From: Edmund Nadolski <enadolski@suse.com>
Subject: btrfs: add missing initialization in btrfs_check_shared
References: bsc#1087185
Patch-mainline: v4.16-rc6
Git-commit: 18bf591ba9753e3e5ba91f38f756a800693408f4
This patch addresses an issue that causes fiemap to falsely
report a shared extent.
The issue occurs when 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 behavior is a regression due to the following patch:
3ec4d32 btrfs: allow backref search checks for shared extents
which was included as part of the following patch sequence:
3ec4d32 btrfs: allow backref search checks for shared extents
9dd14fd btrfs: add cond_resched() calls when resolving backrefs
0014275 btrfs: backref, add tracepoints for prelim_ref insertion and merging
6c336b2 btrfs: add a node counter to each of the rbtrees
86d5f99 btrfs: convert prelimary reference tracking to use rbtrees
f695424 btrfs: remove ref_tree implementation from backref.c
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
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.
Signed-off-by: Edmund Nadolski <enadolski@suse.com>
---
fs/btrfs/backref.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 4e89598..4a33448 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -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();
}
--
2.10.2