[PATCH 5/5] btrfs: split bios to the fs sector size boundary

[Christoph Hellwig <hch@lst.de>]

Btrfs like other file systems can't really deal with I/O not aligned to
it's internal block size (which strangely is called sector size in
btrfs), but the block layer split helper doesn't even know about that.

Round down the split boundary so that all I/Os are aligned.

Fixes: d5e4377d5051 ("btrfs: split zone append bios in btrfs_submit_bio")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
---
 fs/btrfs/bio.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/bio.c b/fs/btrfs/bio.c
index 0f096e226908..299b9a0ed68b 100644
--- a/fs/btrfs/bio.c
+++ b/fs/btrfs/bio.c
@@ -660,8 +660,15 @@ static u64 btrfs_append_map_length(struct btrfs_bio *bbio, u64 map_length)
 	map_length = min(map_length, bbio->fs_info->max_zone_append_size);
 	sector_offset = bio_split_rw_at(&bbio->bio, &bbio->fs_info->limits,
 					&nr_segs, map_length);
-	if (sector_offset)
-		return sector_offset << SECTOR_SHIFT;
+	if (sector_offset) {
+		/*
+		 * bio_split_rw_at could split at a size smaller than the
+		 * file system sector size and thus cause unaligned I/Os.
+		 * Fix that by always rounding down to the nearest boundary.
+		 */
+		return ALIGN_DOWN(sector_offset << SECTOR_SHIFT,
+				  bbio->fs_info->sectorsize);
+	}
 	return map_length;
 }
 
-- 
2.45.2