From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot0-f198.google.com (mail-ot0-f198.google.com [74.125.82.198]) by kanga.kvack.org (Postfix) with ESMTP id 580B66B0343 for ; Wed, 22 Mar 2017 08:51:56 -0400 (EDT) Received: by mail-ot0-f198.google.com with SMTP id l49so200724208otc.5 for ; Wed, 22 Mar 2017 05:51:56 -0700 (PDT) Received: from mail-ot0-x243.google.com (mail-ot0-x243.google.com. [2607:f8b0:4003:c0f::243]) by mx.google.com with ESMTPS id h65si642968oia.230.2017.03.22.05.51.55 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 22 Mar 2017 05:51:55 -0700 (PDT) Received: by mail-ot0-x243.google.com with SMTP id i50so16005029otd.0 for ; Wed, 22 Mar 2017 05:51:55 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20170322122449.54505-1-dvyukov@google.com> References: <20170322122449.54505-1-dvyukov@google.com> From: Arnd Bergmann Date: Wed, 22 Mar 2017 13:51:54 +0100 Message-ID: Subject: Re: [PATCH] x86: s/READ_ONCE_NOCHECK/READ_ONCE/ in arch_atomic_read() Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Dmitry Vyukov Cc: Andrew Morton , Andrey Ryabinin , Mark Rutland , Peter Zijlstra , Will Deacon , Linux-MM , x86@kernel.org, Linux Kernel Mailing List , kasan-dev On Wed, Mar 22, 2017 at 1:24 PM, Dmitry Vyukov 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_read(). > > Signed-off-by: Dmitry Vyukov > Reported-by: Arnd Bergmann > Reported-by: Andrey Ryabinin > Cc: Mark Rutland > Cc: Peter Zijlstra > Cc: Will Deacon > Cc: Andrey Ryabinin > Cc: Andrew Morton > 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); > } The change looks good, but the same one is needed in atomic64.h Arnd -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org