This is a note to let you know that I've just added the patch titled
btrfs: add missing initialization in btrfs_check_shared
to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
btrfs-add-missing-initialization-in-btrfs_check_shared.patch
and it can be found in the queue-4.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 18bf591ba9753e3e5ba91f38f756a800693408f4 Mon Sep 17 00:00:00 2001
From: Edmund Nadolski <enadolski@xxxxxxxx>
Date: Wed, 14 Mar 2018 09:03:11 -0600
Subject: btrfs: add missing initialization in btrfs_check_shared
From: Edmund Nadolski <enadolski@xxxxxxxx>
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@xxxxxxxx>
[ add text from cover letter to changelog ]
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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();
}
Patches currently in stable-queue which might be from enadolski@xxxxxxxx are
queue-4.15/btrfs-add-missing-initialization-in-btrfs_check_shared.patch