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[PATCH] xfs: Honor FALLOC_FL_KEEP_SIZE when punching ends of files

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  [PATCH] xfs: Honor FALLOC_FL_KEEP_SIZE when punching ends of files Calvin Owens <calvinowens@fb.com> - 2017-03-18 05:00 +0100
    [PATCH v2] xfs: Honor FALLOC_FL_KEEP_SIZE when punching ends of files Calvin Owens <calvinowens@fb.com> - 2017-03-20 06:40 +0100
      Re: [PATCH v2] xfs: Honor FALLOC_FL_KEEP_SIZE when punching ends of  files Brian Foster <bfoster@redhat.com> - 2017-03-21 12:50 +0100

#1603723 — [PATCH] xfs: Honor FALLOC_FL_KEEP_SIZE when punching ends of files

Commit 3c2bdc912a1cc050 ("xfs: kill xfs_zero_remaining_bytes") replaced
xfs_zero_remaining_bytes() with calls to iomap helpers.

Unfortunately the new iomap helpers don't enforce that [pos,count) lies
strictly on [0,i_size). This causes fallocate(mode=PUNCH_HOLE|KEEP_SIZE)
calls touching [i_size & ~PAGE_MASK, OFF_T_MAX] to round i_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

Fix this by reintroducing the checks xfs_zero_remaining_bytes() did
against i_size into xfs_zero_range().

Reported-by: Aaron Gao <gzh@fb.com>
Fixes: 3c2bdc912a1cc050 ("xfs: kill xfs_zero_remaining_bytes")
Cc: Christoph Hellwig <hch@lst.de>
Cc: <stable@vger.kernel.org> # 4.8+
Signed-off-by: Calvin Owens <calvinowens@fb.com>
---
 fs/xfs/xfs_file.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 35703a8..da7cd27 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -58,6 +58,17 @@ xfs_zero_range(
 	xfs_off_t		count,
 	bool			*did_zero)
 {
+	/*
+	 * 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.
+	 */
+	if (pos >= XFS_ISIZE(ip))
+		return 0;
+
+	if ((pos + count) >= XFS_ISIZE(ip))
+		count = XFS_ISIZE(ip) - pos - 1;
+
 	return iomap_zero_range(VFS_I(ip), pos, count, NULL, &xfs_iomap_ops);
 }
 
-- 
2.9.3

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#1604183 — [PATCH v2] xfs: Honor FALLOC_FL_KEEP_SIZE when punching ends of files

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: <stable@vger.kernel.org> # 4.8+
Signed-off-by: Calvin Owens <calvinowens@fb.com>
---
 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.
+	 */
+	if (offset >= XFS_ISIZE(ip))
+		return 0;
+
+	if ((offset + len) >= XFS_ISIZE(ip))
+		len = XFS_ISIZE(ip) - offset - 1;
+
+	/*
 	 * 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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#1605529 — Re: [PATCH v2] xfs: Honor FALLOC_FL_KEEP_SIZE when punching ends of files

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@fb.com>
> Fixes: 3c2bdc912a1cc050 ("xfs: kill xfs_zero_remaining_bytes")
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: <stable@vger.kernel.org> # 4.8+
> Signed-off-by: Calvin Owens <calvinowens@fb.com>
> ---
>  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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