Re: [PATCH] [PATCH] Gaurantee spinlocks implicit barrier for !PREEMPT_COUNT

From: Steven Rostedt <srostedt@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Vineet Gupta <Vineet.Gupta1@synopsys.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Christian Ruppert <christian.ruppert@abilis.com>,
	Pierrick Hascoet <pierrick.hascoet@abilis.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Ingo Molnar <mingo@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] [PATCH] Gaurantee spinlocks implicit barrier for !PREEMPT_COUNT
Date: Mon, 08 Apr 2013 10:59:02 -0400	[thread overview]
Message-ID: <1365433142.2733.18.camel@fedora> (raw)
In-Reply-To: <CA+55aFx88-t_pm5hbxbrrhqm3_=+JQussO=zD1kT+05UVCAFCA@mail.gmail.com>

On Mon, 2013-04-08 at 07:50 -0700, Linus Torvalds wrote:

> ---
>     diff --git a/include/linux/preempt.h b/include/linux/preempt.h
>     index 5a710b9c578e..465df1c13386 100644
>     --- a/include/linux/preempt.h
>     +++ b/include/linux/preempt.h
>     @@ -93,14 +93,17 @@ do { \
> 
>      #else /* !CONFIG_PREEMPT_COUNT */
> 
>     -#define preempt_disable() do { } while (0)
>     -#define sched_preempt_enable_no_resched() do { } while (0)
>     -#define preempt_enable_no_resched() do { } while (0)
>     -#define preempt_enable() do { } while (0)
>     -
>     -#define preempt_disable_notrace() do { } while (0)
>     -#define preempt_enable_no_resched_notrace() do { } while (0)
>     -#define preempt_enable_notrace() do { } while (0)
>     +/* This is only a barrier to other asms. Notably get_user/put_user */

Probably should add in the comment:

	" or anything else that can cause a hidden schedule. "

-- Steve

>     +#define asm_barrier() asm volatile("")
>     +
>     +#define preempt_disable() asm_barrier()
>     +#define sched_preempt_enable_no_resched() asm_barrier()
>     +#define preempt_enable_no_resched() asm_barrier()
>     +#define preempt_enable() asm_barrier()
>     +
>     +#define preempt_disable_notrace() asm_barrier()
>     +#define preempt_enable_no_resched_notrace() asm_barrier()
>     +#define preempt_enable_notrace() asm_barrier()
> 
>      #endif /* CONFIG_PREEMPT_COUNT */