < stripe->nr_sectors);
+
+	bio_for_each_bvec_all(bvec, &bbio->bio, i)
+		bio_size += bvec->bv_len;
+
+	if (bbio->bio.bi_status) {
+		bitmap_set(&stripe->io_error_bitmap, sector_nr,
+			   bio_size >> fs_info->sectorsize_bits);
+		bitmap_set(&stripe->error_bitmap, sector_nr,
+			   bio_size >> fs_info->sectorsize_bits);
+	} else {
+		bitmap_clear(&stripe->io_error_bitmap, sector_nr,
+			     bio_size >> fs_info->sectorsize_bits);
+	}
+	bio_put(&bbio->bio);
+	if (atomic_dec_and_test(&stripe->pending_io))
+		wake_up(&stripe->io_wait);
+}
+
+static int calc_next_mirror(int mirror, int num_copies)
+{
+	ASSERT(mirror <= num_copies);
+	return (mirror + 1 > num_copies) ? 1 : mirror + 1;
+}
+
+static void scrub_stripe_submit_repair_read(struct scrub_stripe *stripe,
+					    int mirror, int blocksize, bool wait)
+{
+	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
+	struct btrfs_bio *bbio = NULL;
+	const unsigned long old_error_bitmap = stripe->error_bitmap;
+	int i;
+
+	ASSERT(stripe->mirror_num >= 1);
+	ASSERT(atomic_read(&stripe->pending_io) == 0);
+
+	for_each_set_bit(i, &old_error_bitmap, stripe->nr_sectors) {
+		struct page *page;
+		int pgoff;
+		int ret;
+
+		page = scrub_stripe_get_page(stripe, i);
+		pgoff = scrub_stripe_get_page_offset(stripe, i);
+
+		/* The current sector cannot be merged, submit the bio. */
+		if (bbio && ((i > 0 && !test_bit(i - 1, &stripe->error_bitmap)) ||
+			     bbio->bio.bi_iter.bi_size >= blocksize)) {
+			ASSERT(bbio->bio.bi_iter.bi_size);
+			atomic_inc(&stripe->pending_io);
+			btrfs_submit_bio(bbio, mirror);
+			if (wait)
+				wait_scrub_stripe_io(stripe);
+			bbio = NULL;
+		}
+
+		if (!bbio) {
+			bbio = btrfs_bio_alloc(stripe->nr_sectors, REQ_OP_READ,
+				fs_info, scrub_repair_read_endio, stripe);
+			bbio->bio.bi_iter.bi_sector = (stripe->logical +
+				(i << fs_info->sectorsize_bits)) >> SECTOR_SHIFT;
+		}
+
+		ret = bio_add_page(&bbio->bio, page, fs_info->sectorsize, pgoff);
+		ASSERT(ret == fs_info->sectorsize);
+	}
+	if (bbio) {
+		ASSERT(bbio->bio.bi_iter.bi_size);
+		atomic_inc(&stripe->pending_io);
+		btrfs_submit_bio(bbio, mirror);
+		if (wait)
+			wait_scrub_stripe_io(stripe);
+	}
+}
+
+static void scrub_stripe_report_errors(struct scrub_ctx *sctx,
+				       struct scrub_stripe *stripe)
+{
+	static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL,
+				      DEFAULT_RATELIMIT_BURST);
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	struct btrfs_device *dev = NULL;
+	u64 physical = 0;
+	int nr_data_sectors = 0;
+	int nr_meta_sectors = 0;
+	int nr_nodatacsum_sectors = 0;
+	int nr_repaired_sectors = 0;
+	int sector_nr;
+
+	if (test_bit(SCRUB_STRIPE_FLAG_NO_REPORT, &stripe->state))
+		return;
+
+	/*
+	 * Init needed infos for error reporting.
+	 *
+	 * Although our scrub_stripe infrastucture is mostly based on btrfs_submit_bio()
+	 * thus no need for dev/physical, error reporting still needs dev and physical.
+	 */
+	if (!bitmap_empty(&stripe->init_error_bitmap, stripe->nr_sectors)) {
+		u64 mapped_len = fs_info->sectorsize;
+		struct btrfs_io_context *bioc = NULL;
+		int stripe_index = stripe->mirror_num - 1;
+		int ret;
+
+		/* For scrub, our mirror_num should always start at 1. */
+		ASSERT(stripe->mirror_num >= 1);
+		ret = btrfs_map_block(fs_info, BTRFS_MAP_GET_READ_MIRRORS,
+				      stripe->logical, &mapped_len, &bioc,
+				      NULL, NULL, 1);
+		/*
+		 * If we failed, dev will be NULL, and later detailed reports
+		 * will just be skipped.
+		 */
+		if (ret < 0)
+			goto skip;
+		physical = bioc->stripes[stripe_index].physical;
+		dev = bioc->stripes[stripe_index].dev;
+		btrfs_put_bioc(bioc);
+	}
+
+skip:
+	for_each_set_bit(sector_nr, &stripe->extent_sector_bitmap, stripe->nr_sectors) {
+		bool repaired = false;
+
+		if (stripe->sectors[sector_nr].is_metadata) {
+			nr_meta_sectors++;
+		} else {
+			nr_data_sectors++;
+			if (!stripe->sectors[sector_nr].csum)
+				nr_nodatacsum_sectors++;
+		}
+
+		if (test_bit(sector_nr, &stripe->init_error_bitmap) &&
+		    !test_bit(sector_nr, &stripe->error_bitmap)) {
+			nr_repaired_sectors++;
+			repaired = true;
+		}
+
+		/* Good sector from the beginning, nothing need to be done. */
+		if (!test_bit(sector_nr, &stripe->init_error_bitmap))
+			continue;
+
+		/*
+		 * Report error for the corrupted sectors.  If repaired, just
+		 * output the message of repaired message.
+		 */
+		if (repaired) {
+			if (dev) {
+				btrfs_err_rl_in_rcu(fs_info,
+			"fixed up error at logical %llu on dev %s physical %llu",
+					    stripe->logical, btrfs_dev_name(dev),
+					    physical);
+			} else {
+				btrfs_err_rl_in_rcu(fs_info,
+			"fixed up error at logical %llu on mirror %u",
+					    stripe->logical, stripe->mirror_num);
+			}
+			continue;
+		}
+
+		/* The remaining are all for unrepaired. */
+		if (dev) {
+			btrfs_err_rl_in_rcu(fs_info,
+	"unable to fixup (regular) error at logical %llu on dev %s physical %llu",
+					    stripe->logical, btrfs_dev_name(dev),
+					    physical);
+		} else {
+			btrfs_err_rl_in_rcu(fs_info,
+	"unable to fixup (regular) error at logical %llu on mirror %u",
+					    stripe->logical, stripe->mirror_num);
+		}
+
+		if (test_bit(sector_nr, &stripe->io_error_bitmap))
+			if (__ratelimit(&rs) && dev)
+				scrub_print_common_warning("i/o error", dev, false,
+						     stripe->logical, physical);
+		if (test_bit(sector_nr, &stripe->csum_error_bitmap))
+			if (__ratelimit(&rs) && dev)
+				scrub_print_common_warning("checksum error", dev, false,
+						     stripe->logical, physical);
+		if (test_bit(sector_nr, &stripe->meta_error_bitmap))
+			if (__ratelimit(&rs) && dev)
+				scrub_print_common_warning("header error", dev, false,
+						     stripe->logical, physical);
+	}
+
+	spin_lock(&sctx->stat_lock);
+	sctx->stat.data_extents_scrubbed += stripe->nr_data_extents;
+	sctx->stat.tree_extents_scrubbed += stripe->nr_meta_extents;
+	sctx->stat.data_bytes_scrubbed += nr_data_sectors << fs_info->sectorsize_bits;
+	sctx->stat.tree_bytes_scrubbed += nr_meta_sectors << fs_info->sectorsize_bits;
+	sctx->stat.no_csum += nr_nodatacsum_sectors;
+	sctx->stat.read_errors += stripe->init_nr_io_errors;
+	sctx->stat.csum_errors += stripe->init_nr_csum_errors;
+	sctx->stat.verify_errors += stripe->init_nr_meta_errors;
+	sctx->stat.uncorrectable_errors +=
+		bitmap_weight(&stripe->error_bitmap, stripe->nr_sectors);
+	sctx->stat.corrected_errors += nr_repaired_sectors;
+	spin_unlock(&sctx->stat_lock);
+}
+
+static void scrub_write_sectors(struct scrub_ctx *sctx, struct scrub_stripe *stripe,
+				unsigned long write_bitmap, bool dev_replace);
+
+/*
+ * The main entrance for all read related scrub work, including:
+ *
+ * - Wait for the initial read to finish
+ * - Verify and locate any bad sectors
+ * - Go through the remaining mirrors and try to read as large blocksize as
+ *   possible
+ * - Go through all mirrors (including the failed mirror) sector-by-sector
+ * - Submit writeback for repaired sectors
+ *
+ * Writeback for dev-replace does not happen here, it needs extra
+ * synchronization for zoned devices.
+ */
+static void scrub_stripe_read_repair_worker(struct work_struct *work)
+{
+	struct scrub_stripe *stripe = container_of(work, struct scrub_stripe, work);
+	struct scrub_ctx *sctx = stripe->sctx;
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	int num_copies = btrfs_num_copies(fs_info, stripe->bg->start,
+					  stripe->bg->length);
+	int mirror;
+	int i;
+
+	ASSERT(stripe->mirror_num > 0);
+
+	wait_scrub_stripe_io(stripe);
+	scrub_verify_one_stripe(stripe, stripe->extent_sector_bitmap);
+	/* Save the initial failed bitmap for later repair and report usage. */
+	stripe->init_error_bitmap = stripe->error_bitmap;
+	stripe->init_nr_io_errors = bitmap_weight(&stripe->io_error_bitmap,
+						  stripe->nr_sectors);
+	stripe->init_nr_csum_errors = bitmap_weight(&stripe->csum_error_bitmap,
+						    stripe->nr_sectors);
+	stripe->init_nr_meta_errors = bitmap_weight(&stripe->meta_error_bitmap,
+						    stripe->nr_sectors);
+
+	if (bitmap_empty(&stripe->init_error_bitmap, stripe->nr_sectors))
+		goto out;
+
+	/*
+	 * Try all remaining mirrors.
+	 *
+	 * Here we still try to read as large block as possible, as this is
+	 * faster and we have extra safety nets to rely on.
+	 */
+	for (mirror = calc_next_mirror(stripe->mirror_num, num_copies);
+	     mirror != stripe->mirror_num;
+	     mirror = calc_next_mirror(mirror, num_copies)) {
+		const unsigned long old_error_bitmap = stripe->error_bitmap;
+
+		scrub_stripe_submit_repair_read(stripe, mirror,
+						BTRFS_STRIPE_LEN, false);
+		wait_scrub_stripe_io(stripe);
+		scrub_verify_one_stripe(stripe, old_error_bitmap);
+		if (bitmap_empty(&stripe->error_bitmap, stripe->nr_sectors))
+			goto out;
+	}
+
+	/*
+	 * Last safety net, try re-checking all mirrors, including the failed
+	 * one, sector-by-sector.
+	 *
+	 * As if one sector failed the drive's internal csum, the whole read
+	 * containing the offending sector would be marked as error.
+	 * Thus here we do sector-by-sector read.
+	 *
+	 * This can be slow, thus we only try it as the last resort.
+	 */
+
+	for (i = 0, mirror = stripe->mirror_num;
+	     i < num_copies;
+	     i++, mirror = calc_next_mirror(mirror, num_copies)) {
+		const unsigned long old_error_bitmap = stripe->error_bitmap;
+
+		scrub_stripe_submit_repair_read(stripe, mirror,
+						fs_info->sectorsize, true);
+		wait_scrub_stripe_io(stripe);
+		scrub_verify_one_stripe(stripe, old_error_bitmap);
+		if (bitmap_empty(&stripe->error_bitmap, stripe->nr_sectors))
+			goto out;
+	}
+out:
+	/*
+	 * Submit the repaired sectors.  For zoned case, we cannot do repair
+	 * in-place, but queue the bg to be relocated.
+	 */
+	if (btrfs_is_zoned(fs_info)) {
+		if (!bitmap_empty(&stripe->error_bitmap, stripe->nr_sectors))
+			btrfs_repair_one_zone(fs_info, sctx->stripes[0].bg->start);
+	} else if (!sctx->readonly) {
+		unsigned long repaired;
+
+		bitmap_andnot(&repaired, &stripe->init_error_bitmap,
+			      &stripe->error_bitmap, stripe->nr_sectors);
+		scrub_write_sectors(sctx, stripe, repaired, false);
+		wait_scrub_stripe_io(stripe);
+	}
+
+	scrub_stripe_report_errors(sctx, stripe);
+	set_bit(SCRUB_STRIPE_FLAG_REPAIR_DONE, &stripe->state);
+	wake_up(&stripe->repair_wait);
+}
+
+static void scrub_read_endio(struct btrfs_bio *bbio)
+{
+	struct scrub_stripe *stripe = bbio->private;
+	struct bio_vec *bvec;
+	int sector_nr = calc_sector_number(stripe, bio_first_bvec_all(&bbio->bio));
+	int num_sectors;
+	u32 bio_size = 0;
+	int i;
+
+	ASSERT(sector_nr < stripe->nr_sectors);
+	bio_for_each_bvec_all(bvec, &bbio->bio, i)
+		bio_size += bvec->bv_len;
+	num_sectors = bio_size >> stripe->bg->fs_info->sectorsize_bits;
+
+	if (bbio->bio.bi_status) {
+		bitmap_set(&stripe->io_error_bitmap, sector_nr, num_sectors);
+		bitmap_set(&stripe->error_bitmap, sector_nr, num_sectors);
+	} else {
+		bitmap_clear(&stripe->io_error_bitmap, sector_nr, num_sectors);
+	}
+	bio_put(&bbio->bio);
+	if (atomic_dec_and_test(&stripe->pending_io)) {
+		wake_up(&stripe->io_wait);
+		INIT_WORK(&stripe->work, scrub_stripe_read_repair_worker);
+		queue_work(stripe->bg->fs_info->scrub_workers, &stripe->work);
+	}
+}
+
+static void scrub_write_endio(struct btrfs_bio *bbio)
+{
+	struct scrub_stripe *stripe = bbio->private;
+	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
+	struct bio_vec *bvec;
+	int sector_nr = calc_sector_number(stripe, bio_first_bvec_all(&bbio->bio));
+	u32 bio_size = 0;
+	int i;
+
+	bio_for_each_bvec_all(bvec, &bbio->bio, i)
+		bio_size += bvec->bv_len;
+
+	if (bbio->bio.bi_status) {
+		unsigned long flags;
+
+		spin_lock_irqsave(&stripe->write_error_lock, flags);
+		bitmap_set(&stripe->write_error_bitmap, sector_nr,
+			   bio_size >> fs_info->sectorsize_bits);
+		spin_unlock_irqrestore(&stripe->write_error_lock, flags);
+	}
+	bio_put(&bbio->bio);
+
+	if (atomic_dec_and_test(&stripe->pending_io))
+		wake_up(&stripe->io_wait);
+}
+
+static void scrub_submit_write_bio(struct scrub_ctx *sctx,
+				   struct scrub_stripe *stripe,
+				   struct btrfs_bio *bbio, bool dev_replace)
+{
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	u32 bio_len = bbio->bio.bi_iter.bi_size;
+	u32 bio_off = (bbio->bio.bi_iter.bi_sector << SECTOR_SHIFT) -
+		      stripe->logical;
+
+	fill_writer_pointer_gap(sctx, stripe->physical + bio_off);
+	atomic_inc(&stripe->pending_io);
+	btrfs_submit_repair_write(bbio, stripe->mirror_num, dev_replace);
+	if (!btrfs_is_zoned(fs_info))
+		return;
+	/*
+	 * For zoned writeback, queue depth must be 1, thus we must wait for
+	 * the write to finish before the next write.
+	 */
+	wait_scrub_stripe_io(stripe);
+
+	/*
+	 * And also need to update the write pointer if write finished
+	 * successfully.
+	 */
+	if (!test_bit(bio_off >> fs_info->sectorsize_bits,
+		      &stripe->write_error_bitmap))
+		sctx->write_pointer += bio_len;
+}
+
+/*
+ * Submit the write bio(s) for the sectors specified by @write_bitmap.
+ *
+ * Here we utilize btrfs_submit_repair_write(), which has some extra benefits:
+ *
+ * - Only needs logical bytenr and mirror_num
+ *   Just like the scrub read path
+ *
+ * - Would only result in writes to the specified mirror
+ *   Unlike the regular writeback path, which would write back to all stripes
+ *
+ * - Handle dev-replace and read-repair writeback differently
+ */
+static void scrub_write_sectors(struct scrub_ctx *sctx, struct scrub_stripe *stripe,
+				unsigned long write_bitmap, bool dev_replace)
+{
+	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
+	struct btrfs_bio *bbio = NULL;
+	int sector_nr;
+
+	for_each_set_bit(sector_nr, &write_bitmap, stripe->nr_sectors) {
+		struct page *page = scrub_stripe_get_page(stripe, sector_nr);
+		unsigned int pgoff = scrub_stripe_get_page_offset(stripe, sector_nr);
+		int ret;
+
+		/* We should only writeback sectors covered by an extent. */
+		ASSERT(test_bit(sector_nr, &stripe->extent_sector_bitmap));
+
+		/* Cannot merge with previous sector, submit the current one. */
+		if (bbio && sector_nr && !test_bit(sector_nr - 1, &write_bitmap)) {
+			scrub_submit_write_bio(sctx, stripe, bbio, dev_replace);
+			bbio = NULL;
+		}
+		if (!bbio) {
+			bbio = btrfs_bio_alloc(stripe->nr_sectors, REQ_OP_WRITE,
+					       fs_info, scrub_write_endio, stripe);
+			bbio->bio.bi_iter.bi_sector = (stripe->logical +
+				(sector_nr << fs_info->sectorsize_bits)) >>
+				SECTOR_SHIFT;
+		}
+		ret = bio_add_page(&bbio->bio, page, fs_info->sectorsize, pgoff);
+		ASSERT(ret == fs_info->sectorsize);
+	}
+	if (bbio)
+		scrub_submit_write_bio(sctx, stripe, bbio, dev_replace);
+}
+
+/*
+ * 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_dev_io(struct scrub_ctx *sctx, struct btrfs_device *device,
+				  unsigned int bio_size)
+{
+	const int time_slice = 1000;
+	s64 delta;
+	ktime_t now;
+	u32 div;
+	u64 bwlimit;
+
+	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 += bio_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;
+}
+
+/*
+ * 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 last_offset;
+	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++) {
+		u32 stripe_nr;
+		u32 stripe_index;
+		u32 rot;
+
+		*offset = last_offset + btrfs_stripe_nr_to_offset(i);
+
+		stripe_nr = (u32)(*offset >> BTRFS_STRIPE_LEN_SHIFT) / data_stripes;
+
+		/* Work out the disk rotation on this stripe-set */
+		rot = stripe_nr % map->num_stripes;
+		/* 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 + btrfs_stripe_nr_to_offset(j);
+	return 1;
+}
+
+/*
+ * 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 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;
+
+	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;
+}
+
+static void fill_one_extent_info(struct btrfs_fs_info *fs_info,
+				 struct scrub_stripe *stripe,
+				 u64 extent_start, u64 extent_len,
+				 u64 extent_flags, u64 extent_gen)
+{
+	for (u64 cur_logical = max(stripe->logical, extent_start);
+	     cur_logical < min(stripe->logical + BTRFS_STRIPE_LEN,
+			       extent_start + extent_len);
+	     cur_logical += fs_info->sectorsize) {
+		const int nr_sector = (cur_logical - stripe->logical) >>
+				      fs_info->sectorsize_bits;
+		struct scrub_sector_verification *sector =
+						&stripe->sectors[nr_sector];
+
+		set_bit(nr_sector, &stripe->extent_sector_bitmap);
+		if (extent_flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
+			sector->is_metadata = true;
+			sector->generation = extent_gen;
+		}
+	}
+}
+
+static void scrub_stripe_reset_bitmaps(struct scrub_stripe *stripe)
+{
+	stripe->extent_sector_bitmap = 0;
+	stripe->init_error_bitmap = 0;
+	stripe->init_nr_io_errors = 0;
+	stripe->init_nr_csum_errors = 0;
+	stripe->init_nr_meta_errors = 0;
+	stripe->error_bitmap = 0;
+	stripe->io_error_bitmap = 0;
+	stripe->csum_error_bitmap = 0;
+	stripe->meta_error_bitmap = 0;
+}
+
+/*
+ * Locate one stripe which has at least one extent in its range.
+ *
+ * Return 0 if found such stripe, and store its info into @stripe.
+ * Return >0 if there is no such stripe in the specified range.
+ * Return <0 for error.
+ */
+static int scrub_find_fill_first_stripe(struct btrfs_block_group *bg,
+					struct btrfs_path *extent_path,
+					struct btrfs_path *csum_path,
+					struct btrfs_device *dev, u64 physical,
+					int mirror_num, u64 logical_start,
+					u32 logical_len,
+					struct scrub_stripe *stripe)
+{
+	struct btrfs_fs_info *fs_info = bg->fs_info;
+	struct btrfs_root *extent_root = btrfs_extent_root(fs_info, bg->start);
+	struct btrfs_root *csum_root = btrfs_csum_root(fs_info, bg->start);
+	const u64 logical_end = logical_start + logical_len;
+	u64 cur_logical = logical_start;
+	u64 stripe_end;
+	u64 extent_start;
+	u64 extent_len;
+	u64 extent_flags;
+	u64 extent_gen;
+	int ret;
+
+	memset(stripe->sectors, 0, sizeof(struct scrub_sector_verification) *
+				   stripe->nr_sectors);
+	scrub_stripe_reset_bitmaps(stripe);
+
+	/* The range must be inside the bg. */
+	ASSERT(logical_start >= bg->start && logical_end <= bg->start + bg->length);
+
+	ret = find_first_extent_item(extent_root, extent_path, logical_start,
+				     logical_len);
+	/* Either error or not found. */
+	if (ret)
+		goto out;
+	get_extent_info(extent_path, &extent_start, &extent_len, &extent_flags,
+			&extent_gen);
+	if (extent_flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)
+		stripe->nr_meta_extents++;
+	if (extent_flags & BTRFS_EXTENT_FLAG_DATA)
+		stripe->nr_data_extents++;
+	cur_logical = max(extent_start, cur_logical);
+
+	/*
+	 * Round down to stripe boundary.
+	 *
+	 * The extra calculation against bg->start is to handle block groups
+	 * whose logical bytenr is not BTRFS_STRIPE_LEN aligned.
+	 */
+	stripe->logical = round_down(cur_logical - bg->start, BTRFS_STRIPE_LEN) +
+			  bg->start;
+	stripe->physical = physical + stripe->logical - logical_start;
+	stripe->dev = dev;
+	stripe->bg = bg;
+	stripe->mirror_num = mirror_num;
+	stripe_end = stripe->logical + BTRFS_STRIPE_LEN - 1;
+
+	/* Fill the first extent info into stripe->sectors[] array. */
+	fill_one_extent_info(fs_info, stripe, extent_start, extent_len,
+			     extent_flags, extent_gen);
+	cur_logical = extent_start + extent_len;
+
+	/* Fill the extent info for the remaining sectors. */
+	while (cur_logical <= stripe_end) {
+		ret = find_first_extent_item(extent_root, extent_path, cur_logical,
+					     stripe_end - cur_logical + 1);
+		if (ret < 0)
+			goto out;
+		if (ret > 0) {
+			ret = 0;
+			break;
+		}
+		get_extent_info(extent_path, &extent_start, &extent_len,
+				&extent_flags, &extent_gen);
+		if (extent_flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)
+			stripe->nr_meta_extents++;
+		if (extent_flags & BTRFS_EXTENT_FLAG_DATA)
+			stripe->nr_data_extents++;
+		fill_one_extent_info(fs_info, stripe, extent_start, extent_len,
+				     extent_flags, extent_gen);
+		cur_logical = extent_start + extent_len;
+	}
+
+	/* Now fill the data csum. */
+	if (bg->flags & BTRFS_BLOCK_GROUP_DATA) {
+		int sector_nr;
+		unsigned long csum_bitmap = 0;
+
+		/* Csum space should have already been allocated. */
+		ASSERT(stripe->csums);
+
+		/*
+		 * Our csum bitmap should be large enough, as BTRFS_STRIPE_LEN
+		 * should contain at most 16 sectors.
+		 */
+		ASSERT(BITS_PER_LONG >= BTRFS_STRIPE_LEN >> fs_info->sectorsize_bits);
+
+		ret = btrfs_lookup_csums_bitmap(csum_root, csum_path,
+						stripe->logical, stripe_end,
+						stripe->csums, &csum_bitmap);
+		if (ret < 0)
+			goto out;
+		if (ret > 0)
+			ret = 0;
+
+		for_each_set_bit(sector_nr, &csum_bitmap, stripe->nr_sectors) {
+			stripe->sectors[sector_nr].csum = stripe->csums +
+				sector_nr * fs_info->csum_size;
+		}
+	}
+	set_bit(SCRUB_STRIPE_FLAG_INITIALIZED, &stripe->state);
+out:
+	return ret;
+}
+
+static void scrub_reset_stripe(struct scrub_stripe *stripe)
+{
+	scrub_stripe_reset_bitmaps(stripe);
+
+	stripe->nr_meta_extents = 0;
+	stripe->nr_data_extents = 0;
+	stripe->state = 0;
+
+	for (int i = 0; i < stripe->nr_sectors; i++) {
+		stripe->sectors[i].is_metadata = false;
+		stripe->sectors[i].csum = NULL;
+		stripe->sectors[i].generation = 0;
+	}
+}
+
+static void scrub_submit_initial_read(struct scrub_ctx *sctx,
+				      struct scrub_stripe *stripe)
+{
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	struct btrfs_bio *bbio;
+	unsigned int nr_sectors = min_t(u64, BTRFS_STRIPE_LEN, stripe->bg->start +
+				      stripe->bg->length - stripe->logical) >>
+				  fs_info->sectorsize_bits;
+	int mirror = stripe->mirror_num;
+
+	ASSERT(stripe->bg);
+	ASSERT(stripe->mirror_num > 0);
+	ASSERT(test_bit(SCRUB_STRIPE_FLAG_INITIALIZED, &stripe->state));
+
+	bbio = btrfs_bio_alloc(SCRUB_STRIPE_PAGES, REQ_OP_READ, fs_info,
+			       scrub_read_endio, stripe);
+
+	bbio->bio.bi_iter.bi_sector = stripe->logical >> SECTOR_SHIFT;
+	/* Read the whole range inside the chunk boundary. */
+	for (unsigned int cur = 0; cur < nr_sectors; cur++) {
+		struct page *page = scrub_stripe_get_page(stripe, cur);
+		unsigned int pgoff = scrub_stripe_get_page_offset(stripe, cur);
+		int ret;
+
+		ret = bio_add_page(&bbio->bio, page, fs_info->sectorsize, pgoff);
+		/* We should have allocated enough bio vectors. */
+		ASSERT(ret == fs_info->sectorsize);
+	}
+	atomic_inc(&stripe->pending_io);
+
+	/*
+	 * For dev-replace, either user asks to avoid the source dev, or
+	 * the device is missing, we try the next mirror instead.
+	 */
+	if (sctx->is_dev_replace &&
+	    (fs_info->dev_replace.cont_reading_from_srcdev_mode ==
+	     BTRFS_DEV_REPLACE_ITEM_CONT_READING_FROM_SRCDEV_MODE_AVOID ||
+	     !stripe->dev->bdev)) {
+		int num_copies = btrfs_num_copies(fs_info, stripe->bg->start,
+						  stripe->bg->length);
+
+		mirror = calc_next_mirror(mirror, num_copies);
+	}
+	btrfs_submit_bio(bbio, mirror);
+}
+
+static bool stripe_has_metadata_error(struct scrub_stripe *stripe)
+{
+	int i;
+
+	for_each_set_bit(i, &stripe->error_bitmap, stripe->nr_sectors) {
+		if (stripe->sectors[i].is_metadata) {
+			struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
+
+			btrfs_err(fs_info,
+			"stripe %llu has unrepaired metadata sector at %llu",
+				  stripe->logical,
+				  stripe->logical + (i << fs_info->sectorsize_bits));
+			return true;
+		}
+	}
+	return false;
+}
+
+static void submit_initial_group_read(struct scrub_ctx *sctx,
+				      unsigned int first_slot,
+				      unsigned int nr_stripes)
+{
+	struct blk_plug plug;
+
+	ASSERT(first_slot < SCRUB_TOTAL_STRIPES);
+	ASSERT(first_slot + nr_stripes <= SCRUB_TOTAL_STRIPES);
+
+	scrub_throttle_dev_io(sctx, sctx->stripes[0].dev,
+			      btrfs_stripe_nr_to_offset(nr_stripes));
+	blk_start_plug(&plug);
+	for (int i = 0; i < nr_stripes; i++) {
+		struct scrub_stripe *stripe = &sctx->stripes[first_slot + i];
+
+		/* Those stripes should be initialized. */
+		ASSERT(test_bit(SCRUB_STRIPE_FLAG_INITIALIZED, &stripe->state));
+		scrub_submit_initial_read(sctx, stripe);
+	}
+	blk_finish_plug(&plug);
+}
+
+static int flush_scrub_stripes(struct scrub_ctx *sctx)
+{
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	struct scrub_stripe *stripe;
+	const int nr_stripes = sctx->cur_stripe;
+	int ret = 0;
+
+	if (!nr_stripes)
+		return 0;
+
+	ASSERT(test_bit(SCRUB_STRIPE_FLAG_INITIALIZED, &sctx->stripes[0].state));
+
+	/* Submit the stripes which are populated but not submitted. */
+	if (nr_stripes % SCRUB_STRIPES_PER_GROUP) {
+		const int first_slot = round_down(nr_stripes, SCRUB_STRIPES_PER_GROUP);
+
+		submit_initial_group_read(sctx, first_slot, nr_stripes - first_slot);
+	}
+
+	for (int i = 0; i < nr_stripes; i++) {
+		stripe = &sctx->stripes[i];
+
+		wait_event(stripe->repair_wait,
+			   test_bit(SCRUB_STRIPE_FLAG_REPAIR_DONE, &stripe->state));
+	}
+
+	/* Submit for dev-replace. */
+	if (sctx->is_dev_replace) {
+		/*
+		 * For dev-replace, if we know there is something wrong with
+		 * metadata, we should immedately abort.
+		 */
+		for (int i = 0; i < nr_stripes; i++) {
+			if (stripe_has_metadata_error(&sctx->stripes[i])) {
+				ret = -EIO;
+				goto out;
+			}
+		}
+		for (int i = 0; i < nr_stripes; i++) {
+			unsigned long good;
+
+			stripe = &sctx->stripes[i];
+
+			ASSERT(stripe->dev == fs_info->dev_replace.srcdev);
+
+			bitmap_andnot(&good, &stripe->extent_sector_bitmap,
+				      &stripe->error_bitmap, stripe->nr_sectors);
+			scrub_write_sectors(sctx, stripe, good, true);
+		}
+	}
+
+	/* Wait for the above writebacks to finish. */
+	for (int i = 0; i < nr_stripes; i++) {
+		stripe = &sctx->stripes[i];
+
+		wait_scrub_stripe_io(stripe);
+		scrub_reset_stripe(stripe);
+	}
+out:
+	sctx->cur_stripe = 0;
+	return ret;
+}
+
+static void raid56_scrub_wait_endio(struct bio *bio)
+{
+	complete(bio->bi_private);
+}
+
+static int queue_scrub_stripe(struct scrub_ctx *sctx, struct btrfs_block_group *bg,
+			      struct btrfs_device *dev, int mirror_num,
+			      u64 logical, u32 length, u64 physical,
+			      u64 *found_logical_ret)
+{
+	struct scrub_stripe *stripe;
+	int ret;
+
+	/*
+	 * There should always be one slot left, as caller filling the last
+	 * slot should flush them all.
+	 */
+	ASSERT(sctx->cur_stripe < SCRUB_TOTAL_STRIPES);
+
+	/* @found_logical_ret must be specified. */
+	ASSERT(found_logical_ret);
+
+	stripe = &sctx->stripes[sctx->cur_stripe];
+	scrub_reset_stripe(stripe);
+	ret = scrub_find_fill_first_stripe(bg, &sctx->extent_path,
+					   &sctx->csum_path, dev, physical,
+					   mirror_num, logical, length, stripe);
+	/* Either >0 as no more extents or <0 for error. */
+	if (ret)
+		return ret;
+	*found_logical_ret = stripe->logical;
+	sctx->cur_stripe++;
+
+	/* We filled one group, submit it. */
+	if (sctx->cur_stripe % SCRUB_STRIPES_PER_GROUP == 0) {
+		const int first_slot = sctx->cur_stripe - SCRUB_STRIPES_PER_GROUP;
+
+		submit_initial_group_read(sctx, first_slot, SCRUB_STRIPES_PER_GROUP);
+	}
+
+	/* Last slot used, flush them all. */
+	if (sctx->cur_stripe == SCRUB_TOTAL_STRIPES)
+		return flush_scrub_stripes(sctx);
+	return 0;
+}
+
+static int scrub_raid56_parity_stripe(struct scrub_ctx *sctx,
+				      struct btrfs_device *scrub_dev,
+				      struct btrfs_block_group *bg,
+				      struct map_lookup *map,
+				      u64 full_stripe_start)
+{
+	DECLARE_COMPLETION_ONSTACK(io_done);
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	struct btrfs_raid_bio *rbio;
+	struct btrfs_io_context *bioc = NULL;
+	struct btrfs_path extent_path = { 0 };
+	struct btrfs_path csum_path = { 0 };
+	struct bio *bio;
+	struct scrub_stripe *stripe;
+	bool all_empty = true;
+	const int data_stripes = nr_data_stripes(map);
+	unsigned long extent_bitmap = 0;
+	u64 length = btrfs_stripe_nr_to_offset(data_stripes);
+	int ret;
+
+	ASSERT(sctx->raid56_data_stripes);
+
+	/*
+	 * For data stripe search, we cannot re-use the same extent/csum paths,
+	 * as the data stripe bytenr may be smaller than previous extent.  Thus
+	 * we have to use our own extent/csum paths.
+	 */
+	extent_path.search_commit_root = 1;
+	extent_path.skip_locking = 1;
+	csum_path.search_commit_root = 1;
+	csum_path.skip_locking = 1;
+
+	for (int i = 0; i < data_stripes; i++) {
+		int stripe_index;
+		int rot;
+		u64 physical;
+
+		stripe = &sctx->raid56_data_stripes[i];
+		rot = div_u64(full_stripe_start - bg->start,
+			      data_stripes) >> BTRFS_STRIPE_LEN_SHIFT;
+		stripe_index = (i + rot) % map->num_stripes;
+		physical = map->stripes[stripe_index].physical +
+			   btrfs_stripe_nr_to_offset(rot);
+
+		scrub_reset_stripe(stripe);
+		set_bit(SCRUB_STRIPE_FLAG_NO_REPORT, &stripe->state);
+		ret = scrub_find_fill_first_stripe(bg, &extent_path, &csum_path,
+				map->stripes[stripe_index].dev, physical, 1,
+				full_stripe_start + btrfs_stripe_nr_to_offset(i),
+				BTRFS_STRIPE_LEN, stripe);
+		if (ret < 0)
+			goto out;
+		/*
+		 * No extent in this data stripe, need to manually mark them
+		 * initialized to make later read submission happy.
+		 */
+		if (ret > 0) {
+			stripe->logical = full_stripe_start +
+					  btrfs_stripe_nr_to_offset(i);
+			stripe->dev = map->stripes[stripe_index].dev;
+			stripe->mirror_num = 1;
+			set_bit(SCRUB_STRIPE_FLAG_INITIALIZED, &stripe->state);
+		}
+	}
+
+	/* Check if all data stripes are empty. */
+	for (int i = 0; i < data_stripes; i++) {
+		stripe = &sctx->raid56_data_stripes[i];
+		if (!bitmap_empty(&stripe->extent_sector_bitmap, stripe->nr_sectors)) {
+			all_empty = false;
+			break;
+		}
+	}
+	if (all_empty) {
+		ret = 0;
+		goto out;
+	}
+
+	for (int i = 0; i < data_stripes; i++) {
+		stripe = &sctx->raid56_data_stripes[i];
+		scrub_submit_initial_read(sctx, stripe);
+	}
+	for (int i = 0; i < data_stripes; i++) {
+		stripe = &sctx->raid56_data_stripes[i];
+
+		wait_event(stripe->repair_wait,
+			   test_bit(SCRUB_STRIPE_FLAG_REPAIR_DONE, &stripe->state));
+	}
+	/* For now, no zoned support for RAID56. */
+	ASSERT(!btrfs_is_zoned(sctx->fs_info));
+
+	/*
+	 * Now all data stripes are properly verified. Check if we have any
+	 * unrepaired, if so abort immediately or we could further corrupt the
+	 * P/Q stripes.
+	 *
+	 * During the loop, also populate extent_bitmap.
+	 */
+	for (int i = 0; i < data_stripes; i++) {
+		unsigned long error;
+
+		stripe = &sctx->raid56_data_stripes[i];
+
+		/*
+		 * We should only check the errors where there is an extent.
+		 * As we may hit an empty data stripe while it's missing.
+		 */
+		bitmap_and(&error, &stripe->error_bitmap,
+			   &stripe->extent_sector_bitmap, stripe->nr_sectors);
+		if (!bitmap_empty(&error, stripe->nr_sectors)) {
+			btrfs_err(fs_info,
+"unrepaired sectors detected, full stripe %llu data stripe %u errors %*pbl",
+				  full_stripe_start, i, stripe->nr_sectors,
+				  &error);
+			ret = -EIO;
+			goto out;
+		}
+		bitmap_or(&extent_bitmap, &extent_bitmap,
+			  &stripe->extent_sector_bitmap, stripe->nr_sectors);
+	}
+
+	/* Now we can check and regenerate the P/Q stripe. */
+	bio = bio_alloc(NULL, 1, REQ_OP_READ, GFP_NOFS);
+	bio->bi_iter.bi_sector = full_stripe_start >> SECTOR_SHIFT;
+	bio->bi_private = &io_done;
+	bio->bi_end_io = raid56_scrub_wait_endio;
+
+	btrfs_bio_counter_inc_blocked(fs_info);
+	ret = btrfs_map_block(fs_info, BTRFS_MAP_WRITE, full_stripe_start,
+			      &length, &bioc, NULL, NULL, 1);
+	if (ret < 0) {
+		btrfs_put_bioc(bioc);
+		btrfs_bio_counter_dec(fs_info);
+		goto out;
+	}
+	rbio = raid56_parity_alloc_scrub_rbio(bio, bioc, scrub_dev, &extent_bitmap,
+				BTRFS_STRIPE_LEN >> fs_info->sectorsize_bits);
+	btrfs_put_bioc(bioc);
+	if (!rbio) {
+		ret = -ENOMEM;
+		btrfs_bio_counter_dec(fs_info);
+		goto out;
+	}
+	/* Use the recovered stripes as cache to avoid read them from disk again. */
+	for (int i = 0; i < data_stripes; i++) {
+		stripe = &sctx->raid56_data_stripes[i];
+
+		raid56_parity_cache_data_pages(rbio, stripe->pages,
+				full_stripe_start + (i << BTRFS_STRIPE_LEN_SHIFT));
+	}
+	raid56_parity_submit_scrub_rbio(rbio);
+	wait_for_completion_io(&io_done);
+	ret = blk_status_to_errno(bio->bi_status);
+	bio_put(bio);
+	btrfs_bio_counter_dec(fs_info);
+
+	btrfs_release_path(&extent_path);
+	btrfs_release_path(&csum_path);
+out:
+	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_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;
+	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);
+
+	/* Go through each extent items inside the logical range */
+	while (cur_logical < logical_end) {
+		u64 found_logical = U64_MAX;
+		u64 cur_physical = physical + cur_logical - logical_start;
+
+		/* 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 */
+			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 = queue_scrub_stripe(sctx, bg, device, mirror_num,
+					 cur_logical, logical_end - cur_logical,
+					 cur_physical, &found_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;
+
+		/* queue_scrub_stripe() returned 0, @found_logical must be updated. */
+		ASSERT(found_logical != U64_MAX);
+		cur_logical = found_logical + BTRFS_STRIPE_LEN;
+
+		/* Don't hold CPU for too long time */
+		cond_resched();
+	}
+	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 btrfs_stripe_nr_to_offset(map->num_stripes / map->sub_stripes);
+}
+
+/* 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 btrfs_stripe_nr_to_offset(stripe_index / map->sub_stripes) +
+	       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_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, bg, map, cur_logical,
+					  BTRFS_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 += BTRFS_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_fs_info *fs_info = sctx->fs_info;
+	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;
+	int ret2;
+	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;
+	int stop_loop = 0;
+
+	/* Extent_path should be released by now. */
+	ASSERT(sctx->extent_path.nodes[0] == NULL);
+
+	scrub_blocked_if_needed(fs_info);
+
+	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);
+	}
+
+	/* Prepare the extra data stripes used by RAID56. */
+	if (profile & BTRFS_BLOCK_GROUP_RAID56_MASK) {
+		ASSERT(sctx->raid56_data_stripes == NULL);
+
+		sctx->raid56_data_stripes = kcalloc(nr_data_stripes(map),
+						    sizeof(struct scrub_stripe),
+						    GFP_KERNEL);
+		if (!sctx->raid56_data_stripes) {
+			ret = -ENOMEM;
+			goto out;
+		}
+		for (int i = 0; i < nr_data_stripes(map); i++) {
+			ret = init_scrub_stripe(fs_info,
+						&sctx->raid56_data_stripes[i]);
+			if (ret < 0)
+				goto out;
+			sctx->raid56_data_stripes[i].bg = bg;
+			sctx->raid56_data_stripes[i].sctx = sctx;
+		}
+	}
+	/*
+	 * 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, 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, bg, map, scrub_dev, stripe_index);
+		offset = btrfs_stripe_nr_to_offset(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 = btrfs_stripe_nr_to_offset(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;
+			ret = scrub_raid56_parity_stripe(sctx, scrub_dev, bg,
+							 map, stripe_logical);
+			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, bg, map, logical, BTRFS_STRIPE_LEN,
+					  scrub_dev, physical, 1);
+		if (ret < 0)
+			goto out;
+next:
+		logical += increment;
+		physical += BTRFS_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:
+	ret2 = flush_scrub_stripes(sctx);
+	if (!ret)
+		ret = ret2;
+	btrfs_release_path(&sctx->extent_path);
+	btrfs_release_path(&sctx->csum_path);
+
+	if (sctx->raid56_data_stripes) {
+		for (int i = 0; i < nr_data_stripes(map); i++)
+			release_scrub_stripe(&sctx->raid56_data_stripes[i]);
+		kfree(sctx->raid56_data_stripes);
+		sctx->raid56_data_stripes = NULL;
+	}
+
+	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);
+		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 int scrub_one_super(struct scrub_ctx *sctx, struct btrfs_device *dev,
+			   struct page *page, u64 physical, u64 generation)
+{
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	struct bio_vec bvec;
+	struct bio bio;
+	struct btrfs_super_block *sb = page_address(page);
+	int ret;
+
+	bio_init(&bio, dev->bdev, &bvec, 1, REQ_OP_READ);
+	bio.bi_iter.bi_sector = physical >> SECTOR_SHIFT;
+	__bio_add_page(&bio, page, BTRFS_SUPER_INFO_SIZE, 0);
+	ret = submit_bio_wait(&bio);
+	bio_uninit(&bio);
+
+	if (ret < 0)
+		return ret;
+	ret = btrfs_check_super_csum(fs_info, sb);
+	if (ret != 0) {
+		btrfs_err_rl(fs_info,
+			"super block at physical %llu devid %llu has bad csum",
+			physical, dev->devid);
+		return -EIO;
+	}
+	if (btrfs_super_generation(sb) != generation) {
+		btrfs_err_rl(fs_info,
+"super block at physical %llu devid %llu has bad generation %llu expect %llu",
+			     physical, dev->devid,
+			     btrfs_super_generation(sb), generation);
+		return -EUCLEAN;
+	}
+
+	return btrfs_validate_super(fs_info, sb, -1);
+}
+
+static noinline_for_stack int scrub_supers(struct scrub_ctx *sctx,
+					   struct btrfs_device *scrub_dev)
+{
+	int	i;
+	u64	bytenr;
+	u64	gen;
+	int ret = 0;
+	struct page *page;
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+
+	if (BTRFS_FS_ERROR(fs_info))
+		return -EROFS;
+
+	page = alloc_page(GFP_KERNEL);
+	if (!page) {
+		spin_lock(&sctx->stat_lock);
+		sctx->stat.malloc_errors++;
+		spin_unlock(&sctx->stat_lock);
+		return -ENOMEM;
+	}
+
+	/* 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_one_super(sctx, scrub_dev, page, bytenr, gen);
+		if (ret) {
+			spin_lock(&sctx->stat_lock);
+			sctx->stat.super_errors++;
+			spin_unlock(&sctx->stat_lock);
+		}
+	}
+	__free_page(page);
+	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;
+
+		fs_info->scrub_workers = NULL;
+		mutex_unlock(&fs_info->scrub_lock);
+
+		if (scrub_workers)
+			destroy_workqueue(scrub_workers);
+	}
+}
+
+/*
+ * 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)
+{
+	struct workqueue_struct *scrub_workers = 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, max_active);
+	if (!scrub_workers)
+		return -ENOMEM;
+
+	mutex_lock(&fs_info->scrub_lock);
+	if (refcount_read(&fs_info->scrub_workers_refcnt) == 0) {
+		ASSERT(fs_info->scrub_workers == NULL);
+		fs_info->scrub_workers = scrub_workers;
+		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_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);
+	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, btrfs_dev_name(dev));
+		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);
+
+	atomic_dec(&fs_info->scrubs_running);
+	wake_up(&fs_info->scrub_pause_wait);
+
+	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;
+}