From 331b6d8c7afc2e5b900b9dcd850c265e1ba8d8e7 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Sun, 22 May 2016 12:48:27 +0200
Subject: [PATCH] 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>
---
include/linux/compiler.h | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 793c0829e3a390..06f27fd9d760ee 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); \
})
--
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