Re: [PATCH 1/2] xfs: Fix missed holes in SEEK_HOLE implementation

["Darrick J. Wong" <darrick.wong@oracle.com>]

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@vger.kernel.org
> Fixes: d126d43f631f996daeee5006714fed914be32368
> Signed-off-by: Jan Kara <jack@suse.cz>

Looks ok, will test...
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--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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