On 03/21/2017 04:39 AM, Brian Foster wrote:
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.
Will do.
+ 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;
It's not an off-by-one (it's self-consistent), but your way makes more
sense, I'll fix it ;)
Thanks,
Calvin
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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