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

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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: Dmitry 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Dmitry Vyukov 2018-01-29 18:26:07 +01:00 committed by Ingo Molnar
parent a35353bb9e
commit ac605bee0b
2 changed files with 25 additions and 0 deletions
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4
arch/x86/include/asm/atomic.h
View file

@ -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);
}

21
include/asm-generic/atomic-instrumented.h
View file

@ -1,3 +1,15 @@
/*
* 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)); \