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 398a50f..55605c5 100644 (file)
--- 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