On Sun, Mar 19, 2017 at 09:54:51PM -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@xxxxxx>
> Fixes: 3c2bdc912a1cc050 ("xfs: kill xfs_zero_remaining_bytes")
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.8+
> Signed-off-by: Calvin Owens <calvinowens@xxxxxx>
> ---
> fs/xfs/xfs_bmap_util.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index 8b75dce..0796ebc 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -1309,6 +1309,17 @@ xfs_free_file_space(
> }
>
> /*
> + * Avoid doing I/O beyond eof - it's not necessary
> + * since nothing can read beyond eof. The space will
> + * be zeroed when the file is extended anyway.
> + */
I'd suggest to update the comment below with this information and move
the following bits down below it as well.
> + if (offset >= XFS_ISIZE(ip))
> + return 0;
> +
> + if ((offset + len) >= XFS_ISIZE(ip))
> + len = XFS_ISIZE(ip) - offset - 1;
> +
This looks like an off-by-one. Do you mean the following?
if (offset + len > XFS_ISIZE(ip))
len = XFS_ISIZE(ip) - offset;
Brian
> + /*
> * 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.
> --
> 2.9.3
>
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