From: Qu Wenruo wqu@suse.com
[ Upstream commit 557023ea9f06baf2659b232b08b8e8711f7001a6 ]
[BUG] When subpage compressed read write support is enabled, btrfs/038 always fails with EIO.
A simplified script can easily trigger the problem:
mkfs.btrfs -f -s 4k $dev mount $dev $mnt -o compress=lzo
xfs_io -f -c "truncate 118811" $mnt/foo xfs_io -c "pwrite -S 0x0d -b 39987 92267 39987" $mnt/foo > /dev/null
sync btrfs subvolume snapshot -r $mnt $mnt/mysnap1
xfs_io -c "pwrite -S 0x3e -b 80000 200000 80000" $mnt/foo > /dev/null sync
xfs_io -c "pwrite -S 0xdc -b 10000 250000 10000" $mnt/foo > /dev/null xfs_io -c "pwrite -S 0xff -b 10000 300000 10000" $mnt/foo > /dev/null
sync btrfs subvolume snapshot -r $mnt $mnt/mysnap2
cat $mnt/mysnap2/foo # Above cat will fail due to EIO
[CAUSE] The problem is in btrfs_submit_compressed_read().
When it tries to grab the extent map of the read range, it uses the following call:
em = lookup_extent_mapping(em_tree, page_offset(bio_first_page_all(bio)), fs_info->sectorsize);
The problem is in the page_offset(bio_first_page_all(bio)) part.
The offending inode has the following file extent layout
item 10 key (257 EXTENT_DATA 131072) itemoff 15639 itemsize 53 generation 8 type 1 (regular) extent data disk byte 13680640 nr 4096 extent data offset 0 nr 4096 ram 4096 extent compression 0 (none) item 11 key (257 EXTENT_DATA 135168) itemoff 15586 itemsize 53 generation 8 type 1 (regular) extent data disk byte 0 nr 0 item 12 key (257 EXTENT_DATA 196608) itemoff 15533 itemsize 53 generation 8 type 1 (regular) extent data disk byte 13676544 nr 4096 extent data offset 0 nr 53248 ram 86016 extent compression 2 (lzo)
And the bio passed in has the following parameters:
page_offset(bio_first_page_all(bio)) = 131072 bio_first_bvec_all(bio)->bv_offset = 65536
If we use page_offset(bio_first_page_all(bio) without adding bv_offset, we will get an extent map for file offset 131072, not 196608.
This means we read uncompressed data from disk, and later decompression will definitely fail.
[FIX] Take bv_offset into consideration when trying to grab an extent map.
And add an ASSERT() to ensure we're really getting a compressed extent.
Thankfully this won't affect anything but subpage, thus we only need to ensure this patch get merged before we enabled basic subpage support.
Reviewed-by: Anand Jain anand.jain@oracle.com Signed-off-by: Qu Wenruo wqu@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/compression.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c index f69b8d332574..f25ea4764ea1 100644 --- a/fs/btrfs/compression.c +++ b/fs/btrfs/compression.c @@ -683,6 +683,7 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio, struct page *page; struct bio *comp_bio; u64 cur_disk_byte = bio->bi_iter.bi_sector << 9; + u64 file_offset; u64 em_len; u64 em_start; struct extent_map *em; @@ -692,15 +693,17 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
em_tree = &BTRFS_I(inode)->extent_tree;
+ file_offset = bio_first_bvec_all(bio)->bv_offset + + page_offset(bio_first_page_all(bio)); + /* we need the actual starting offset of this extent in the file */ read_lock(&em_tree->lock); - em = lookup_extent_mapping(em_tree, - page_offset(bio_first_page_all(bio)), - fs_info->sectorsize); + em = lookup_extent_mapping(em_tree, file_offset, fs_info->sectorsize); read_unlock(&em_tree->lock); if (!em) return BLK_STS_IOERR;
+ ASSERT(em->compress_type != BTRFS_COMPRESS_NONE); compressed_len = em->block_len; cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS); if (!cb)