From 7e7fbff126d18ce2d7556f60e4b2c0b1d5d8bda3 Mon Sep 17 00:00:00 2001 From: Edmund Nadolski Date: Wed, 14 Mar 2018 09:03:11 -0600 Subject: [PATCH] btrfs: add missing initialization in btrfs_check_shared 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 [ add text from cover letter to changelog ] Signed-off-by: David Sterba Signed-off-by: Greg Kroah-Hartman --- fs/btrfs/backref.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c index b517ef1477ea..3cbca2fb1e23 100644 --- a/fs/btrfs/backref.c +++ b/fs/btrfs/backref.c @@ -1496,6 +1496,7 @@ int btrfs_check_shared(struct btrfs_root *root, u64 inum, u64 bytenr) if (!node) break; bytenr = node->val; + shared.share_count = 0; cond_resched(); } -- 2.20.1