4.15-stable review patch. If anyone has any objections, please let me know.
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From: Edmund Nadolski enadolski@suse.com
commit 18bf591ba9753e3e5ba91f38f756a800693408f4 upstream.
This patch addresses an issue that causes fiemap to falsely report a shared extent. The test case is as follows:
xfs_io -f -d -c "pwrite -b 16k 0 64k" -c "fiemap -v" /media/scratch/file5 sync xfs_io -c "fiemap -v" /media/scratch/file5
which gives the resulting output:
wrote 65536/65536 bytes at offset 0 64 KiB, 4 ops; 0.0000 sec (121.359 MiB/sec and 7766.9903 ops/sec) /media/scratch/file5: EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS 0: [0..127]: 24576..24703 128 0x2001 /media/scratch/file5: EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS 0: [0..127]: 24576..24703 128 0x1
This is because btrfs_check_shared calls find_parent_nodes repeatedly in a loop, passing a share_check struct to report the count of shared extent. But btrfs_check_shared does not re-initialize the count value to zero for subsequent calls from the loop, resulting in a false share count value. This is a regressive behavior from 4.13.
With proper re-initialization the test result is as follows:
wrote 65536/65536 bytes at offset 0 64 KiB, 4 ops; 0.0000 sec (110.035 MiB/sec and 7042.2535 ops/sec) /media/scratch/file5: EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS 0: [0..127]: 24576..24703 128 0x1 /media/scratch/file5: EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS 0: [0..127]: 24576..24703 128 0x1
which corrects the regression.
Fixes: 3ec4d3238ab ("btrfs: allow backref search checks for shared extents") Signed-off-by: Edmund Nadolski enadolski@suse.com [ add text from cover letter to changelog ] Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/btrfs/backref.c | 1 + 1 file changed, 1 insertion(+)
--- a/fs/btrfs/backref.c +++ b/fs/btrfs/backref.c @@ -1509,6 +1509,7 @@ int btrfs_check_shared(struct btrfs_root if (!node) break; bytenr = node->val; + shared.share_count = 0; cond_resched(); }