Re: [PATCH] locking/atomics: don't alias ____ptr

From: Thomas Gleixner <tglx@linutronix.de>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Will Deacon <will.deacon@arm.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	kasan-dev <kasan-dev@googlegroups.com>,
	"x86@kernel.org" <x86@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] locking/atomics: don't alias ____ptr
Date: Wed, 28 Jun 2017 14:24:50 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.20.1706281423390.1970@nanos> (raw)
In-Reply-To: <CACT4Y+YqCP8RC9nRo5oBw2GFdFF+AVJgpcGGENR7hHL9s3GSHg@mail.gmail.com>

On Wed, 28 Jun 2017, Dmitry Vyukov wrote:
> On Wed, Jun 28, 2017 at 1:10 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> >  #define cmpxchg_local(ptr, old, new)                   \
> >  ({                                                     \
> > -       __typeof__(ptr) ____ptr = (ptr);                \
> > -       kasan_check_write(____ptr, sizeof(*____ptr));   \
> > -       arch_cmpxchg_local(____ptr, (old), (new));      \
> > +       kasan_check_write((ptr), sizeof(*(ptr)));       \
> > +       arch_cmpxchg_local((ptr), (old), (new));        \
> 
> 
> /\/\/\/\/\/\/\/\/\/\/\/\
> 
> These are macros.
> If ptr is foo(), then we will call foo() twice.

If that's true, the foo() will be evaluated a gazillion more times down the
way to the end of this macro maze.

Thanks,

	tglx