Commit ac605bee authored by Dmitry Vyukov's avatar Dmitry Vyukov Committed by Ingo Molnar
Browse files

locking/atomic, asm-generic, x86: Add comments for atomic instrumentation 



The comments are factored out from the code changes to make them
easier to read. Add them separately to explain some non-obvious
aspects.

Signed-off-by: default avatarDmitry Vyukov <dvyukov@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: kasan-dev@googlegroups.com
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/cc595efc644bb905407012d82d3eb8bac3368e7a.1517246437.git.dvyukov@google.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent a35353bb

arch/x86/include/asm/atomic.h

+4 −0
Original line number Diff line number Diff line
@@ -24,6 +24,10 @@ 
 */

static __always_inline int arch_atomic_read(const atomic_t *v)

{

	/*

	 * Note for KASAN: we deliberately don't use READ_ONCE_NOCHECK() here,

	 * it's non-inlined function that increases binary size and stack usage.

	 */

	return READ_ONCE((v)->counter);

}

include/asm-generic/atomic-instrumented.h

+21 −0
Original line number Diff line number Diff line 
/*

 * This file provides wrappers with KASAN instrumentation for atomic operations.

 * To use this functionality an arch's atomic.h file needs to define all

 * atomic operations with arch_ prefix (e.g. arch_atomic_read()) and include

 * this file at the end. This file provides atomic_read() that forwards to

 * arch_atomic_read() for actual atomic operation.

 * Note: if an arch atomic operation is implemented by means of other atomic

 * operations (e.g. atomic_read()/atomic_cmpxchg() loop), then it needs to use

 * arch_ variants (i.e. arch_atomic_read()/arch_atomic_cmpxchg()) to avoid

 * double instrumentation.

 */



#ifndef _LINUX_ATOMIC_INSTRUMENTED_H

#define _LINUX_ATOMIC_INSTRUMENTED_H
@@ -442,6 +454,15 @@ cmpxchg64_local_size(volatile u64 *ptr, u64 old, u64 new) 
		(u64)(new)));						\

})



/*

 * Originally we had the following code here:

 *     __typeof__(p1) ____p1 = (p1);

 *     kasan_check_write(____p1, 2 * sizeof(*____p1));

 *     arch_cmpxchg_double(____p1, (p2), (o1), (o2), (n1), (n2));

 * But it leads to compilation failures (see gcc issue 72873).

 * So for now it's left non-instrumented.

 * There are few callers of cmpxchg_double(), so it's not critical.

 */

#define cmpxchg_double(p1, p2, o1, o2, n1, n2)				\

({									\

	arch_cmpxchg_double((p1), (p2), (o1), (o2), (n1), (n2));	\

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