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SubjectRe: [PATCH v3] xfs: Honor FALLOC_FL_KEEP_SIZE when punching ends of files
On Thu, Mar 30, 2017 at 09:18:00PM -0700, Calvin Owens wrote:
> When punching past EOF on XFS, fallocate(mode=PUNCH_HOLE|KEEP_SIZE) will
> round the file size up to the nearest multiple of PAGE_SIZE:
>
> calvinow@vm-disks/generic-xfs-1 ~$ dd if=/dev/urandom of=test bs=2048 count=1
> calvinow@vm-disks/generic-xfs-1 ~$ stat test
> Size: 2048 Blocks: 8 IO Block: 4096 regular file
> calvinow@vm-disks/generic-xfs-1 ~$ fallocate -n -l 2048 -o 2048 -p test
> calvinow@vm-disks/generic-xfs-1 ~$ stat test
> Size: 4096 Blocks: 8 IO Block: 4096 regular file
>
> Commit 3c2bdc912a1cc050 ("xfs: kill xfs_zero_remaining_bytes") replaced
> xfs_zero_remaining_bytes() with calls to iomap helpers. The new helpers
> don't enforce that [pos,offset) lies strictly on [0,i_size) when being
> called from xfs_free_file_space(), so by "leaking" these ranges into
> xfs_zero_range() we get this buggy behavior.
>
> Fix this by reintroducing the checks xfs_zero_remaining_bytes() did
> against i_size at the bottom of xfs_free_file_space().
>
> Reported-by: Aaron Gao <gzh@fb.com>
> Fixes: 3c2bdc912a1cc050 ("xfs: kill xfs_zero_remaining_bytes")
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Brian Foster <bfoster@redhat.com>
> Cc: <stable@vger.kernel.org> # 4.8+
> Signed-off-by: Calvin Owens <calvinowens@fb.com>
> ---
> fs/xfs/xfs_bmap_util.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index 8b75dce..828532c 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -1311,8 +1311,16 @@ xfs_free_file_space(
> /*
> * Now that we've unmap all full blocks we'll have to zero out any
> * partial block at the beginning and/or end. xfs_zero_range is
> - * smart enough to skip any holes, including those we just created.
> + * smart enough to skip any holes, including those we just created,
> + * but we must take care not to zero beyond EOF and enlarge i_size.
> */
> +
> + if (offset >= XFS_ISIZE(ip))
> + return 0;
> +
> + if (offset + len > XFS_ISIZE(ip))
> + len = XFS_ISIZE(ip) - offset;
> +

I'll pick this up for 4.12.
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> return xfs_zero_range(ip, offset, len, NULL);
> }
>
> --
> 2.9.3
>
> --
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