rcu: Make kfree_rcu() ignore NULL pointers

This commit makes the kfree_rcu() macro's semantics be consistent
with the likes of kfree() by adding a check for NULL pointers, so
that kfree_rcu(NULL, ...) is a no-op.

Reported-by: Andriy Shevchenko <andriy.shevchenko@linux.intel.com>
Reported-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Reviewed-by: Andriy Shevchenko <andriy.shevchenko@linux.intel.com>

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 922bb6848813301c29211f0aca1dbfe79de02f4c..915460ec08722c3aa5434eb0814e33793d5a2103 100644 (file)
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -805,7 +805,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
 /**
  * kfree_rcu() - kfree an object after a grace period.
  * @ptr:       pointer to kfree
- * @rcu_head:  the name of the struct rcu_head within the type of @ptr.
+ * @rhf:       the name of the struct rcu_head within the type of @ptr.
  *
  * Many rcu callbacks functions just call kfree() on the base structure.
  * These functions are trivial, but their size adds up, and furthermore
@@ -828,9 +828,13 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  * The BUILD_BUG_ON check must not involve any function calls, hence the
  * checks are done in macros here.
  */
-#define kfree_rcu(ptr, rcu_head)                                       \
-       __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
-
+#define kfree_rcu(ptr, rhf)                                            \
+do {                                                                   \
+       typeof (ptr) ___p = (ptr);                                      \
+                                                                       \
+       if (___p)                                                       \
+               __kfree_rcu(&((___p)->rhf), offsetof(typeof(*(ptr)), rhf)); \
+} while (0)
 
 /*
  * Place this after a lock-acquisition primitive to guarantee that