[3.13.y.z extended stable] Patch "xfs: don't zero partial page cache pages during O_DIRECT writes" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    xfs: don't zero partial page cache pages during O_DIRECT writes

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.8.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From c599619179edd9c65d62ef56eba340032db64d6a Mon Sep 17 00:00:00 2001
From: Chris Mason <clm at fb.com>
Date: Tue, 2 Sep 2014 12:12:52 +1000
Subject: xfs: don't zero partial page cache pages during O_DIRECT writes

commit 85e584da3212140ee80fd047f9058bbee0bc00d5 upstream.

xfs is using truncate_pagecache_range to invalidate the page cache
during DIO reads.  This is different from the other filesystems who
only invalidate pages during DIO writes.

truncate_pagecache_range is meant to be used when we are freeing the
underlying data structs from disk, so it will zero any partial
ranges in the page.  This means a DIO read can zero out part of the
page cache page, and it is possible the page will stay in cache.

buffered reads will find an up to date page with zeros instead of
the data actually on disk.

This patch fixes things by using invalidate_inode_pages2_range
instead.  It preserves the page cache invalidation, but won't zero
any pages.

[dchinner: catch error and warn if it fails. Comment.]

Signed-off-by: Chris Mason <clm at fb.com>
Reviewed-by: Dave Chinner <dchinner at redhat.com>
Reviewed-by: Brian Foster <bfoster at redhat.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
Signed-off-by: Dave Chinner <david at fromorbit.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/xfs/xfs_file.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 52c91e1..5825705 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -301,7 +301,16 @@ xfs_file_aio_read(
 				xfs_rw_iunlock(ip, XFS_IOLOCK_EXCL);
 				return ret;
 			}
-			truncate_pagecache_range(VFS_I(ip), pos, -1);
+
+			/*
+			 * Invalidate whole pages. This can return an error if
+			 * we fail to invalidate a page, but this should never
+			 * happen on XFS. Warn if it does fail.
+			 */
+			ret = invalidate_inode_pages2_range(VFS_I(ip)->i_mapping,
+						pos >> PAGE_CACHE_SHIFT, -1);
+			WARN_ON_ONCE(ret);
+			ret = 0;
 		}
 		xfs_rw_ilock_demote(ip, XFS_IOLOCK_EXCL);
 	}
--
1.9.1