On Thu, May 11, 2017 at 06:50:22PM +0200, Jan Kara wrote:
> XFS SEEK_HOLE implementation could miss a hole in an unwritten extent as
> can be seen by the following command:
>
> xfs_io -c "falloc 0 256k" -c "pwrite 0 56k" -c "pwrite 128k 8k"
> -c "seek -h 0" file
> wrote 57344/57344 bytes at offset 0
> 56 KiB, 14 ops; 0.0000 sec (49.312 MiB/sec and 12623.9856 ops/sec)
> wrote 8192/8192 bytes at offset 131072
> 8 KiB, 2 ops; 0.0000 sec (70.383 MiB/sec and 18018.0180 ops/sec)
> Whence Result
> HOLE 139264
>
> Where we can see that hole at offset 56k was just ignored by SEEK_HOLE
> implementation. The bug is in xfs_find_get_desired_pgoff() which does
> not properly detect the case when a first page in the pagevec has larger
> index than expected (and even if the condition was right, we would fail
> to update the returned offset).
>
> Fix the problem by properly detecting when found page has larger offset
> than expected.
>
> CC: stable@xxxxxxxxxxxxxxx
> Fixes: d126d43f631f996daeee5006714fed914be32368
> Signed-off-by: Jan Kara <jack@xxxxxxx>
Looks ok, will test...
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--D
> ---
> fs/xfs/xfs_file.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 35703a801372..df51c025adfe 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -1077,13 +1077,12 @@ xfs_find_get_desired_pgoff(
> }
>
> /*
> - * At lease we found one page. If this is the first time we
> - * step into the loop, and if the first page index offset is
> - * greater than the given search offset, a hole was found.
> + * At least we found one page. If the current offset is smaller
> + * than the first page offset, a hole was found.
> */
> - if (type == HOLE_OFF && lastoff == startoff &&
> - lastoff < page_offset(pvec.pages[0])) {
> + if (type == HOLE_OFF && lastoff < page_offset(pvec.pages[0])) {
> found = true;
> + *offset = lastoff;
> break;
> }
>
> --
> 2.12.0
>
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