locking/barriers: Validate lockless_dereference() is used on a pointer type
authorPeter Zijlstra <peterz@infradead.org>
Sun, 22 May 2016 10:48:27 +0000 (12:48 +0200)
committerIngo Molnar <mingo@kernel.org>
Wed, 8 Jun 2016 12:22:47 +0000 (14:22 +0200)
Use the type to validate the argument @p is indeed a pointer type.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160522104827.GP3193@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
include/linux/compiler.h

index 793c0829e3a3909dd532c972e513c7b8164a16ed..06f27fd9d760eed100c0e586afdc2501b63468ab 100644 (file)
@@ -545,10 +545,14 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
  * Similar to rcu_dereference(), but for situations where the pointed-to
  * object's lifetime is managed by something other than RCU.  That
  * "something other" might be reference counting or simple immortality.
+ *
+ * The seemingly unused void * variable is to validate @p is indeed a pointer
+ * type. All pointer types silently cast to void *.
  */
 #define lockless_dereference(p) \
 ({ \
        typeof(p) _________p1 = READ_ONCE(p); \
+       __maybe_unused const void * const _________p2 = _________p1; \
        smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
        (_________p1); \
 })