This is a note to let you know that I've just added the patch titled
xfs: truncate pagecache before writeback in xfs_setattr_size()
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
xfs-truncate-pagecache-before-writeback-in-xfs_setattr_size.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Mon Dec 18 14:12:35 CET 2017
From: Eryu Guan <eguan@xxxxxxxxxx>
Date: Wed, 1 Nov 2017 21:43:50 -0700
Subject: xfs: truncate pagecache before writeback in xfs_setattr_size()
From: Eryu Guan <eguan@xxxxxxxxxx>
[ Upstream commit 350976ae21873b0d36584ea005076356431b8f79 ]
On truncate down, if new size is not block size aligned, we zero the
rest of block to avoid exposing stale data to user, and
iomap_truncate_page() skips zeroing if the range is already in
unwritten state or a hole. Then we writeback from on-disk i_size to
the new size if this range hasn't been written to disk yet, and
truncate page cache beyond new EOF and set in-core i_size.
The problem is that we could write data between di_size and newsize
before removing the page cache beyond newsize, as the extents may
still be in unwritten state right after a buffer write. As such, the
page of data that newsize lies in has not been zeroed by page cache
invalidation before it is written, and xfs_do_writepage() hasn't
triggered it's "zero data beyond EOF" case because we haven't
updated in-core i_size yet. Then a subsequent mmap read could see
non-zeros past EOF.
I occasionally see this in fsx runs in fstests generic/112, a
simplified fsx operation sequence is like (assuming 4k block size
xfs):
fallocate 0x0 0x1000 0x0 keep_size
write 0x0 0x1000 0x0
truncate 0x0 0x800 0x1000
punch_hole 0x0 0x800 0x800
mapread 0x0 0x800 0x800
where fallocate allocates unwritten extent but doesn't update
i_size, buffer write populates the page cache and extent is still
unwritten, truncate skips zeroing page past new EOF and writes the
page to disk, punch_hole invalidates the page cache, at last mapread
reads the block back and sees non-zero beyond EOF.
Fix it by moving truncate_setsize() to before writeback so the page
cache invalidation zeros the partial page at the new EOF. This also
triggers "zero data beyond EOF" in xfs_do_writepage() at writeback
time, because newsize has been set and page straddles the newsize.
Also fixed the wrong 'end' param of filemap_write_and_wait_range()
call while we're at it, the 'end' is inclusive and should be
'newsize - 1'.
Suggested-by: Dave Chinner <dchinner@xxxxxxxxxx>
Signed-off-by: Eryu Guan <eguan@xxxxxxxxxx>
Acked-by: Dave Chinner <dchinner@xxxxxxxxxx>
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/xfs/xfs_iops.c | 36 ++++++++++++++++++++----------------
1 file changed, 20 insertions(+), 16 deletions(-)
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -871,22 +871,6 @@ xfs_setattr_size(
return error;
/*
- * We are going to log the inode size change in this transaction so
- * any previous writes that are beyond the on disk EOF and the new
- * EOF that have not been written out need to be written here. If we
- * do not write the data out, we expose ourselves to the null files
- * problem. Note that this includes any block zeroing we did above;
- * otherwise those blocks may not be zeroed after a crash.
- */
- if (did_zeroing ||
- (newsize > ip->i_d.di_size && oldsize != ip->i_d.di_size)) {
- error = filemap_write_and_wait_range(VFS_I(ip)->i_mapping,
- ip->i_d.di_size, newsize);
- if (error)
- return error;
- }
-
- /*
* We've already locked out new page faults, so now we can safely remove
* pages from the page cache knowing they won't get refaulted until we
* drop the XFS_MMAP_EXCL lock after the extent manipulations are
@@ -902,9 +886,29 @@ xfs_setattr_size(
* user visible changes). There's not much we can do about this, except
* to hope that the caller sees ENOMEM and retries the truncate
* operation.
+ *
+ * And we update in-core i_size and truncate page cache beyond newsize
+ * before writeback the [di_size, newsize] range, so we're guaranteed
+ * not to write stale data past the new EOF on truncate down.
*/
truncate_setsize(inode, newsize);
+ /*
+ * We are going to log the inode size change in this transaction so
+ * any previous writes that are beyond the on disk EOF and the new
+ * EOF that have not been written out need to be written here. If we
+ * do not write the data out, we expose ourselves to the null files
+ * problem. Note that this includes any block zeroing we did above;
+ * otherwise those blocks may not be zeroed after a crash.
+ */
+ if (did_zeroing ||
+ (newsize > ip->i_d.di_size && oldsize != ip->i_d.di_size)) {
+ error = filemap_write_and_wait_range(VFS_I(ip)->i_mapping,
+ ip->i_d.di_size, newsize - 1);
+ if (error)
+ return error;
+ }
+
error = xfs_trans_alloc(mp, &M_RES(mp)->tr_itruncate, 0, 0, 0, &tp);
if (error)
return error;
Patches currently in stable-queue which might be from eguan@xxxxxxxxxx are
queue-4.9/ext4-fix-fdatasync-2-after-fallocate-2-operation.patch
queue-4.9/xfs-truncate-pagecache-before-writeback-in-xfs_setattr_size.patch