Adding upstream version 6.1.76.upstream/6.1.76upstream

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

1 files changed, 2761 insertions, 0 deletions

diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
new file mode 100644
index 000000000..82c8e9913
--- /dev/null
+++ b/fs/btrfs/raid56.c
@@ -0,0 +1,2761 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2012 Fusion-io  All rights reserved.
+ * Copyright (C) 2012 Intel Corp. All rights reserved.
+ */
+
+#include <linux/sched.h>
+#include <linux/bio.h>
+#include <linux/slab.h>
+#include <linux/blkdev.h>
+#include <linux/raid/pq.h>
+#include <linux/hash.h>
+#include <linux/list_sort.h>
+#include <linux/raid/xor.h>
+#include <linux/mm.h>
+#include "misc.h"
+#include "ctree.h"
+#include "disk-io.h"
+#include "volumes.h"
+#include "raid56.h"
+#include "async-thread.h"
+
+/* set when additional merges to this rbio are not allowed */
+#define RBIO_RMW_LOCKED_BIT	1
+
+/*
+ * set when this rbio is sitting in the hash, but it is just a cache
+ * of past RMW
+ */
+#define RBIO_CACHE_BIT		2
+
+/*
+ * set when it is safe to trust the stripe_pages for caching
+ */
+#define RBIO_CACHE_READY_BIT	3
+
+#define RBIO_CACHE_SIZE 1024
+
+#define BTRFS_STRIPE_HASH_TABLE_BITS				11
+
+/* Used by the raid56 code to lock stripes for read/modify/write */
+struct btrfs_stripe_hash {
+	struct list_head hash_list;
+	spinlock_t lock;
+};
+
+/* Used by the raid56 code to lock stripes for read/modify/write */
+struct btrfs_stripe_hash_table {
+	struct list_head stripe_cache;
+	spinlock_t cache_lock;
+	int cache_size;
+	struct btrfs_stripe_hash table[];
+};
+
+/*
+ * A bvec like structure to present a sector inside a page.
+ *
+ * Unlike bvec we don't need bvlen, as it's fixed to sectorsize.
+ */
+struct sector_ptr {
+	struct page *page;
+	unsigned int pgoff:24;
+	unsigned int uptodate:8;
+};
+
+static int __raid56_parity_recover(struct btrfs_raid_bio *rbio);
+static noinline void finish_rmw(struct btrfs_raid_bio *rbio);
+static void rmw_work(struct work_struct *work);
+static void read_rebuild_work(struct work_struct *work);
+static int fail_bio_stripe(struct btrfs_raid_bio *rbio, struct bio *bio);
+static int fail_rbio_index(struct btrfs_raid_bio *rbio, int failed);
+static void __free_raid_bio(struct btrfs_raid_bio *rbio);
+static void index_rbio_pages(struct btrfs_raid_bio *rbio);
+static int alloc_rbio_pages(struct btrfs_raid_bio *rbio);
+
+static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
+					 int need_check);
+static void scrub_parity_work(struct work_struct *work);
+
+static void start_async_work(struct btrfs_raid_bio *rbio, work_func_t work_func)
+{
+	INIT_WORK(&rbio->work, work_func);
+	queue_work(rbio->bioc->fs_info->rmw_workers, &rbio->work);
+}
+
+/*
+ * the stripe hash table is used for locking, and to collect
+ * bios in hopes of making a full stripe
+ */
+int btrfs_alloc_stripe_hash_table(struct btrfs_fs_info *info)
+{
+	struct btrfs_stripe_hash_table *table;
+	struct btrfs_stripe_hash_table *x;
+	struct btrfs_stripe_hash *cur;
+	struct btrfs_stripe_hash *h;
+	int num_entries = 1 << BTRFS_STRIPE_HASH_TABLE_BITS;
+	int i;
+
+	if (info->stripe_hash_table)
+		return 0;
+
+	/*
+	 * The table is large, starting with order 4 and can go as high as
+	 * order 7 in case lock debugging is turned on.
+	 *
+	 * Try harder to allocate and fallback to vmalloc to lower the chance
+	 * of a failing mount.
+	 */
+	table = kvzalloc(struct_size(table, table, num_entries), GFP_KERNEL);
+	if (!table)
+		return -ENOMEM;
+
+	spin_lock_init(&table->cache_lock);
+	INIT_LIST_HEAD(&table->stripe_cache);
+
+	h = table->table;
+
+	for (i = 0; i < num_entries; i++) {
+		cur = h + i;
+		INIT_LIST_HEAD(&cur->hash_list);
+		spin_lock_init(&cur->lock);
+	}
+
+	x = cmpxchg(&info->stripe_hash_table, NULL, table);
+	kvfree(x);
+	return 0;
+}
+
+/*
+ * caching an rbio means to copy anything from the
+ * bio_sectors array into the stripe_pages array.  We
+ * use the page uptodate bit in the stripe cache array
+ * to indicate if it has valid data
+ *
+ * once the caching is done, we set the cache ready
+ * bit.
+ */
+static void cache_rbio_pages(struct btrfs_raid_bio *rbio)
+{
+	int i;
+	int ret;
+
+	ret = alloc_rbio_pages(rbio);
+	if (ret)
+		return;
+
+	for (i = 0; i < rbio->nr_sectors; i++) {
+		/* Some range not covered by bio (partial write), skip it */
+		if (!rbio->bio_sectors[i].page)
+			continue;
+
+		ASSERT(rbio->stripe_sectors[i].page);
+		memcpy_page(rbio->stripe_sectors[i].page,
+			    rbio->stripe_sectors[i].pgoff,
+			    rbio->bio_sectors[i].page,
+			    rbio->bio_sectors[i].pgoff,
+			    rbio->bioc->fs_info->sectorsize);
+		rbio->stripe_sectors[i].uptodate = 1;
+	}
+	set_bit(RBIO_CACHE_READY_BIT, &rbio->flags);
+}
+
+/*
+ * we hash on the first logical address of the stripe
+ */
+static int rbio_bucket(struct btrfs_raid_bio *rbio)
+{
+	u64 num = rbio->bioc->raid_map[0];
+
+	/*
+	 * we shift down quite a bit.  We're using byte
+	 * addressing, and most of the lower bits are zeros.
+	 * This tends to upset hash_64, and it consistently
+	 * returns just one or two different values.
+	 *
+	 * shifting off the lower bits fixes things.
+	 */
+	return hash_64(num >> 16, BTRFS_STRIPE_HASH_TABLE_BITS);
+}
+
+static bool full_page_sectors_uptodate(struct btrfs_raid_bio *rbio,
+				       unsigned int page_nr)
+{
+	const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
+	const u32 sectors_per_page = PAGE_SIZE / sectorsize;
+	int i;
+
+	ASSERT(page_nr < rbio->nr_pages);
+
+	for (i = sectors_per_page * page_nr;
+	     i < sectors_per_page * page_nr + sectors_per_page;
+	     i++) {
+		if (!rbio->stripe_sectors[i].uptodate)
+			return false;
+	}
+	return true;
+}
+
+/*
+ * Update the stripe_sectors[] array to use correct page and pgoff
+ *
+ * Should be called every time any page pointer in stripes_pages[] got modified.
+ */
+static void index_stripe_sectors(struct btrfs_raid_bio *rbio)
+{
+	const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
+	u32 offset;
+	int i;
+
+	for (i = 0, offset = 0; i < rbio->nr_sectors; i++, offset += sectorsize) {
+		int page_index = offset >> PAGE_SHIFT;
+
+		ASSERT(page_index < rbio->nr_pages);
+		rbio->stripe_sectors[i].page = rbio->stripe_pages[page_index];
+		rbio->stripe_sectors[i].pgoff = offset_in_page(offset);
+	}
+}
+
+static void steal_rbio_page(struct btrfs_raid_bio *src,
+			    struct btrfs_raid_bio *dest, int page_nr)
+{
+	const u32 sectorsize = src->bioc->fs_info->sectorsize;
+	const u32 sectors_per_page = PAGE_SIZE / sectorsize;
+	int i;
+
+	if (dest->stripe_pages[page_nr])
+		__free_page(dest->stripe_pages[page_nr]);
+	dest->stripe_pages[page_nr] = src->stripe_pages[page_nr];
+	src->stripe_pages[page_nr] = NULL;
+
+	/* Also update the sector->uptodate bits. */
+	for (i = sectors_per_page * page_nr;
+	     i < sectors_per_page * page_nr + sectors_per_page; i++)
+		dest->stripe_sectors[i].uptodate = true;
+}
+
+/*
+ * Stealing an rbio means taking all the uptodate pages from the stripe array
+ * in the source rbio and putting them into the destination rbio.
+ *
+ * This will also update the involved stripe_sectors[] which are referring to
+ * the old pages.
+ */
+static void steal_rbio(struct btrfs_raid_bio *src, struct btrfs_raid_bio *dest)
+{
+	int i;
+	struct page *s;
+
+	if (!test_bit(RBIO_CACHE_READY_BIT, &src->flags))
+		return;
+
+	for (i = 0; i < dest->nr_pages; i++) {
+		s = src->stripe_pages[i];
+		if (!s || !full_page_sectors_uptodate(src, i))
+			continue;
+
+		steal_rbio_page(src, dest, i);
+	}
+	index_stripe_sectors(dest);
+	index_stripe_sectors(src);
+}
+
+/*
+ * merging means we take the bio_list from the victim and
+ * splice it into the destination.  The victim should
+ * be discarded afterwards.
+ *
+ * must be called with dest->rbio_list_lock held
+ */
+static void merge_rbio(struct btrfs_raid_bio *dest,
+		       struct btrfs_raid_bio *victim)
+{
+	bio_list_merge(&dest->bio_list, &victim->bio_list);
+	dest->bio_list_bytes += victim->bio_list_bytes;
+	/* Also inherit the bitmaps from @victim. */
+	bitmap_or(&dest->dbitmap, &victim->dbitmap, &dest->dbitmap,
+		  dest->stripe_nsectors);
+	bio_list_init(&victim->bio_list);
+}
+
+/*
+ * used to prune items that are in the cache.  The caller
+ * must hold the hash table lock.
+ */
+static void __remove_rbio_from_cache(struct btrfs_raid_bio *rbio)
+{
+	int bucket = rbio_bucket(rbio);
+	struct btrfs_stripe_hash_table *table;
+	struct btrfs_stripe_hash *h;
+	int freeit = 0;
+
+	/*
+	 * check the bit again under the hash table lock.
+	 */
+	if (!test_bit(RBIO_CACHE_BIT, &rbio->flags))
+		return;
+
+	table = rbio->bioc->fs_info->stripe_hash_table;
+	h = table->table + bucket;
+
+	/* hold the lock for the bucket because we may be
+	 * removing it from the hash table
+	 */
+	spin_lock(&h->lock);
+
+	/*
+	 * hold the lock for the bio list because we need
+	 * to make sure the bio list is empty
+	 */
+	spin_lock(&rbio->bio_list_lock);
+
+	if (test_and_clear_bit(RBIO_CACHE_BIT, &rbio->flags)) {
+		list_del_init(&rbio->stripe_cache);
+		table->cache_size -= 1;
+		freeit = 1;
+
+		/* if the bio list isn't empty, this rbio is
+		 * still involved in an IO.  We take it out
+		 * of the cache list, and drop the ref that
+		 * was held for the list.
+		 *
+		 * If the bio_list was empty, we also remove
+		 * the rbio from the hash_table, and drop
+		 * the corresponding ref
+		 */
+		if (bio_list_empty(&rbio->bio_list)) {
+			if (!list_empty(&rbio->hash_list)) {
+				list_del_init(&rbio->hash_list);
+				refcount_dec(&rbio->refs);
+				BUG_ON(!list_empty(&rbio->plug_list));
+			}
+		}
+	}
+
+	spin_unlock(&rbio->bio_list_lock);
+	spin_unlock(&h->lock);
+
+	if (freeit)
+		__free_raid_bio(rbio);
+}
+
+/*
+ * prune a given rbio from the cache
+ */
+static void remove_rbio_from_cache(struct btrfs_raid_bio *rbio)
+{
+	struct btrfs_stripe_hash_table *table;
+	unsigned long flags;
+
+	if (!test_bit(RBIO_CACHE_BIT, &rbio->flags))
+		return;
+
+	table = rbio->bioc->fs_info->stripe_hash_table;
+
+	spin_lock_irqsave(&table->cache_lock, flags);
+	__remove_rbio_from_cache(rbio);
+	spin_unlock_irqrestore(&table->cache_lock, flags);
+}
+
+/*
+ * remove everything in the cache
+ */
+static void btrfs_clear_rbio_cache(struct btrfs_fs_info *info)
+{
+	struct btrfs_stripe_hash_table *table;
+	unsigned long flags;
+	struct btrfs_raid_bio *rbio;
+
+	table = info->stripe_hash_table;
+
+	spin_lock_irqsave(&table->cache_lock, flags);
+	while (!list_empty(&table->stripe_cache)) {
+		rbio = list_entry(table->stripe_cache.next,
+				  struct btrfs_raid_bio,
+				  stripe_cache);
+		__remove_rbio_from_cache(rbio);
+	}
+	spin_unlock_irqrestore(&table->cache_lock, flags);
+}
+
+/*
+ * remove all cached entries and free the hash table
+ * used by unmount
+ */
+void btrfs_free_stripe_hash_table(struct btrfs_fs_info *info)
+{
+	if (!info->stripe_hash_table)
+		return;
+	btrfs_clear_rbio_cache(info);
+	kvfree(info->stripe_hash_table);
+	info->stripe_hash_table = NULL;
+}
+
+/*
+ * insert an rbio into the stripe cache.  It
+ * must have already been prepared by calling
+ * cache_rbio_pages
+ *
+ * If this rbio was already cached, it gets
+ * moved to the front of the lru.
+ *
+ * If the size of the rbio cache is too big, we
+ * prune an item.
+ */
+static void cache_rbio(struct btrfs_raid_bio *rbio)
+{
+	struct btrfs_stripe_hash_table *table;
+	unsigned long flags;
+
+	if (!test_bit(RBIO_CACHE_READY_BIT, &rbio->flags))
+		return;
+
+	table = rbio->bioc->fs_info->stripe_hash_table;
+
+	spin_lock_irqsave(&table->cache_lock, flags);
+	spin_lock(&rbio->bio_list_lock);
+
+	/* bump our ref if we were not in the list before */
+	if (!test_and_set_bit(RBIO_CACHE_BIT, &rbio->flags))
+		refcount_inc(&rbio->refs);
+
+	if (!list_empty(&rbio->stripe_cache)){
+		list_move(&rbio->stripe_cache, &table->stripe_cache);
+	} else {
+		list_add(&rbio->stripe_cache, &table->stripe_cache);
+		table->cache_size += 1;
+	}
+
+	spin_unlock(&rbio->bio_list_lock);
+
+	if (table->cache_size > RBIO_CACHE_SIZE) {
+		struct btrfs_raid_bio *found;
+
+		found = list_entry(table->stripe_cache.prev,
+				  struct btrfs_raid_bio,
+				  stripe_cache);
+
+		if (found != rbio)
+			__remove_rbio_from_cache(found);
+	}
+
+	spin_unlock_irqrestore(&table->cache_lock, flags);
+}
+
+/*
+ * helper function to run the xor_blocks api.  It is only
+ * able to do MAX_XOR_BLOCKS at a time, so we need to
+ * loop through.
+ */
+static void run_xor(void **pages, int src_cnt, ssize_t len)
+{
+	int src_off = 0;
+	int xor_src_cnt = 0;
+	void *dest = pages[src_cnt];
+
+	while(src_cnt > 0) {
+		xor_src_cnt = min(src_cnt, MAX_XOR_BLOCKS);
+		xor_blocks(xor_src_cnt, len, dest, pages + src_off);
+
+		src_cnt -= xor_src_cnt;
+		src_off += xor_src_cnt;
+	}
+}
+
+/*
+ * Returns true if the bio list inside this rbio covers an entire stripe (no
+ * rmw required).
+ */
+static int rbio_is_full(struct btrfs_raid_bio *rbio)
+{
+	unsigned long flags;
+	unsigned long size = rbio->bio_list_bytes;
+	int ret = 1;
+
+	spin_lock_irqsave(&rbio->bio_list_lock, flags);
+	if (size != rbio->nr_data * BTRFS_STRIPE_LEN)
+		ret = 0;
+	BUG_ON(size > rbio->nr_data * BTRFS_STRIPE_LEN);
+	spin_unlock_irqrestore(&rbio->bio_list_lock, flags);
+
+	return ret;
+}
+
+/*
+ * returns 1 if it is safe to merge two rbios together.
+ * The merging is safe if the two rbios correspond to
+ * the same stripe and if they are both going in the same
+ * direction (read vs write), and if neither one is
+ * locked for final IO
+ *
+ * The caller is responsible for locking such that
+ * rmw_locked is safe to test
+ */
+static int rbio_can_merge(struct btrfs_raid_bio *last,
+			  struct btrfs_raid_bio *cur)
+{
+	if (test_bit(RBIO_RMW_LOCKED_BIT, &last->flags) ||
+	    test_bit(RBIO_RMW_LOCKED_BIT, &cur->flags))
+		return 0;
+
+	/*
+	 * we can't merge with cached rbios, since the
+	 * idea is that when we merge the destination
+	 * rbio is going to run our IO for us.  We can
+	 * steal from cached rbios though, other functions
+	 * handle that.
+	 */
+	if (test_bit(RBIO_CACHE_BIT, &last->flags) ||
+	    test_bit(RBIO_CACHE_BIT, &cur->flags))
+		return 0;
+
+	if (last->bioc->raid_map[0] != cur->bioc->raid_map[0])
+		return 0;
+
+	/* we can't merge with different operations */
+	if (last->operation != cur->operation)
+		return 0;
+	/*
+	 * We've need read the full stripe from the drive.
+	 * check and repair the parity and write the new results.
+	 *
+	 * We're not allowed to add any new bios to the
+	 * bio list here, anyone else that wants to
+	 * change this stripe needs to do their own rmw.
+	 */
+	if (last->operation == BTRFS_RBIO_PARITY_SCRUB)
+		return 0;
+
+	if (last->operation == BTRFS_RBIO_REBUILD_MISSING)
+		return 0;
+
+	if (last->operation == BTRFS_RBIO_READ_REBUILD) {
+		int fa = last->faila;
+		int fb = last->failb;
+		int cur_fa = cur->faila;
+		int cur_fb = cur->failb;
+
+		if (last->faila >= last->failb) {
+			fa = last->failb;
+			fb = last->faila;
+		}
+
+		if (cur->faila >= cur->failb) {
+			cur_fa = cur->failb;
+			cur_fb = cur->faila;
+		}
+
+		if (fa != cur_fa || fb != cur_fb)
+			return 0;
+	}
+	return 1;
+}
+
+static unsigned int rbio_stripe_sector_index(const struct btrfs_raid_bio *rbio,
+					     unsigned int stripe_nr,
+					     unsigned int sector_nr)
+{
+	ASSERT(stripe_nr < rbio->real_stripes);
+	ASSERT(sector_nr < rbio->stripe_nsectors);
+
+	return stripe_nr * rbio->stripe_nsectors + sector_nr;
+}
+
+/* Return a sector from rbio->stripe_sectors, not from the bio list */
+static struct sector_ptr *rbio_stripe_sector(const struct btrfs_raid_bio *rbio,
+					     unsigned int stripe_nr,
+					     unsigned int sector_nr)
+{
+	return &rbio->stripe_sectors[rbio_stripe_sector_index(rbio, stripe_nr,
+							      sector_nr)];
+}
+
+/* Grab a sector inside P stripe */
+static struct sector_ptr *rbio_pstripe_sector(const struct btrfs_raid_bio *rbio,
+					      unsigned int sector_nr)
+{
+	return rbio_stripe_sector(rbio, rbio->nr_data, sector_nr);
+}
+
+/* Grab a sector inside Q stripe, return NULL if not RAID6 */
+static struct sector_ptr *rbio_qstripe_sector(const struct btrfs_raid_bio *rbio,
+					      unsigned int sector_nr)
+{
+	if (rbio->nr_data + 1 == rbio->real_stripes)
+		return NULL;
+	return rbio_stripe_sector(rbio, rbio->nr_data + 1, sector_nr);
+}
+
+/*
+ * The first stripe in the table for a logical address
+ * has the lock.  rbios are added in one of three ways:
+ *
+ * 1) Nobody has the stripe locked yet.  The rbio is given
+ * the lock and 0 is returned.  The caller must start the IO
+ * themselves.
+ *
+ * 2) Someone has the stripe locked, but we're able to merge
+ * with the lock owner.  The rbio is freed and the IO will
+ * start automatically along with the existing rbio.  1 is returned.
+ *
+ * 3) Someone has the stripe locked, but we're not able to merge.
+ * The rbio is added to the lock owner's plug list, or merged into
+ * an rbio already on the plug list.  When the lock owner unlocks,
+ * the next rbio on the list is run and the IO is started automatically.
+ * 1 is returned
+ *
+ * If we return 0, the caller still owns the rbio and must continue with
+ * IO submission.  If we return 1, the caller must assume the rbio has
+ * already been freed.
+ */
+static noinline int lock_stripe_add(struct btrfs_raid_bio *rbio)
+{
+	struct btrfs_stripe_hash *h;
+	struct btrfs_raid_bio *cur;
+	struct btrfs_raid_bio *pending;
+	unsigned long flags;
+	struct btrfs_raid_bio *freeit = NULL;
+	struct btrfs_raid_bio *cache_drop = NULL;
+	int ret = 0;
+
+	h = rbio->bioc->fs_info->stripe_hash_table->table + rbio_bucket(rbio);
+
+	spin_lock_irqsave(&h->lock, flags);
+	list_for_each_entry(cur, &h->hash_list, hash_list) {
+		if (cur->bioc->raid_map[0] != rbio->bioc->raid_map[0])
+			continue;
+
+		spin_lock(&cur->bio_list_lock);
+
+		/* Can we steal this cached rbio's pages? */
+		if (bio_list_empty(&cur->bio_list) &&
+		    list_empty(&cur->plug_list) &&
+		    test_bit(RBIO_CACHE_BIT, &cur->flags) &&
+		    !test_bit(RBIO_RMW_LOCKED_BIT, &cur->flags)) {
+			list_del_init(&cur->hash_list);
+			refcount_dec(&cur->refs);
+
+			steal_rbio(cur, rbio);
+			cache_drop = cur;
+			spin_unlock(&cur->bio_list_lock);
+
+			goto lockit;
+		}
+
+		/* Can we merge into the lock owner? */
+		if (rbio_can_merge(cur, rbio)) {
+			merge_rbio(cur, rbio);
+			spin_unlock(&cur->bio_list_lock);
+			freeit = rbio;
+			ret = 1;
+			goto out;
+		}
+
+
+		/*
+		 * We couldn't merge with the running rbio, see if we can merge
+		 * with the pending ones.  We don't have to check for rmw_locked
+		 * because there is no way they are inside finish_rmw right now
+		 */
+		list_for_each_entry(pending, &cur->plug_list, plug_list) {
+			if (rbio_can_merge(pending, rbio)) {
+				merge_rbio(pending, rbio);
+				spin_unlock(&cur->bio_list_lock);
+				freeit = rbio;
+				ret = 1;
+				goto out;
+			}
+		}
+
+		/*
+		 * No merging, put us on the tail of the plug list, our rbio
+		 * will be started with the currently running rbio unlocks
+		 */
+		list_add_tail(&rbio->plug_list, &cur->plug_list);
+		spin_unlock(&cur->bio_list_lock);
+		ret = 1;
+		goto out;
+	}
+lockit:
+	refcount_inc(&rbio->refs);
+	list_add(&rbio->hash_list, &h->hash_list);
+out:
+	spin_unlock_irqrestore(&h->lock, flags);
+	if (cache_drop)
+		remove_rbio_from_cache(cache_drop);
+	if (freeit)
+		__free_raid_bio(freeit);
+	return ret;
+}
+
+/*
+ * called as rmw or parity rebuild is completed.  If the plug list has more
+ * rbios waiting for this stripe, the next one on the list will be started
+ */
+static noinline void unlock_stripe(struct btrfs_raid_bio *rbio)
+{
+	int bucket;
+	struct btrfs_stripe_hash *h;
+	unsigned long flags;
+	int keep_cache = 0;
+
+	bucket = rbio_bucket(rbio);
+	h = rbio->bioc->fs_info->stripe_hash_table->table + bucket;
+
+	if (list_empty(&rbio->plug_list))
+		cache_rbio(rbio);
+
+	spin_lock_irqsave(&h->lock, flags);
+	spin_lock(&rbio->bio_list_lock);
+
+	if (!list_empty(&rbio->hash_list)) {
+		/*
+		 * if we're still cached and there is no other IO
+		 * to perform, just leave this rbio here for others
+		 * to steal from later
+		 */
+		if (list_empty(&rbio->plug_list) &&
+		    test_bit(RBIO_CACHE_BIT, &rbio->flags)) {
+			keep_cache = 1;
+			clear_bit(RBIO_RMW_LOCKED_BIT, &rbio->flags);
+			BUG_ON(!bio_list_empty(&rbio->bio_list));
+			goto done;
+		}
+
+		list_del_init(&rbio->hash_list);
+		refcount_dec(&rbio->refs);
+
+		/*
+		 * we use the plug list to hold all the rbios
+		 * waiting for the chance to lock this stripe.
+		 * hand the lock over to one of them.
+		 */
+		if (!list_empty(&rbio->plug_list)) {
+			struct btrfs_raid_bio *next;
+			struct list_head *head = rbio->plug_list.next;
+
+			next = list_entry(head, struct btrfs_raid_bio,
+					  plug_list);
+
+			list_del_init(&rbio->plug_list);
+
+			list_add(&next->hash_list, &h->hash_list);
+			refcount_inc(&next->refs);
+			spin_unlock(&rbio->bio_list_lock);
+			spin_unlock_irqrestore(&h->lock, flags);
+
+			if (next->operation == BTRFS_RBIO_READ_REBUILD)
+				start_async_work(next, read_rebuild_work);
+			else if (next->operation == BTRFS_RBIO_REBUILD_MISSING) {
+				steal_rbio(rbio, next);
+				start_async_work(next, read_rebuild_work);
+			} else if (next->operation == BTRFS_RBIO_WRITE) {
+				steal_rbio(rbio, next);
+				start_async_work(next, rmw_work);
+			} else if (next->operation == BTRFS_RBIO_PARITY_SCRUB) {
+				steal_rbio(rbio, next);
+				start_async_work(next, scrub_parity_work);
+			}
+
+			goto done_nolock;
+		}
+	}
+done:
+	spin_unlock(&rbio->bio_list_lock);
+	spin_unlock_irqrestore(&h->lock, flags);
+
+done_nolock:
+	if (!keep_cache)
+		remove_rbio_from_cache(rbio);
+}
+
+static void __free_raid_bio(struct btrfs_raid_bio *rbio)
+{
+	int i;
+
+	if (!refcount_dec_and_test(&rbio->refs))
+		return;
+
+	WARN_ON(!list_empty(&rbio->stripe_cache));
+	WARN_ON(!list_empty(&rbio->hash_list));
+	WARN_ON(!bio_list_empty(&rbio->bio_list));
+
+	for (i = 0; i < rbio->nr_pages; i++) {
+		if (rbio->stripe_pages[i]) {
+			__free_page(rbio->stripe_pages[i]);
+			rbio->stripe_pages[i] = NULL;
+		}
+	}
+
+	btrfs_put_bioc(rbio->bioc);
+	kfree(rbio);
+}
+
+static void rbio_endio_bio_list(struct bio *cur, blk_status_t err)
+{
+	struct bio *next;
+
+	while (cur) {
+		next = cur->bi_next;
+		cur->bi_next = NULL;
+		cur->bi_status = err;
+		bio_endio(cur);
+		cur = next;
+	}
+}
+
+/*
+ * this frees the rbio and runs through all the bios in the
+ * bio_list and calls end_io on them
+ */
+static void rbio_orig_end_io(struct btrfs_raid_bio *rbio, blk_status_t err)
+{
+	struct bio *cur = bio_list_get(&rbio->bio_list);
+	struct bio *extra;
+
+	/*
+	 * Clear the data bitmap, as the rbio may be cached for later usage.
+	 * do this before before unlock_stripe() so there will be no new bio
+	 * for this bio.
+	 */
+	bitmap_clear(&rbio->dbitmap, 0, rbio->stripe_nsectors);
+
+	/*
+	 * At this moment, rbio->bio_list is empty, however since rbio does not
+	 * always have RBIO_RMW_LOCKED_BIT set and rbio is still linked on the
+	 * hash list, rbio may be merged with others so that rbio->bio_list
+	 * becomes non-empty.
+	 * Once unlock_stripe() is done, rbio->bio_list will not be updated any
+	 * more and we can call bio_endio() on all queued bios.
+	 */
+	unlock_stripe(rbio);
+	extra = bio_list_get(&rbio->bio_list);
+	__free_raid_bio(rbio);
+
+	rbio_endio_bio_list(cur, err);
+	if (extra)
+		rbio_endio_bio_list(extra, err);
+}
+
+/*
+ * end io function used by finish_rmw.  When we finally
+ * get here, we've written a full stripe
+ */
+static void raid_write_end_io(struct bio *bio)
+{
+	struct btrfs_raid_bio *rbio = bio->bi_private;
+	blk_status_t err = bio->bi_status;
+	int max_errors;
+
+	if (err)
+		fail_bio_stripe(rbio, bio);
+
+	bio_put(bio);
+
+	if (!atomic_dec_and_test(&rbio->stripes_pending))
+		return;
+
+	err = BLK_STS_OK;
+
+	/* OK, we have read all the stripes we need to. */
+	max_errors = (rbio->operation == BTRFS_RBIO_PARITY_SCRUB) ?
+		     0 : rbio->bioc->max_errors;
+	if (atomic_read(&rbio->error) > max_errors)
+		err = BLK_STS_IOERR;
+
+	rbio_orig_end_io(rbio, err);
+}
+
+/**
+ * Get a sector pointer specified by its @stripe_nr and @sector_nr
+ *
+ * @rbio:               The raid bio
+ * @stripe_nr:          Stripe number, valid range [0, real_stripe)
+ * @sector_nr:		Sector number inside the stripe,
+ *			valid range [0, stripe_nsectors)
+ * @bio_list_only:      Whether to use sectors inside the bio list only.
+ *
+ * The read/modify/write code wants to reuse the original bio page as much
+ * as possible, and only use stripe_sectors as fallback.
+ */
+static struct sector_ptr *sector_in_rbio(struct btrfs_raid_bio *rbio,
+					 int stripe_nr, int sector_nr,
+					 bool bio_list_only)
+{
+	struct sector_ptr *sector;
+	int index;
+
+	ASSERT(stripe_nr >= 0 && stripe_nr < rbio->real_stripes);
+	ASSERT(sector_nr >= 0 && sector_nr < rbio->stripe_nsectors);
+
+	index = stripe_nr * rbio->stripe_nsectors + sector_nr;
+	ASSERT(index >= 0 && index < rbio->nr_sectors);
+
+	spin_lock_irq(&rbio->bio_list_lock);
+	sector = &rbio->bio_sectors[index];
+	if (sector->page || bio_list_only) {
+		/* Don't return sector without a valid page pointer */
+		if (!sector->page)
+			sector = NULL;
+		spin_unlock_irq(&rbio->bio_list_lock);
+		return sector;
+	}
+	spin_unlock_irq(&rbio->bio_list_lock);
+
+	return &rbio->stripe_sectors[index];
+}
+
+/*
+ * allocation and initial setup for the btrfs_raid_bio.  Not
+ * this does not allocate any pages for rbio->pages.
+ */
+static struct btrfs_raid_bio *alloc_rbio(struct btrfs_fs_info *fs_info,
+					 struct btrfs_io_context *bioc)
+{
+	const unsigned int real_stripes = bioc->num_stripes - bioc->num_tgtdevs;
+	const unsigned int stripe_npages = BTRFS_STRIPE_LEN >> PAGE_SHIFT;
+	const unsigned int num_pages = stripe_npages * real_stripes;
+	const unsigned int stripe_nsectors =
+		BTRFS_STRIPE_LEN >> fs_info->sectorsize_bits;
+	const unsigned int num_sectors = stripe_nsectors * real_stripes;
+	struct btrfs_raid_bio *rbio;
+	void *p;
+
+	/* PAGE_SIZE must also be aligned to sectorsize for subpage support */
+	ASSERT(IS_ALIGNED(PAGE_SIZE, fs_info->sectorsize));
+	/*
+	 * Our current stripe len should be fixed to 64k thus stripe_nsectors
+	 * (at most 16) should be no larger than BITS_PER_LONG.
+	 */
+	ASSERT(stripe_nsectors <= BITS_PER_LONG);
+
+	rbio = kzalloc(sizeof(*rbio) +
+		       sizeof(*rbio->stripe_pages) * num_pages +
+		       sizeof(*rbio->bio_sectors) * num_sectors +
+		       sizeof(*rbio->stripe_sectors) * num_sectors +
+		       sizeof(*rbio->finish_pointers) * real_stripes,
+		       GFP_NOFS);
+	if (!rbio)
+		return ERR_PTR(-ENOMEM);
+
+	bio_list_init(&rbio->bio_list);
+	INIT_LIST_HEAD(&rbio->plug_list);
+	spin_lock_init(&rbio->bio_list_lock);
+	INIT_LIST_HEAD(&rbio->stripe_cache);
+	INIT_LIST_HEAD(&rbio->hash_list);
+	btrfs_get_bioc(bioc);
+	rbio->bioc = bioc;
+	rbio->nr_pages = num_pages;
+	rbio->nr_sectors = num_sectors;
+	rbio->real_stripes = real_stripes;
+	rbio->stripe_npages = stripe_npages;
+	rbio->stripe_nsectors = stripe_nsectors;
+	rbio->faila = -1;
+	rbio->failb = -1;
+	refcount_set(&rbio->refs, 1);
+	atomic_set(&rbio->error, 0);
+	atomic_set(&rbio->stripes_pending, 0);
+
+	/*
+	 * The stripe_pages, bio_sectors, etc arrays point to the extra memory
+	 * we allocated past the end of the rbio.
+	 */
+	p = rbio + 1;
+#define CONSUME_ALLOC(ptr, count)	do {				\
+		ptr = p;						\
+		p = (unsigned char *)p + sizeof(*(ptr)) * (count);	\
+	} while (0)
+	CONSUME_ALLOC(rbio->stripe_pages, num_pages);
+	CONSUME_ALLOC(rbio->bio_sectors, num_sectors);
+	CONSUME_ALLOC(rbio->stripe_sectors, num_sectors);
+	CONSUME_ALLOC(rbio->finish_pointers, real_stripes);
+#undef  CONSUME_ALLOC
+
+	ASSERT(btrfs_nr_parity_stripes(bioc->map_type));
+	rbio->nr_data = real_stripes - btrfs_nr_parity_stripes(bioc->map_type);
+
+	return rbio;
+}
+
+/* allocate pages for all the stripes in the bio, including parity */
+static int alloc_rbio_pages(struct btrfs_raid_bio *rbio)
+{
+	int ret;
+
+	ret = btrfs_alloc_page_array(rbio->nr_pages, rbio->stripe_pages);
+	if (ret < 0)
+		return ret;
+	/* Mapping all sectors */
+	index_stripe_sectors(rbio);
+	return 0;
+}
+
+/* only allocate pages for p/q stripes */
+static int alloc_rbio_parity_pages(struct btrfs_raid_bio *rbio)
+{
+	const int data_pages = rbio->nr_data * rbio->stripe_npages;
+	int ret;
+
+	ret = btrfs_alloc_page_array(rbio->nr_pages - data_pages,
+				     rbio->stripe_pages + data_pages);
+	if (ret < 0)
+		return ret;
+
+	index_stripe_sectors(rbio);
+	return 0;
+}
+
+/*
+ * Add a single sector @sector into our list of bios for IO.
+ *
+ * Return 0 if everything went well.
+ * Return <0 for error.
+ */
+static int rbio_add_io_sector(struct btrfs_raid_bio *rbio,
+			      struct bio_list *bio_list,
+			      struct sector_ptr *sector,
+			      unsigned int stripe_nr,
+			      unsigned int sector_nr,
+			      enum req_op op)
+{
+	const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
+	struct bio *last = bio_list->tail;
+	int ret;
+	struct bio *bio;
+	struct btrfs_io_stripe *stripe;
+	u64 disk_start;
+
+	/*
+	 * Note: here stripe_nr has taken device replace into consideration,
+	 * thus it can be larger than rbio->real_stripe.
+	 * So here we check against bioc->num_stripes, not rbio->real_stripes.
+	 */
+	ASSERT(stripe_nr >= 0 && stripe_nr < rbio->bioc->num_stripes);
+	ASSERT(sector_nr >= 0 && sector_nr < rbio->stripe_nsectors);
+	ASSERT(sector->page);
+
+	stripe = &rbio->bioc->stripes[stripe_nr];
+	disk_start = stripe->physical + sector_nr * sectorsize;
+
+	/* if the device is missing, just fail this stripe */
+	if (!stripe->dev->bdev)
+		return fail_rbio_index(rbio, stripe_nr);
+
+	/* see if we can add this page onto our existing bio */
+	if (last) {
+		u64 last_end = last->bi_iter.bi_sector << 9;
+		last_end += last->bi_iter.bi_size;
+
+		/*
+		 * we can't merge these if they are from different
+		 * devices or if they are not contiguous
+		 */
+		if (last_end == disk_start && !last->bi_status &&
+		    last->bi_bdev == stripe->dev->bdev) {
+			ret = bio_add_page(last, sector->page, sectorsize,
+					   sector->pgoff);
+			if (ret == sectorsize)
+				return 0;
+		}
+	}
+
+	/* put a new bio on the list */
+	bio = bio_alloc(stripe->dev->bdev,
+			max(BTRFS_STRIPE_LEN >> PAGE_SHIFT, 1),
+			op, GFP_NOFS);
+	bio->bi_iter.bi_sector = disk_start >> 9;
+	bio->bi_private = rbio;
+
+	bio_add_page(bio, sector->page, sectorsize, sector->pgoff);
+	bio_list_add(bio_list, bio);
+	return 0;
+}
+
+/*
+ * while we're doing the read/modify/write cycle, we could
+ * have errors in reading pages off the disk.  This checks
+ * for errors and if we're not able to read the page it'll
+ * trigger parity reconstruction.  The rmw will be finished
+ * after we've reconstructed the failed stripes
+ */
+static void validate_rbio_for_rmw(struct btrfs_raid_bio *rbio)
+{
+	if (rbio->faila >= 0 || rbio->failb >= 0) {
+		BUG_ON(rbio->faila == rbio->real_stripes - 1);
+		__raid56_parity_recover(rbio);
+	} else {
+		finish_rmw(rbio);
+	}
+}
+
+static void index_one_bio(struct btrfs_raid_bio *rbio, struct bio *bio)
+{
+	const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
+	struct bio_vec bvec;
+	struct bvec_iter iter;
+	u32 offset = (bio->bi_iter.bi_sector << SECTOR_SHIFT) -
+		     rbio->bioc->raid_map[0];
+
+	bio_for_each_segment(bvec, bio, iter) {
+		u32 bvec_offset;
+
+		for (bvec_offset = 0; bvec_offset < bvec.bv_len;
+		     bvec_offset += sectorsize, offset += sectorsize) {
+			int index = offset / sectorsize;
+			struct sector_ptr *sector = &rbio->bio_sectors[index];
+
+			sector->page = bvec.bv_page;
+			sector->pgoff = bvec.bv_offset + bvec_offset;
+			ASSERT(sector->pgoff < PAGE_SIZE);
+		}
+	}
+}
+
+/*
+ * helper function to walk our bio list and populate the bio_pages array with
+ * the result.  This seems expensive, but it is faster than constantly
+ * searching through the bio list as we setup the IO in finish_rmw or stripe
+ * reconstruction.
+ *
+ * This must be called before you trust the answers from page_in_rbio
+ */
+static void index_rbio_pages(struct btrfs_raid_bio *rbio)
+{
+	struct bio *bio;
+
+	spin_lock_irq(&rbio->bio_list_lock);
+	bio_list_for_each(bio, &rbio->bio_list)
+		index_one_bio(rbio, bio);
+
+	spin_unlock_irq(&rbio->bio_list_lock);
+}
+
+static void bio_get_trace_info(struct btrfs_raid_bio *rbio, struct bio *bio,
+			       struct raid56_bio_trace_info *trace_info)
+{
+	const struct btrfs_io_context *bioc = rbio->bioc;
+	int i;
+
+	ASSERT(bioc);
+
+	/* We rely on bio->bi_bdev to find the stripe number. */
+	if (!bio->bi_bdev)
+		goto not_found;
+
+	for (i = 0; i < bioc->num_stripes; i++) {
+		if (bio->bi_bdev != bioc->stripes[i].dev->bdev)
+			continue;
+		trace_info->stripe_nr = i;
+		trace_info->devid = bioc->stripes[i].dev->devid;
+		trace_info->offset = (bio->bi_iter.bi_sector << SECTOR_SHIFT) -
+				     bioc->stripes[i].physical;
+		return;
+	}
+
+not_found:
+	trace_info->devid = -1;
+	trace_info->offset = -1;
+	trace_info->stripe_nr = -1;
+}
+
+/*
+ * this is called from one of two situations.  We either
+ * have a full stripe from the higher layers, or we've read all
+ * the missing bits off disk.
+ *
+ * This will calculate the parity and then send down any
+ * changed blocks.
+ */
+static noinline void finish_rmw(struct btrfs_raid_bio *rbio)
+{
+	struct btrfs_io_context *bioc = rbio->bioc;
+	const u32 sectorsize = bioc->fs_info->sectorsize;
+	void **pointers = rbio->finish_pointers;
+	int nr_data = rbio->nr_data;
+	/* The total sector number inside the full stripe. */
+	int total_sector_nr;
+	int stripe;
+	/* Sector number inside a stripe. */
+	int sectornr;
+	bool has_qstripe;
+	struct bio_list bio_list;
+	struct bio *bio;
+	int ret;
+
+	bio_list_init(&bio_list);
+
+	if (rbio->real_stripes - rbio->nr_data == 1)
+		has_qstripe = false;
+	else if (rbio->real_stripes - rbio->nr_data == 2)
+		has_qstripe = true;
+	else
+		BUG();
+
+	/* We should have at least one data sector. */
+	ASSERT(bitmap_weight(&rbio->dbitmap, rbio->stripe_nsectors));
+
+	/* at this point we either have a full stripe,
+	 * or we've read the full stripe from the drive.
+	 * recalculate the parity and write the new results.
+	 *
+	 * We're not allowed to add any new bios to the
+	 * bio list here, anyone else that wants to
+	 * change this stripe needs to do their own rmw.
+	 */
+	spin_lock_irq(&rbio->bio_list_lock);
+	set_bit(RBIO_RMW_LOCKED_BIT, &rbio->flags);
+	spin_unlock_irq(&rbio->bio_list_lock);
+
+	atomic_set(&rbio->error, 0);
+
+	/*
+	 * now that we've set rmw_locked, run through the
+	 * bio list one last time and map the page pointers
+	 *
+	 * We don't cache full rbios because we're assuming
+	 * the higher layers are unlikely to use this area of
+	 * the disk again soon.  If they do use it again,
+	 * hopefully they will send another full bio.
+	 */
+	index_rbio_pages(rbio);
+	if (!rbio_is_full(rbio))
+		cache_rbio_pages(rbio);
+	else
+		clear_bit(RBIO_CACHE_READY_BIT, &rbio->flags);
+
+	for (sectornr = 0; sectornr < rbio->stripe_nsectors; sectornr++) {
+		struct sector_ptr *sector;
+
+		/* First collect one sector from each data stripe */
+		for (stripe = 0; stripe < nr_data; stripe++) {
+			sector = sector_in_rbio(rbio, stripe, sectornr, 0);
+			pointers[stripe] = kmap_local_page(sector->page) +
+					   sector->pgoff;
+		}
+
+		/* Then add the parity stripe */
+		sector = rbio_pstripe_sector(rbio, sectornr);
+		sector->uptodate = 1;
+		pointers[stripe++] = kmap_local_page(sector->page) + sector->pgoff;
+
+		if (has_qstripe) {
+			/*
+			 * RAID6, add the qstripe and call the library function
+			 * to fill in our p/q
+			 */
+			sector = rbio_qstripe_sector(rbio, sectornr);
+			sector->uptodate = 1;
+			pointers[stripe++] = kmap_local_page(sector->page) +
+					     sector->pgoff;
+
+			raid6_call.gen_syndrome(rbio->real_stripes, sectorsize,
+						pointers);
+		} else {
+			/* raid5 */
+			memcpy(pointers[nr_data], pointers[0], sectorsize);
+			run_xor(pointers + 1, nr_data - 1, sectorsize);
+		}
+		for (stripe = stripe - 1; stripe >= 0; stripe--)
+			kunmap_local(pointers[stripe]);
+	}
+
+	/*
+	 * Start writing.  Make bios for everything from the higher layers (the
+	 * bio_list in our rbio) and our P/Q.  Ignore everything else.
+	 */
+	for (total_sector_nr = 0; total_sector_nr < rbio->nr_sectors;
+	     total_sector_nr++) {
+		struct sector_ptr *sector;
+
+		stripe = total_sector_nr / rbio->stripe_nsectors;
+		sectornr = total_sector_nr % rbio->stripe_nsectors;
+
+		/* This vertical stripe has no data, skip it. */
+		if (!test_bit(sectornr, &rbio->dbitmap))
+			continue;
+
+		if (stripe < rbio->nr_data) {
+			sector = sector_in_rbio(rbio, stripe, sectornr, 1);
+			if (!sector)
+				continue;
+		} else {
+			sector = rbio_stripe_sector(rbio, stripe, sectornr);
+		}
+
+		ret = rbio_add_io_sector(rbio, &bio_list, sector, stripe,
+					 sectornr, REQ_OP_WRITE);
+		if (ret)
+			goto cleanup;
+	}
+
+	if (likely(!bioc->num_tgtdevs))
+		goto write_data;
+
+	for (total_sector_nr = 0; total_sector_nr < rbio->nr_sectors;
+	     total_sector_nr++) {
+		struct sector_ptr *sector;
+
+		stripe = total_sector_nr / rbio->stripe_nsectors;
+		sectornr = total_sector_nr % rbio->stripe_nsectors;
+
+		if (!bioc->tgtdev_map[stripe]) {
+			/*
+			 * We can skip the whole stripe completely, note
+			 * total_sector_nr will be increased by one anyway.
+			 */
+			ASSERT(sectornr == 0);
+			total_sector_nr += rbio->stripe_nsectors - 1;
+			continue;
+		}
+
+		/* This vertical stripe has no data, skip it. */
+		if (!test_bit(sectornr, &rbio->dbitmap))
+			continue;
+
+		if (stripe < rbio->nr_data) {
+			sector = sector_in_rbio(rbio, stripe, sectornr, 1);
+			if (!sector)
+				continue;
+		} else {
+			sector = rbio_stripe_sector(rbio, stripe, sectornr);
+		}
+
+		ret = rbio_add_io_sector(rbio, &bio_list, sector,
+					 rbio->bioc->tgtdev_map[stripe],
+					 sectornr, REQ_OP_WRITE);
+		if (ret)
+			goto cleanup;
+	}
+
+write_data:
+	atomic_set(&rbio->stripes_pending, bio_list_size(&bio_list));
+	BUG_ON(atomic_read(&rbio->stripes_pending) == 0);
+
+	while ((bio = bio_list_pop(&bio_list))) {
+		bio->bi_end_io = raid_write_end_io;
+
+		if (trace_raid56_write_stripe_enabled()) {
+			struct raid56_bio_trace_info trace_info = { 0 };
+
+			bio_get_trace_info(rbio, bio, &trace_info);
+			trace_raid56_write_stripe(rbio, bio, &trace_info);
+		}
+		submit_bio(bio);
+	}
+	return;
+
+cleanup:
+	rbio_orig_end_io(rbio, BLK_STS_IOERR);
+
+	while ((bio = bio_list_pop(&bio_list)))
+		bio_put(bio);
+}
+
+/*
+ * helper to find the stripe number for a given bio.  Used to figure out which
+ * stripe has failed.  This expects the bio to correspond to a physical disk,
+ * so it looks up based on physical sector numbers.
+ */
+static int find_bio_stripe(struct btrfs_raid_bio *rbio,
+			   struct bio *bio)
+{
+	u64 physical = bio->bi_iter.bi_sector;
+	int i;
+	struct btrfs_io_stripe *stripe;
+
+	physical <<= 9;
+
+	for (i = 0; i < rbio->bioc->num_stripes; i++) {
+		stripe = &rbio->bioc->stripes[i];
+		if (in_range(physical, stripe->physical, BTRFS_STRIPE_LEN) &&
+		    stripe->dev->bdev && bio->bi_bdev == stripe->dev->bdev) {
+			return i;
+		}
+	}
+	return -1;
+}
+
+/*
+ * helper to find the stripe number for a given
+ * bio (before mapping).  Used to figure out which stripe has
+ * failed.  This looks up based on logical block numbers.
+ */
+static int find_logical_bio_stripe(struct btrfs_raid_bio *rbio,
+				   struct bio *bio)
+{
+	u64 logical = bio->bi_iter.bi_sector << 9;
+	int i;
+
+	for (i = 0; i < rbio->nr_data; i++) {
+		u64 stripe_start = rbio->bioc->raid_map[i];
+
+		if (in_range(logical, stripe_start, BTRFS_STRIPE_LEN))
+			return i;
+	}
+	return -1;
+}
+
+/*
+ * returns -EIO if we had too many failures
+ */
+static int fail_rbio_index(struct btrfs_raid_bio *rbio, int failed)
+{
+	unsigned long flags;
+	int ret = 0;
+
+	spin_lock_irqsave(&rbio->bio_list_lock, flags);
+
+	/* we already know this stripe is bad, move on */
+	if (rbio->faila == failed || rbio->failb == failed)
+		goto out;
+
+	if (rbio->faila == -1) {
+		/* first failure on this rbio */
+		rbio->faila = failed;
+		atomic_inc(&rbio->error);
+	} else if (rbio->failb == -1) {
+		/* second failure on this rbio */
+		rbio->failb = failed;
+		atomic_inc(&rbio->error);
+	} else {
+		ret = -EIO;
+	}
+out:
+	spin_unlock_irqrestore(&rbio->bio_list_lock, flags);
+
+	return ret;
+}
+
+/*
+ * helper to fail a stripe based on a physical disk
+ * bio.
+ */
+static int fail_bio_stripe(struct btrfs_raid_bio *rbio,
+			   struct bio *bio)
+{
+	int failed = find_bio_stripe(rbio, bio);
+
+	if (failed < 0)
+		return -EIO;
+
+	return fail_rbio_index(rbio, failed);
+}
+
+/*
+ * For subpage case, we can no longer set page Uptodate directly for
+ * stripe_pages[], thus we need to locate the sector.
+ */
+static struct sector_ptr *find_stripe_sector(struct btrfs_raid_bio *rbio,
+					     struct page *page,
+					     unsigned int pgoff)
+{
+	int i;
+
+	for (i = 0; i < rbio->nr_sectors; i++) {
+		struct sector_ptr *sector = &rbio->stripe_sectors[i];
+
+		if (sector->page == page && sector->pgoff == pgoff)
+			return sector;
+	}
+	return NULL;
+}
+
+/*
+ * this sets each page in the bio uptodate.  It should only be used on private
+ * rbio pages, nothing that comes in from the higher layers
+ */
+static void set_bio_pages_uptodate(struct btrfs_raid_bio *rbio, struct bio *bio)
+{
+	const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
+	struct bio_vec *bvec;
+	struct bvec_iter_all iter_all;
+
+	ASSERT(!bio_flagged(bio, BIO_CLONED));
+
+	bio_for_each_segment_all(bvec, bio, iter_all) {
+		struct sector_ptr *sector;
+		int pgoff;
+
+		for (pgoff = bvec->bv_offset; pgoff - bvec->bv_offset < bvec->bv_len;
+		     pgoff += sectorsize) {
+			sector = find_stripe_sector(rbio, bvec->bv_page, pgoff);
+			ASSERT(sector);
+			if (sector)
+				sector->uptodate = 1;
+		}
+	}
+}
+
+static void raid56_bio_end_io(struct bio *bio)
+{
+	struct btrfs_raid_bio *rbio = bio->bi_private;
+
+	if (bio->bi_status)
+		fail_bio_stripe(rbio, bio);
+	else
+		set_bio_pages_uptodate(rbio, bio);
+
+	bio_put(bio);
+
+	if (atomic_dec_and_test(&rbio->stripes_pending))
+		queue_work(rbio->bioc->fs_info->endio_raid56_workers,
+			   &rbio->end_io_work);
+}
+
+/*
+ * End io handler for the read phase of the RMW cycle.  All the bios here are
+ * physical stripe bios we've read from the disk so we can recalculate the
+ * parity of the stripe.
+ *
+ * This will usually kick off finish_rmw once all the bios are read in, but it
+ * may trigger parity reconstruction if we had any errors along the way
+ */
+static void raid56_rmw_end_io_work(struct work_struct *work)
+{
+	struct btrfs_raid_bio *rbio =
+		container_of(work, struct btrfs_raid_bio, end_io_work);
+
+	if (atomic_read(&rbio->error) > rbio->bioc->max_errors) {
+		rbio_orig_end_io(rbio, BLK_STS_IOERR);
+		return;
+	}
+
+	/*
+	 * This will normally call finish_rmw to start our write but if there
+	 * are any failed stripes we'll reconstruct from parity first.
+	 */
+	validate_rbio_for_rmw(rbio);
+}
+
+/*
+ * the stripe must be locked by the caller.  It will
+ * unlock after all the writes are done
+ */
+static int raid56_rmw_stripe(struct btrfs_raid_bio *rbio)
+{
+	int bios_to_read = 0;
+	struct bio_list bio_list;
+	const int nr_data_sectors = rbio->stripe_nsectors * rbio->nr_data;
+	int ret;
+	int total_sector_nr;
+	struct bio *bio;
+
+	bio_list_init(&bio_list);
+
+	ret = alloc_rbio_pages(rbio);
+	if (ret)
+		goto cleanup;
+
+	index_rbio_pages(rbio);
+
+	atomic_set(&rbio->error, 0);
+	/* Build a list of bios to read all the missing data sectors. */
+	for (total_sector_nr = 0; total_sector_nr < nr_data_sectors;
+	     total_sector_nr++) {
+		struct sector_ptr *sector;
+		int stripe = total_sector_nr / rbio->stripe_nsectors;
+		int sectornr = total_sector_nr % rbio->stripe_nsectors;
+
+		/*
+		 * We want to find all the sectors missing from the rbio and
+		 * read them from the disk.  If sector_in_rbio() finds a page
+		 * in the bio list we don't need to read it off the stripe.
+		 */
+		sector = sector_in_rbio(rbio, stripe, sectornr, 1);
+		if (sector)
+			continue;
+
+		sector = rbio_stripe_sector(rbio, stripe, sectornr);
+		/*
+		 * The bio cache may have handed us an uptodate page.  If so,
+		 * use it.
+		 */
+		if (sector->uptodate)
+			continue;
+
+		ret = rbio_add_io_sector(rbio, &bio_list, sector,
+			       stripe, sectornr, REQ_OP_READ);
+		if (ret)
+			goto cleanup;
+	}
+
+	bios_to_read = bio_list_size(&bio_list);
+	if (!bios_to_read) {
+		/*
+		 * this can happen if others have merged with
+		 * us, it means there is nothing left to read.
+		 * But if there are missing devices it may not be
+		 * safe to do the full stripe write yet.
+		 */
+		goto finish;
+	}
+
+	/*
+	 * The bioc may be freed once we submit the last bio. Make sure not to
+	 * touch it after that.
+	 */
+	atomic_set(&rbio->stripes_pending, bios_to_read);
+	INIT_WORK(&rbio->end_io_work, raid56_rmw_end_io_work);
+	while ((bio = bio_list_pop(&bio_list))) {
+		bio->bi_end_io = raid56_bio_end_io;
+
+		if (trace_raid56_read_partial_enabled()) {
+			struct raid56_bio_trace_info trace_info = { 0 };
+
+			bio_get_trace_info(rbio, bio, &trace_info);
+			trace_raid56_read_partial(rbio, bio, &trace_info);
+		}
+		submit_bio(bio);
+	}
+	/* the actual write will happen once the reads are done */
+	return 0;
+
+cleanup:
+	rbio_orig_end_io(rbio, BLK_STS_IOERR);
+
+	while ((bio = bio_list_pop(&bio_list)))
+		bio_put(bio);
+
+	return -EIO;
+
+finish:
+	validate_rbio_for_rmw(rbio);
+	return 0;
+}
+
+/*
+ * if the upper layers pass in a full stripe, we thank them by only allocating
+ * enough pages to hold the parity, and sending it all down quickly.
+ */
+static int full_stripe_write(struct btrfs_raid_bio *rbio)
+{
+	int ret;
+
+	ret = alloc_rbio_parity_pages(rbio);
+	if (ret)
+		return ret;
+
+	ret = lock_stripe_add(rbio);
+	if (ret == 0)
+		finish_rmw(rbio);
+	return 0;
+}
+
+/*
+ * partial stripe writes get handed over to async helpers.
+ * We're really hoping to merge a few more writes into this
+ * rbio before calculating new parity
+ */
+static int partial_stripe_write(struct btrfs_raid_bio *rbio)
+{
+	int ret;
+
+	ret = lock_stripe_add(rbio);
+	if (ret == 0)
+		start_async_work(rbio, rmw_work);
+	return 0;
+}
+
+/*
+ * sometimes while we were reading from the drive to
+ * recalculate parity, enough new bios come into create
+ * a full stripe.  So we do a check here to see if we can
+ * go directly to finish_rmw
+ */
+static int __raid56_parity_write(struct btrfs_raid_bio *rbio)
+{
+	/* head off into rmw land if we don't have a full stripe */
+	if (!rbio_is_full(rbio))
+		return partial_stripe_write(rbio);
+	return full_stripe_write(rbio);
+}
+
+/*
+ * We use plugging call backs to collect full stripes.
+ * Any time we get a partial stripe write while plugged
+ * we collect it into a list.  When the unplug comes down,
+ * we sort the list by logical block number and merge
+ * everything we can into the same rbios
+ */
+struct btrfs_plug_cb {
+	struct blk_plug_cb cb;
+	struct btrfs_fs_info *info;
+	struct list_head rbio_list;
+	struct work_struct work;
+};
+
+/*
+ * rbios on the plug list are sorted for easier merging.
+ */
+static int plug_cmp(void *priv, const struct list_head *a,
+		    const struct list_head *b)
+{
+	const struct btrfs_raid_bio *ra = container_of(a, struct btrfs_raid_bio,
+						       plug_list);
+	const struct btrfs_raid_bio *rb = container_of(b, struct btrfs_raid_bio,
+						       plug_list);
+	u64 a_sector = ra->bio_list.head->bi_iter.bi_sector;
+	u64 b_sector = rb->bio_list.head->bi_iter.bi_sector;
+
+	if (a_sector < b_sector)
+		return -1;
+	if (a_sector > b_sector)
+		return 1;
+	return 0;
+}
+
+static void run_plug(struct btrfs_plug_cb *plug)
+{
+	struct btrfs_raid_bio *cur;
+	struct btrfs_raid_bio *last = NULL;
+
+	/*
+	 * sort our plug list then try to merge
+	 * everything we can in hopes of creating full
+	 * stripes.
+	 */
+	list_sort(NULL, &plug->rbio_list, plug_cmp);
+	while (!list_empty(&plug->rbio_list)) {
+		cur = list_entry(plug->rbio_list.next,
+				 struct btrfs_raid_bio, plug_list);
+		list_del_init(&cur->plug_list);
+
+		if (rbio_is_full(cur)) {
+			int ret;
+
+			/* we have a full stripe, send it down */
+			ret = full_stripe_write(cur);
+			BUG_ON(ret);
+			continue;
+		}
+		if (last) {
+			if (rbio_can_merge(last, cur)) {
+				merge_rbio(last, cur);
+				__free_raid_bio(cur);
+				continue;
+
+			}
+			__raid56_parity_write(last);
+		}
+		last = cur;
+	}
+	if (last) {
+		__raid56_parity_write(last);
+	}
+	kfree(plug);
+}
+
+/*
+ * if the unplug comes from schedule, we have to push the
+ * work off to a helper thread
+ */
+static void unplug_work(struct work_struct *work)
+{
+	struct btrfs_plug_cb *plug;
+	plug = container_of(work, struct btrfs_plug_cb, work);
+	run_plug(plug);
+}
+
+static void btrfs_raid_unplug(struct blk_plug_cb *cb, bool from_schedule)
+{
+	struct btrfs_plug_cb *plug;
+	plug = container_of(cb, struct btrfs_plug_cb, cb);
+
+	if (from_schedule) {
+		INIT_WORK(&plug->work, unplug_work);
+		queue_work(plug->info->rmw_workers, &plug->work);
+		return;
+	}
+	run_plug(plug);
+}
+
+/* Add the original bio into rbio->bio_list, and update rbio::dbitmap. */
+static void rbio_add_bio(struct btrfs_raid_bio *rbio, struct bio *orig_bio)
+{
+	const struct btrfs_fs_info *fs_info = rbio->bioc->fs_info;
+	const u64 orig_logical = orig_bio->bi_iter.bi_sector << SECTOR_SHIFT;
+	const u64 full_stripe_start = rbio->bioc->raid_map[0];
+	const u32 orig_len = orig_bio->bi_iter.bi_size;
+	const u32 sectorsize = fs_info->sectorsize;
+	u64 cur_logical;
+
+	ASSERT(orig_logical >= full_stripe_start &&
+	       orig_logical + orig_len <= full_stripe_start +
+	       rbio->nr_data * BTRFS_STRIPE_LEN);
+
+	bio_list_add(&rbio->bio_list, orig_bio);
+	rbio->bio_list_bytes += orig_bio->bi_iter.bi_size;
+
+	/* Update the dbitmap. */
+	for (cur_logical = orig_logical; cur_logical < orig_logical + orig_len;
+	     cur_logical += sectorsize) {
+		int bit = ((u32)(cur_logical - full_stripe_start) >>
+			   fs_info->sectorsize_bits) % rbio->stripe_nsectors;
+
+		set_bit(bit, &rbio->dbitmap);
+	}
+}
+
+/*
+ * our main entry point for writes from the rest of the FS.
+ */
+void raid56_parity_write(struct bio *bio, struct btrfs_io_context *bioc)
+{
+	struct btrfs_fs_info *fs_info = bioc->fs_info;
+	struct btrfs_raid_bio *rbio;
+	struct btrfs_plug_cb *plug = NULL;
+	struct blk_plug_cb *cb;
+	int ret = 0;
+
+	rbio = alloc_rbio(fs_info, bioc);
+	if (IS_ERR(rbio)) {
+		ret = PTR_ERR(rbio);
+		goto fail;
+	}
+	rbio->operation = BTRFS_RBIO_WRITE;
+	rbio_add_bio(rbio, bio);
+
+	/*
+	 * don't plug on full rbios, just get them out the door
+	 * as quickly as we can
+	 */
+	if (rbio_is_full(rbio)) {
+		ret = full_stripe_write(rbio);
+		if (ret) {
+			__free_raid_bio(rbio);
+			goto fail;
+		}
+		return;
+	}
+
+	cb = blk_check_plugged(btrfs_raid_unplug, fs_info, sizeof(*plug));
+	if (cb) {
+		plug = container_of(cb, struct btrfs_plug_cb, cb);
+		if (!plug->info) {
+			plug->info = fs_info;
+			INIT_LIST_HEAD(&plug->rbio_list);
+		}
+		list_add_tail(&rbio->plug_list, &plug->rbio_list);
+	} else {
+		ret = __raid56_parity_write(rbio);
+		if (ret) {
+			__free_raid_bio(rbio);
+			goto fail;
+		}
+	}
+
+	return;
+
+fail:
+	bio->bi_status = errno_to_blk_status(ret);
+	bio_endio(bio);
+}
+
+/*
+ * all parity reconstruction happens here.  We've read in everything
+ * we can find from the drives and this does the heavy lifting of
+ * sorting the good from the bad.
+ */
+static void __raid_recover_end_io(struct btrfs_raid_bio *rbio)
+{
+	const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
+	int sectornr, stripe;
+	void **pointers;
+	void **unmap_array;
+	int faila = -1, failb = -1;
+	blk_status_t err;
+	int i;
+
+	/*
+	 * This array stores the pointer for each sector, thus it has the extra
+	 * pgoff value added from each sector
+	 */
+	pointers = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
+	if (!pointers) {
+		err = BLK_STS_RESOURCE;
+		goto cleanup_io;
+	}
+
+	/*
+	 * Store copy of pointers that does not get reordered during
+	 * reconstruction so that kunmap_local works.
+	 */
+	unmap_array = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
+	if (!unmap_array) {
+		err = BLK_STS_RESOURCE;
+		goto cleanup_pointers;
+	}
+
+	faila = rbio->faila;
+	failb = rbio->failb;
+
+	if (rbio->operation == BTRFS_RBIO_READ_REBUILD ||
+	    rbio->operation == BTRFS_RBIO_REBUILD_MISSING) {
+		spin_lock_irq(&rbio->bio_list_lock);
+		set_bit(RBIO_RMW_LOCKED_BIT, &rbio->flags);
+		spin_unlock_irq(&rbio->bio_list_lock);
+	}
+
+	index_rbio_pages(rbio);
+
+	for (sectornr = 0; sectornr < rbio->stripe_nsectors; sectornr++) {
+		struct sector_ptr *sector;
+
+		/*
+		 * Now we just use bitmap to mark the horizontal stripes in
+		 * which we have data when doing parity scrub.
+		 */
+		if (rbio->operation == BTRFS_RBIO_PARITY_SCRUB &&
+		    !test_bit(sectornr, &rbio->dbitmap))
+			continue;
+
+		/*
+		 * Setup our array of pointers with sectors from each stripe
+		 *
+		 * NOTE: store a duplicate array of pointers to preserve the
+		 * pointer order
+		 */
+		for (stripe = 0; stripe < rbio->real_stripes; stripe++) {
+			/*
+			 * If we're rebuilding a read, we have to use
+			 * pages from the bio list
+			 */
+			if ((rbio->operation == BTRFS_RBIO_READ_REBUILD ||
+			     rbio->operation == BTRFS_RBIO_REBUILD_MISSING) &&
+			    (stripe == faila || stripe == failb)) {
+				sector = sector_in_rbio(rbio, stripe, sectornr, 0);
+			} else {
+				sector = rbio_stripe_sector(rbio, stripe, sectornr);
+			}
+			ASSERT(sector->page);
+			pointers[stripe] = kmap_local_page(sector->page) +
+					   sector->pgoff;
+			unmap_array[stripe] = pointers[stripe];
+		}
+
+		/* All raid6 handling here */
+		if (rbio->bioc->map_type & BTRFS_BLOCK_GROUP_RAID6) {
+			/* Single failure, rebuild from parity raid5 style */
+			if (failb < 0) {
+				if (faila == rbio->nr_data) {
+					/*
+					 * Just the P stripe has failed, without
+					 * a bad data or Q stripe.
+					 * TODO, we should redo the xor here.
+					 */
+					err = BLK_STS_IOERR;
+					goto cleanup;
+				}
+				/*
+				 * a single failure in raid6 is rebuilt
+				 * in the pstripe code below
+				 */
+				goto pstripe;
+			}
+
+			/* make sure our ps and qs are in order */
+			if (faila > failb)
+				swap(faila, failb);
+
+			/* if the q stripe is failed, do a pstripe reconstruction
+			 * from the xors.
+			 * If both the q stripe and the P stripe are failed, we're
+			 * here due to a crc mismatch and we can't give them the
+			 * data they want
+			 */
+			if (rbio->bioc->raid_map[failb] == RAID6_Q_STRIPE) {
+				if (rbio->bioc->raid_map[faila] ==
+				    RAID5_P_STRIPE) {
+					err = BLK_STS_IOERR;
+					goto cleanup;
+				}
+				/*
+				 * otherwise we have one bad data stripe and
+				 * a good P stripe.  raid5!
+				 */
+				goto pstripe;
+			}
+
+			if (rbio->bioc->raid_map[failb] == RAID5_P_STRIPE) {
+				raid6_datap_recov(rbio->real_stripes,
+						  sectorsize, faila, pointers);
+			} else {
+				raid6_2data_recov(rbio->real_stripes,
+						  sectorsize, faila, failb,
+						  pointers);
+			}
+		} else {
+			void *p;
+
+			/* rebuild from P stripe here (raid5 or raid6) */
+			BUG_ON(failb != -1);
+pstripe:
+			/* Copy parity block into failed block to start with */
+			memcpy(pointers[faila], pointers[rbio->nr_data], sectorsize);
+
+			/* rearrange the pointer array */
+			p = pointers[faila];
+			for (stripe = faila; stripe < rbio->nr_data - 1; stripe++)
+				pointers[stripe] = pointers[stripe + 1];
+			pointers[rbio->nr_data - 1] = p;
+
+			/* xor in the rest */
+			run_xor(pointers, rbio->nr_data - 1, sectorsize);
+		}
+		/* if we're doing this rebuild as part of an rmw, go through
+		 * and set all of our private rbio pages in the
+		 * failed stripes as uptodate.  This way finish_rmw will
+		 * know they can be trusted.  If this was a read reconstruction,
+		 * other endio functions will fiddle the uptodate bits
+		 */
+		if (rbio->operation == BTRFS_RBIO_WRITE) {
+			for (i = 0;  i < rbio->stripe_nsectors; i++) {
+				if (faila != -1) {
+					sector = rbio_stripe_sector(rbio, faila, i);
+					sector->uptodate = 1;
+				}
+				if (failb != -1) {
+					sector = rbio_stripe_sector(rbio, failb, i);
+					sector->uptodate = 1;
+				}
+			}
+		}
+		for (stripe = rbio->real_stripes - 1; stripe >= 0; stripe--)
+			kunmap_local(unmap_array[stripe]);
+	}
+
+	err = BLK_STS_OK;
+cleanup:
+	kfree(unmap_array);
+cleanup_pointers:
+	kfree(pointers);
+
+cleanup_io:
+	/*
+	 * Similar to READ_REBUILD, REBUILD_MISSING at this point also has a
+	 * valid rbio which is consistent with ondisk content, thus such a
+	 * valid rbio can be cached to avoid further disk reads.
+	 */
+	if (rbio->operation == BTRFS_RBIO_READ_REBUILD ||
+	    rbio->operation == BTRFS_RBIO_REBUILD_MISSING) {
+		/*
+		 * - In case of two failures, where rbio->failb != -1:
+		 *
+		 *   Do not cache this rbio since the above read reconstruction
+		 *   (raid6_datap_recov() or raid6_2data_recov()) may have
+		 *   changed some content of stripes which are not identical to
+		 *   on-disk content any more, otherwise, a later write/recover
+		 *   may steal stripe_pages from this rbio and end up with
+		 *   corruptions or rebuild failures.
+		 *
+		 * - In case of single failure, where rbio->failb == -1:
+		 *
+		 *   Cache this rbio iff the above read reconstruction is
+		 *   executed without problems.
+		 */
+		if (err == BLK_STS_OK && rbio->failb < 0)
+			cache_rbio_pages(rbio);
+		else
+			clear_bit(RBIO_CACHE_READY_BIT, &rbio->flags);
+
+		rbio_orig_end_io(rbio, err);
+	} else if (err == BLK_STS_OK) {
+		rbio->faila = -1;
+		rbio->failb = -1;
+
+		if (rbio->operation == BTRFS_RBIO_WRITE)
+			finish_rmw(rbio);
+		else if (rbio->operation == BTRFS_RBIO_PARITY_SCRUB)
+			finish_parity_scrub(rbio, 0);
+		else
+			BUG();
+	} else {
+		rbio_orig_end_io(rbio, err);
+	}
+}
+
+/*
+ * This is called only for stripes we've read from disk to reconstruct the
+ * parity.
+ */
+static void raid_recover_end_io_work(struct work_struct *work)
+{
+	struct btrfs_raid_bio *rbio =
+		container_of(work, struct btrfs_raid_bio, end_io_work);
+
+	if (atomic_read(&rbio->error) > rbio->bioc->max_errors)
+		rbio_orig_end_io(rbio, BLK_STS_IOERR);
+	else
+		__raid_recover_end_io(rbio);
+}
+
+/*
+ * reads everything we need off the disk to reconstruct
+ * the parity. endio handlers trigger final reconstruction
+ * when the IO is done.
+ *
+ * This is used both for reads from the higher layers and for
+ * parity construction required to finish a rmw cycle.
+ */
+static int __raid56_parity_recover(struct btrfs_raid_bio *rbio)
+{
+	int bios_to_read = 0;
+	struct bio_list bio_list;
+	int ret;
+	int total_sector_nr;
+	struct bio *bio;
+
+	bio_list_init(&bio_list);
+
+	ret = alloc_rbio_pages(rbio);
+	if (ret)
+		goto cleanup;
+
+	atomic_set(&rbio->error, 0);
+
+	/*
+	 * Read everything that hasn't failed. However this time we will
+	 * not trust any cached sector.
+	 * As we may read out some stale data but higher layer is not reading
+	 * that stale part.
+	 *
+	 * So here we always re-read everything in recovery path.
+	 */
+	for (total_sector_nr = 0; total_sector_nr < rbio->nr_sectors;
+	     total_sector_nr++) {
+		int stripe = total_sector_nr / rbio->stripe_nsectors;
+		int sectornr = total_sector_nr % rbio->stripe_nsectors;
+		struct sector_ptr *sector;
+
+		if (rbio->faila == stripe || rbio->failb == stripe) {
+			atomic_inc(&rbio->error);
+			/* Skip the current stripe. */
+			ASSERT(sectornr == 0);
+			total_sector_nr += rbio->stripe_nsectors - 1;
+			continue;
+		}
+		sector = rbio_stripe_sector(rbio, stripe, sectornr);
+		ret = rbio_add_io_sector(rbio, &bio_list, sector, stripe,
+					 sectornr, REQ_OP_READ);
+		if (ret < 0)
+			goto cleanup;
+	}
+
+	bios_to_read = bio_list_size(&bio_list);
+	if (!bios_to_read) {
+		/*
+		 * we might have no bios to read just because the pages
+		 * were up to date, or we might have no bios to read because
+		 * the devices were gone.
+		 */
+		if (atomic_read(&rbio->error) <= rbio->bioc->max_errors) {
+			__raid_recover_end_io(rbio);
+			return 0;
+		} else {
+			goto cleanup;
+		}
+	}
+
+	/*
+	 * The bioc may be freed once we submit the last bio. Make sure not to
+	 * touch it after that.
+	 */
+	atomic_set(&rbio->stripes_pending, bios_to_read);
+	INIT_WORK(&rbio->end_io_work, raid_recover_end_io_work);
+	while ((bio = bio_list_pop(&bio_list))) {
+		bio->bi_end_io = raid56_bio_end_io;
+
+		if (trace_raid56_scrub_read_recover_enabled()) {
+			struct raid56_bio_trace_info trace_info = { 0 };
+
+			bio_get_trace_info(rbio, bio, &trace_info);
+			trace_raid56_scrub_read_recover(rbio, bio, &trace_info);
+		}
+		submit_bio(bio);
+	}
+
+	return 0;
+
+cleanup:
+	if (rbio->operation == BTRFS_RBIO_READ_REBUILD ||
+	    rbio->operation == BTRFS_RBIO_REBUILD_MISSING)
+		rbio_orig_end_io(rbio, BLK_STS_IOERR);
+
+	while ((bio = bio_list_pop(&bio_list)))
+		bio_put(bio);
+
+	return -EIO;
+}
+
+/*
+ * the main entry point for reads from the higher layers.  This
+ * is really only called when the normal read path had a failure,
+ * so we assume the bio they send down corresponds to a failed part
+ * of the drive.
+ */
+void raid56_parity_recover(struct bio *bio, struct btrfs_io_context *bioc,
+			   int mirror_num)
+{
+	struct btrfs_fs_info *fs_info = bioc->fs_info;
+	struct btrfs_raid_bio *rbio;
+
+	rbio = alloc_rbio(fs_info, bioc);
+	if (IS_ERR(rbio)) {
+		bio->bi_status = errno_to_blk_status(PTR_ERR(rbio));
+		goto out_end_bio;
+	}
+
+	rbio->operation = BTRFS_RBIO_READ_REBUILD;
+	rbio_add_bio(rbio, bio);
+
+	rbio->faila = find_logical_bio_stripe(rbio, bio);
+	if (rbio->faila == -1) {
+		btrfs_warn(fs_info,
+"%s could not find the bad stripe in raid56 so that we cannot recover any more (bio has logical %llu len %llu, bioc has map_type %llu)",
+			   __func__, bio->bi_iter.bi_sector << 9,
+			   (u64)bio->bi_iter.bi_size, bioc->map_type);
+		__free_raid_bio(rbio);
+		bio->bi_status = BLK_STS_IOERR;
+		goto out_end_bio;
+	}
+
+	/*
+	 * Loop retry:
+	 * for 'mirror == 2', reconstruct from all other stripes.
+	 * for 'mirror_num > 2', select a stripe to fail on every retry.
+	 */
+	if (mirror_num > 2) {
+		/*
+		 * 'mirror == 3' is to fail the p stripe and
+		 * reconstruct from the q stripe.  'mirror > 3' is to
+		 * fail a data stripe and reconstruct from p+q stripe.
+		 */
+		rbio->failb = rbio->real_stripes - (mirror_num - 1);
+		ASSERT(rbio->failb > 0);
+		if (rbio->failb <= rbio->faila)
+			rbio->failb--;
+	}
+
+	if (lock_stripe_add(rbio))
+		return;
+
+	/*
+	 * This adds our rbio to the list of rbios that will be handled after
+	 * the current lock owner is done.
+	 */
+	__raid56_parity_recover(rbio);
+	return;
+
+out_end_bio:
+	bio_endio(bio);
+}
+
+static void rmw_work(struct work_struct *work)
+{
+	struct btrfs_raid_bio *rbio;
+
+	rbio = container_of(work, struct btrfs_raid_bio, work);
+	raid56_rmw_stripe(rbio);
+}
+
+static void read_rebuild_work(struct work_struct *work)
+{
+	struct btrfs_raid_bio *rbio;
+
+	rbio = container_of(work, struct btrfs_raid_bio, work);
+	__raid56_parity_recover(rbio);
+}
+
+/*
+ * The following code is used to scrub/replace the parity stripe
+ *
+ * Caller must have already increased bio_counter for getting @bioc.
+ *
+ * Note: We need make sure all the pages that add into the scrub/replace
+ * raid bio are correct and not be changed during the scrub/replace. That
+ * is those pages just hold metadata or file data with checksum.
+ */
+
+struct btrfs_raid_bio *raid56_parity_alloc_scrub_rbio(struct bio *bio,
+				struct btrfs_io_context *bioc,
+				struct btrfs_device *scrub_dev,
+				unsigned long *dbitmap, int stripe_nsectors)
+{
+	struct btrfs_fs_info *fs_info = bioc->fs_info;
+	struct btrfs_raid_bio *rbio;
+	int i;
+
+	rbio = alloc_rbio(fs_info, bioc);
+	if (IS_ERR(rbio))
+		return NULL;
+	bio_list_add(&rbio->bio_list, bio);
+	/*
+	 * This is a special bio which is used to hold the completion handler
+	 * and make the scrub rbio is similar to the other types
+	 */
+	ASSERT(!bio->bi_iter.bi_size);
+	rbio->operation = BTRFS_RBIO_PARITY_SCRUB;
+
+	/*
+	 * After mapping bioc with BTRFS_MAP_WRITE, parities have been sorted
+	 * to the end position, so this search can start from the first parity
+	 * stripe.
+	 */
+	for (i = rbio->nr_data; i < rbio->real_stripes; i++) {
+		if (bioc->stripes[i].dev == scrub_dev) {
+			rbio->scrubp = i;
+			break;
+		}
+	}
+	ASSERT(i < rbio->real_stripes);
+
+	bitmap_copy(&rbio->dbitmap, dbitmap, stripe_nsectors);
+	return rbio;
+}
+
+/* Used for both parity scrub and missing. */
+void raid56_add_scrub_pages(struct btrfs_raid_bio *rbio, struct page *page,
+			    unsigned int pgoff, u64 logical)
+{
+	const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
+	int stripe_offset;
+	int index;
+
+	ASSERT(logical >= rbio->bioc->raid_map[0]);
+	ASSERT(logical + sectorsize <= rbio->bioc->raid_map[0] +
+				       BTRFS_STRIPE_LEN * rbio->nr_data);
+	stripe_offset = (int)(logical - rbio->bioc->raid_map[0]);
+	index = stripe_offset / sectorsize;
+	rbio->bio_sectors[index].page = page;
+	rbio->bio_sectors[index].pgoff = pgoff;
+}
+
+/*
+ * We just scrub the parity that we have correct data on the same horizontal,
+ * so we needn't allocate all pages for all the stripes.
+ */
+static int alloc_rbio_essential_pages(struct btrfs_raid_bio *rbio)
+{
+	const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
+	int total_sector_nr;
+
+	for (total_sector_nr = 0; total_sector_nr < rbio->nr_sectors;
+	     total_sector_nr++) {
+		struct page *page;
+		int sectornr = total_sector_nr % rbio->stripe_nsectors;
+		int index = (total_sector_nr * sectorsize) >> PAGE_SHIFT;
+
+		if (!test_bit(sectornr, &rbio->dbitmap))
+			continue;
+		if (rbio->stripe_pages[index])
+			continue;
+		page = alloc_page(GFP_NOFS);
+		if (!page)
+			return -ENOMEM;
+		rbio->stripe_pages[index] = page;
+	}
+	index_stripe_sectors(rbio);
+	return 0;
+}
+
+static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
+					 int need_check)
+{
+	struct btrfs_io_context *bioc = rbio->bioc;
+	const u32 sectorsize = bioc->fs_info->sectorsize;
+	void **pointers = rbio->finish_pointers;
+	unsigned long *pbitmap = &rbio->finish_pbitmap;
+	int nr_data = rbio->nr_data;
+	int stripe;
+	int sectornr;
+	bool has_qstripe;
+	struct sector_ptr p_sector = { 0 };
+	struct sector_ptr q_sector = { 0 };
+	struct bio_list bio_list;
+	struct bio *bio;
+	int is_replace = 0;
+	int ret;
+
+	bio_list_init(&bio_list);
+
+	if (rbio->real_stripes - rbio->nr_data == 1)
+		has_qstripe = false;
+	else if (rbio->real_stripes - rbio->nr_data == 2)
+		has_qstripe = true;
+	else
+		BUG();
+
+	if (bioc->num_tgtdevs && bioc->tgtdev_map[rbio->scrubp]) {
+		is_replace = 1;
+		bitmap_copy(pbitmap, &rbio->dbitmap, rbio->stripe_nsectors);
+	}
+
+	/*
+	 * Because the higher layers(scrubber) are unlikely to
+	 * use this area of the disk again soon, so don't cache
+	 * it.
+	 */
+	clear_bit(RBIO_CACHE_READY_BIT, &rbio->flags);
+
+	if (!need_check)
+		goto writeback;
+
+	p_sector.page = alloc_page(GFP_NOFS);
+	if (!p_sector.page)
+		goto cleanup;
+	p_sector.pgoff = 0;
+	p_sector.uptodate = 1;
+
+	if (has_qstripe) {
+		/* RAID6, allocate and map temp space for the Q stripe */
+		q_sector.page = alloc_page(GFP_NOFS);
+		if (!q_sector.page) {
+			__free_page(p_sector.page);
+			p_sector.page = NULL;
+			goto cleanup;
+		}
+		q_sector.pgoff = 0;
+		q_sector.uptodate = 1;
+		pointers[rbio->real_stripes - 1] = kmap_local_page(q_sector.page);
+	}
+
+	atomic_set(&rbio->error, 0);
+
+	/* Map the parity stripe just once */
+	pointers[nr_data] = kmap_local_page(p_sector.page);
+
+	for_each_set_bit(sectornr, &rbio->dbitmap, rbio->stripe_nsectors) {
+		struct sector_ptr *sector;
+		void *parity;
+
+		/* first collect one page from each data stripe */
+		for (stripe = 0; stripe < nr_data; stripe++) {
+			sector = sector_in_rbio(rbio, stripe, sectornr, 0);
+			pointers[stripe] = kmap_local_page(sector->page) +
+					   sector->pgoff;
+		}
+
+		if (has_qstripe) {
+			/* RAID6, call the library function to fill in our P/Q */
+			raid6_call.gen_syndrome(rbio->real_stripes, sectorsize,
+						pointers);
+		} else {
+			/* raid5 */
+			memcpy(pointers[nr_data], pointers[0], sectorsize);
+			run_xor(pointers + 1, nr_data - 1, sectorsize);
+		}
+
+		/* Check scrubbing parity and repair it */
+		sector = rbio_stripe_sector(rbio, rbio->scrubp, sectornr);
+		parity = kmap_local_page(sector->page) + sector->pgoff;
+		if (memcmp(parity, pointers[rbio->scrubp], sectorsize) != 0)
+			memcpy(parity, pointers[rbio->scrubp], sectorsize);
+		else
+			/* Parity is right, needn't writeback */
+			bitmap_clear(&rbio->dbitmap, sectornr, 1);
+		kunmap_local(parity);
+
+		for (stripe = nr_data - 1; stripe >= 0; stripe--)
+			kunmap_local(pointers[stripe]);
+	}
+
+	kunmap_local(pointers[nr_data]);
+	__free_page(p_sector.page);
+	p_sector.page = NULL;
+	if (q_sector.page) {
+		kunmap_local(pointers[rbio->real_stripes - 1]);
+		__free_page(q_sector.page);
+		q_sector.page = NULL;
+	}
+
+writeback:
+	/*
+	 * time to start writing.  Make bios for everything from the
+	 * higher layers (the bio_list in our rbio) and our p/q.  Ignore
+	 * everything else.
+	 */
+	for_each_set_bit(sectornr, &rbio->dbitmap, rbio->stripe_nsectors) {
+		struct sector_ptr *sector;
+
+		sector = rbio_stripe_sector(rbio, rbio->scrubp, sectornr);
+		ret = rbio_add_io_sector(rbio, &bio_list, sector, rbio->scrubp,
+					 sectornr, REQ_OP_WRITE);
+		if (ret)
+			goto cleanup;
+	}
+
+	if (!is_replace)
+		goto submit_write;
+
+	for_each_set_bit(sectornr, pbitmap, rbio->stripe_nsectors) {
+		struct sector_ptr *sector;
+
+		sector = rbio_stripe_sector(rbio, rbio->scrubp, sectornr);
+		ret = rbio_add_io_sector(rbio, &bio_list, sector,
+				       bioc->tgtdev_map[rbio->scrubp],
+				       sectornr, REQ_OP_WRITE);
+		if (ret)
+			goto cleanup;
+	}
+
+submit_write:
+	nr_data = bio_list_size(&bio_list);
+	if (!nr_data) {
+		/* Every parity is right */
+		rbio_orig_end_io(rbio, BLK_STS_OK);
+		return;
+	}
+
+	atomic_set(&rbio->stripes_pending, nr_data);
+
+	while ((bio = bio_list_pop(&bio_list))) {
+		bio->bi_end_io = raid_write_end_io;
+
+		if (trace_raid56_scrub_write_stripe_enabled()) {
+			struct raid56_bio_trace_info trace_info = { 0 };
+
+			bio_get_trace_info(rbio, bio, &trace_info);
+			trace_raid56_scrub_write_stripe(rbio, bio, &trace_info);
+		}
+		submit_bio(bio);
+	}
+	return;
+
+cleanup:
+	rbio_orig_end_io(rbio, BLK_STS_IOERR);
+
+	while ((bio = bio_list_pop(&bio_list)))
+		bio_put(bio);
+}
+
+static inline int is_data_stripe(struct btrfs_raid_bio *rbio, int stripe)
+{
+	if (stripe >= 0 && stripe < rbio->nr_data)
+		return 1;
+	return 0;
+}
+
+/*
+ * While we're doing the parity check and repair, we could have errors
+ * in reading pages off the disk.  This checks for errors and if we're
+ * not able to read the page it'll trigger parity reconstruction.  The
+ * parity scrub will be finished after we've reconstructed the failed
+ * stripes
+ */
+static void validate_rbio_for_parity_scrub(struct btrfs_raid_bio *rbio)
+{
+	if (atomic_read(&rbio->error) > rbio->bioc->max_errors)
+		goto cleanup;
+
+	if (rbio->faila >= 0 || rbio->failb >= 0) {
+		int dfail = 0, failp = -1;
+
+		if (is_data_stripe(rbio, rbio->faila))
+			dfail++;
+		else if (is_parity_stripe(rbio->faila))
+			failp = rbio->faila;
+
+		if (is_data_stripe(rbio, rbio->failb))
+			dfail++;
+		else if (is_parity_stripe(rbio->failb))
+			failp = rbio->failb;
+
+		/*
+		 * Because we can not use a scrubbing parity to repair
+		 * the data, so the capability of the repair is declined.
+		 * (In the case of RAID5, we can not repair anything)
+		 */
+		if (dfail > rbio->bioc->max_errors - 1)
+			goto cleanup;
+
+		/*
+		 * If all data is good, only parity is correctly, just
+		 * repair the parity.
+		 */
+		if (dfail == 0) {
+			finish_parity_scrub(rbio, 0);
+			return;
+		}
+
+		/*
+		 * Here means we got one corrupted data stripe and one
+		 * corrupted parity on RAID6, if the corrupted parity
+		 * is scrubbing parity, luckily, use the other one to repair
+		 * the data, or we can not repair the data stripe.
+		 */
+		if (failp != rbio->scrubp)
+			goto cleanup;
+
+		__raid_recover_end_io(rbio);
+	} else {
+		finish_parity_scrub(rbio, 1);
+	}
+	return;
+
+cleanup:
+	rbio_orig_end_io(rbio, BLK_STS_IOERR);
+}
+
+/*
+ * end io for the read phase of the rmw cycle.  All the bios here are physical
+ * stripe bios we've read from the disk so we can recalculate the parity of the
+ * stripe.
+ *
+ * This will usually kick off finish_rmw once all the bios are read in, but it
+ * may trigger parity reconstruction if we had any errors along the way
+ */
+static void raid56_parity_scrub_end_io_work(struct work_struct *work)
+{
+	struct btrfs_raid_bio *rbio =
+		container_of(work, struct btrfs_raid_bio, end_io_work);
+
+	/*
+	 * This will normally call finish_rmw to start our write, but if there
+	 * are any failed stripes we'll reconstruct from parity first
+	 */
+	validate_rbio_for_parity_scrub(rbio);
+}
+
+static void raid56_parity_scrub_stripe(struct btrfs_raid_bio *rbio)
+{
+	int bios_to_read = 0;
+	struct bio_list bio_list;
+	int ret;
+	int total_sector_nr;
+	struct bio *bio;
+
+	bio_list_init(&bio_list);
+
+	ret = alloc_rbio_essential_pages(rbio);
+	if (ret)
+		goto cleanup;
+
+	atomic_set(&rbio->error, 0);
+	/* Build a list of bios to read all the missing parts. */
+	for (total_sector_nr = 0; total_sector_nr < rbio->nr_sectors;
+	     total_sector_nr++) {
+		int sectornr = total_sector_nr % rbio->stripe_nsectors;
+		int stripe = total_sector_nr / rbio->stripe_nsectors;
+		struct sector_ptr *sector;
+
+		/* No data in the vertical stripe, no need to read. */
+		if (!test_bit(sectornr, &rbio->dbitmap))
+			continue;
+
+		/*
+		 * We want to find all the sectors missing from the rbio and
+		 * read them from the disk. If sector_in_rbio() finds a sector
+		 * in the bio list we don't need to read it off the stripe.
+		 */
+		sector = sector_in_rbio(rbio, stripe, sectornr, 1);
+		if (sector)
+			continue;
+
+		sector = rbio_stripe_sector(rbio, stripe, sectornr);
+		/*
+		 * The bio cache may have handed us an uptodate sector.  If so,
+		 * use it.
+		 */
+		if (sector->uptodate)
+			continue;
+
+		ret = rbio_add_io_sector(rbio, &bio_list, sector, stripe,
+					 sectornr, REQ_OP_READ);
+		if (ret)
+			goto cleanup;
+	}
+
+	bios_to_read = bio_list_size(&bio_list);
+	if (!bios_to_read) {
+		/*
+		 * this can happen if others have merged with
+		 * us, it means there is nothing left to read.
+		 * But if there are missing devices it may not be
+		 * safe to do the full stripe write yet.
+		 */
+		goto finish;
+	}
+
+	/*
+	 * The bioc may be freed once we submit the last bio. Make sure not to
+	 * touch it after that.
+	 */
+	atomic_set(&rbio->stripes_pending, bios_to_read);
+	INIT_WORK(&rbio->end_io_work, raid56_parity_scrub_end_io_work);
+	while ((bio = bio_list_pop(&bio_list))) {
+		bio->bi_end_io = raid56_bio_end_io;
+
+		if (trace_raid56_scrub_read_enabled()) {
+			struct raid56_bio_trace_info trace_info = { 0 };
+
+			bio_get_trace_info(rbio, bio, &trace_info);
+			trace_raid56_scrub_read(rbio, bio, &trace_info);
+		}
+		submit_bio(bio);
+	}
+	/* the actual write will happen once the reads are done */
+	return;
+
+cleanup:
+	rbio_orig_end_io(rbio, BLK_STS_IOERR);
+
+	while ((bio = bio_list_pop(&bio_list)))
+		bio_put(bio);
+
+	return;
+
+finish:
+	validate_rbio_for_parity_scrub(rbio);
+}
+
+static void scrub_parity_work(struct work_struct *work)
+{
+	struct btrfs_raid_bio *rbio;
+
+	rbio = container_of(work, struct btrfs_raid_bio, work);
+	raid56_parity_scrub_stripe(rbio);
+}
+
+void raid56_parity_submit_scrub_rbio(struct btrfs_raid_bio *rbio)
+{
+	if (!lock_stripe_add(rbio))
+		start_async_work(rbio, scrub_parity_work);
+}
+
+/* The following code is used for dev replace of a missing RAID 5/6 device. */
+
+struct btrfs_raid_bio *
+raid56_alloc_missing_rbio(struct bio *bio, struct btrfs_io_context *bioc)
+{
+	struct btrfs_fs_info *fs_info = bioc->fs_info;
+	struct btrfs_raid_bio *rbio;
+
+	rbio = alloc_rbio(fs_info, bioc);
+	if (IS_ERR(rbio))
+		return NULL;
+
+	rbio->operation = BTRFS_RBIO_REBUILD_MISSING;
+	bio_list_add(&rbio->bio_list, bio);
+	/*
+	 * This is a special bio which is used to hold the completion handler
+	 * and make the scrub rbio is similar to the other types
+	 */
+	ASSERT(!bio->bi_iter.bi_size);
+
+	rbio->faila = find_logical_bio_stripe(rbio, bio);
+	if (rbio->faila == -1) {
+		btrfs_warn_rl(fs_info,
+	"can not determine the failed stripe number for full stripe %llu",
+			      bioc->raid_map[0]);
+		__free_raid_bio(rbio);
+		return NULL;
+	}
+
+	return rbio;
+}
+
+void raid56_submit_missing_rbio(struct btrfs_raid_bio *rbio)
+{
+	if (!lock_stripe_add(rbio))
+		start_async_work(rbio, read_rebuild_work);
+}