Messages in this thread | | | Date | Mon, 27 Mar 2017 08:25:54 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH v2] x86: s/READ_ONCE_NOCHECK/READ_ONCE/ in arch_atomic[64]_read() |
| |
* Dmitry Vyukov <dvyukov@google.com> wrote:
> 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[64]_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 > Signed-off-by: Dmitry Vyukov <dvyukov@google.com> > > --- > > Changes since v1: > - also change arch_atomic64_read() > --- > arch/x86/include/asm/atomic.h | 15 ++++++--------- > arch/x86/include/asm/atomic64_64.h | 2 +- > 2 files changed, 7 insertions(+), 10 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.
s/this is deliberate choice /this is a deliberate choice
Also, the patch does not apply to the latest locking tree cleanly, due to interacting changes.
Thanks,
Ingo
| |