1 files changed, 30 insertions, 9 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index d04c82c88418..18d384f4af54 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -985,6 +985,7 @@ static noinline int cow_file_range(struct inode *inode,
 	u64 num_bytes;
 	unsigned long ram_size;
 	u64 cur_alloc_size = 0;
+	u64 min_alloc_size;
 	u64 blocksize = fs_info->sectorsize;
 	struct btrfs_key ins;
 	struct extent_map *em;
@@ -1035,10 +1036,26 @@ static noinline int cow_file_range(struct inode *inode,
 	btrfs_drop_extent_cache(BTRFS_I(inode), start,
 			start + num_bytes - 1, 0);
 
+	/*
+	 * Relocation relies on the relocated extents to have exactly the same
+	 * size as the original extents. Normally writeback for relocation data
+	 * extents follows a NOCOW path because relocation preallocates the
+	 * extents. However, due to an operation such as scrub turning a block
+	 * group to RO mode, it may fallback to COW mode, so we must make sure
+	 * an extent allocated during COW has exactly the requested size and can
+	 * not be split into smaller extents, otherwise relocation breaks and
+	 * fails during the stage where it updates the bytenr of file extent
+	 * items.
+	 */
+	if (root->root_key.objectid == BTRFS_DATA_RELOC_TREE_OBJECTID)
+		min_alloc_size = num_bytes;
+	else
+		min_alloc_size = fs_info->sectorsize;
+
 	while (num_bytes > 0) {
 		cur_alloc_size = num_bytes;
 		ret = btrfs_reserve_extent(root, cur_alloc_size, cur_alloc_size,
-					   fs_info->sectorsize, 0, alloc_hint,
+					   min_alloc_size, 0, alloc_hint,
 					   &ins, 1, 1);
 		if (ret < 0)
 			goto out_unlock;
@@ -1361,6 +1378,8 @@ static int fallback_to_cow(struct inode *inode, struct page *locked_page,
 			   int *page_started, unsigned long *nr_written)
 {
 	const bool is_space_ino = btrfs_is_free_space_inode(BTRFS_I(inode));
+	const bool is_reloc_ino = (BTRFS_I(inode)->root->root_key.objectid ==
+				   BTRFS_DATA_RELOC_TREE_OBJECTID);
 	const u64 range_bytes = end + 1 - start;
 	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
 	u64 range_start = start;
@@ -1391,18 +1410,23 @@ static int fallback_to_cow(struct inode *inode, struct page *locked_page,
 	 *    data space info, which we incremented in the step above.
 	 *
 	 * If we need to fallback to cow and the inode corresponds to a free
-	 * space cache inode, we must also increment bytes_may_use of the data
-	 * space_info for the same reason. Space caches always get a prealloc
+	 * space cache inode or an inode of the data relocation tree, we must
+	 * also increment bytes_may_use of the data space_info for the same
+	 * reason. Space caches and relocated data extents always get a prealloc
 	 * extent for them, however scrub or balance may have set the block
-	 * group that contains that extent to RO mode.
+	 * group that contains that extent to RO mode and therefore force COW
+	 * when starting writeback.
 	 */
 	count = count_range_bits(io_tree, &range_start, end, range_bytes,
 				 EXTENT_NORESERVE, 0);
-	if (count > 0 || is_space_ino) {
-		const u64 bytes = is_space_ino ? range_bytes : count;
+	if (count > 0 || is_space_ino || is_reloc_ino) {
+		u64 bytes = count;
 		struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
 		struct btrfs_space_info *sinfo = fs_info->data_sinfo;
 
+		if (is_space_ino || is_reloc_ino)
+			bytes = range_bytes;
+
 		spin_lock(&sinfo->lock);
 		btrfs_space_info_update_bytes_may_use(fs_info, sinfo, bytes);
 		spin_unlock(&sinfo->lock);
@@ -7865,9 +7889,6 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 			dio_data.overwrite = 1;
 			inode_unlock(inode);
 			relock = true;
-		} else if (iocb->ki_flags & IOCB_NOWAIT) {
-			ret = -EAGAIN;
-			goto out;
 		}
 		ret = btrfs_delalloc_reserve_space(inode, &data_reserved,
 						   offset, count);