From: Peter Zijlstra <peterz@infradead.org>
Date: Sun, 22 May 2016 10:48:27 +0000 (+0200)
Subject: locking/barriers: Validate lockless_dereference() is used on a pointer type
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=331b6d8c7afc2e5b900b9dcd850c265e1ba8d8e7;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git

locking/barriers: Validate lockless_dereference() is used on a pointer type

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>
---

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 793c0829e3a3..06f27fd9d760 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -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); \
 })