Messages in this thread Patch in this message | | | From | Dmitry Vyukov <> | Subject | [PATCH] x86: s/READ_ONCE_NOCHECK/READ_ONCE/ in arch_atomic_read() | Date | Wed, 22 Mar 2017 13:24:49 +0100 |
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Two problems was reported with READ_ONCE_NOCHECK in arch_atomic_read: 1. Andrey Ryabinin reported significant binary size increase (+400K of text). READ_ONCE_NOCHECK is intentionally compiled to non-inlined function call, and I counted 640 copies of it in my vmlinux. 2. Arnd Bergmann reported a new splat of too large frame sizes.
A single inlined KASAN check is very cheap, a non-inlined function call with KASAN/KCOV instrumentation can easily be more expensive.
Switch to READ_ONCE() in arch_atomic_read().
Signed-off-by: Dmitry Vyukov <dvyukov@google.com> Reported-by: Arnd Bergmann <arnd@arndb.de> Reported-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will.deacon@arm.com> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: linux-mm@kvack.org Cc: x86@kernel.org Cc: linux-kernel@vger.kernel.org Cc: kasan-dev@googlegroups.com --- arch/x86/include/asm/atomic.h | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-)
diff --git a/arch/x86/include/asm/atomic.h b/arch/x86/include/asm/atomic.h index 0cde164f058a..46e53bbf7ce3 100644 --- a/arch/x86/include/asm/atomic.h +++ b/arch/x86/include/asm/atomic.h @@ -24,10 +24,13 @@ static __always_inline int arch_atomic_read(const atomic_t *v) { /* - * We use READ_ONCE_NOCHECK() because atomic_read() contains KASAN - * instrumentation. Double instrumentation is unnecessary. + * Note: READ_ONCE() here leads to double instrumentation as + * both READ_ONCE() and atomic_read() contain instrumentation. + * This is deliberate choice. READ_ONCE_NOCHECK() is compiled to a + * non-inlined function call that considerably increases binary size + * and stack usage under KASAN. */ - return READ_ONCE_NOCHECK((v)->counter); + return READ_ONCE((v)->counter); } /** @@ -39,12 +42,6 @@ static __always_inline int arch_atomic_read(const atomic_t *v) */ static __always_inline void arch_atomic_set(atomic_t *v, int i) { - /* - * We could use WRITE_ONCE_NOCHECK() if it exists, similar to - * READ_ONCE_NOCHECK() in arch_atomic_read(). But there is no such - * thing at the moment, and introducing it for this case does not - * worth it. - */ WRITE_ONCE(v->counter, i); } -- 2.12.1.500.gab5fba24ee-goog
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