提交 18bf591b 编写于 作者: E Edmund Nadolski 提交者: David Sterba

btrfs: add missing initialization in btrfs_check_shared

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: 3ec4d323 ("btrfs: allow backref search checks for shared extents")
Signed-off-by: NEdmund Nadolski <enadolski@suse.com>
[ add text from cover letter to changelog ]
Signed-off-by: NDavid Sterba <dsterba@suse.com>
上级 047fdea6
......@@ -1519,6 +1519,7 @@ int btrfs_check_shared(struct btrfs_root *root, u64 inum, u64 bytenr)
if (!node)
break;
bytenr = node->val;
shared.share_count = 0;
cond_resched();
}
......
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