From: Miao Xie <miaox@cn.fujitsu.com>
Date: Fri, 16 Nov 2012 09:23:50 +0000 (+0800)
Subject: vfs, freeze: use ACCESS_ONCE() to guard access to ->mnt_flags
X-Git-Tag: firefly_0821_release~3680^2~1354^2~56
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=1e75529e3c6c18dc535f38454173c4f2dfa99685;p=firefly-linux-kernel-4.4.55.git

vfs, freeze: use ACCESS_ONCE() to guard access to ->mnt_flags

The compiler may optimize the while loop and make the check just be done once,
so we should use ACCESS_ONCE() to guard access to ->mnt_flags

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---

diff --git a/fs/namespace.c b/fs/namespace.c
index 398a50ff2438..55605c552787 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -313,7 +313,7 @@ int __mnt_want_write(struct vfsmount *m)
 	 * incremented count after it has set MNT_WRITE_HOLD.
 	 */
 	smp_mb();
-	while (mnt->mnt.mnt_flags & MNT_WRITE_HOLD)
+	while (ACCESS_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD)
 		cpu_relax();
 	/*
 	 * After the slowpath clears MNT_WRITE_HOLD, mnt_is_readonly will