locks: add missing memory barrier in break_deleg

break_deleg is subject to the same potential race as break_lease. Add
a memory barrier to prevent it.

Signed-off-by: Jeff Layton <jlayton@primarydata.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index c3f46e499dd0..22ae79650b82 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1914,6 +1914,12 @@ static inline int break_lease(struct inode *inode, unsigned int mode)
 
 static inline int break_deleg(struct inode *inode, unsigned int mode)
 {
+        /*
+         * Since this check is lockless, we must ensure that any refcounts
+         * taken are done before checking inode->i_flock. Otherwise, we could
+         * end up racing with tasks trying to set a new lease on this file.
+         */
+        smp_mb();
         if (inode->i_flock)
                 return __break_lease(inode, mode, FL_DELEG);
         return 0;