vfs: use lockref_get_not_zero() for optimistic lockless dget_parent()

[platform/adaptation/renesas_rcar/renesas_kernel.git] / fs / dcache.c

diff --git a/fs/dcache.c b/fs/dcache.c
index b949af8..2d24422 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -611,8 +611,23 @@ static inline void __dget(struct dentry *dentry)
 
 struct dentry *dget_parent(struct dentry *dentry)
 {
+       int gotref;
        struct dentry *ret;
 
+       /*
+        * Do optimistic parent lookup without any
+        * locking.
+        */
+       rcu_read_lock();
+       ret = ACCESS_ONCE(dentry->d_parent);
+       gotref = lockref_get_not_zero(&ret->d_lockref);
+       rcu_read_unlock();
+       if (likely(gotref)) {
+               if (likely(ret == ACCESS_ONCE(dentry->d_parent)))
+                       return ret;
+               dput(ret);
+       }
+
 repeat:
        /*
         * Don't need rcu_dereference because we re-check it was correct under