linux-kernel - Re: [RFC PATCH 4/4] sched: Consolidate open coded preemptible() checks

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Date:	Wed, 26 Jun 2013 15:05:11 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>, Alex Shi <alex.shi@...el.com>,
	Paul Turner <pjt@...gle.com>, Mike Galbraith <efault@....de>,
	Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [RFC PATCH 4/4] sched: Consolidate open coded preemptible()
 checks

On Thu, Jun 20, 2013 at 10:45:41PM +0200, Frederic Weisbecker wrote:
> preempt_schedule() and preempt_schedule_context() open
> code their preemptability checks.
> 
> Use the standard API instead for consolidation.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Li Zhong <zhong@...ux.vnet.ibm.com>
> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Alex Shi <alex.shi@...el.com>
> Cc: Paul Turner <pjt@...gle.com>
> Cc: Mike Galbraith <efault@....de>
> Cc: Vincent Guittot <vincent.guittot@...aro.org>
> ---
>  kernel/context_tracking.c |    3 +--
>  kernel/sched/core.c       |    4 +---
>  2 files changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
> index 6667700..08db730 100644
> --- a/kernel/context_tracking.c
> +++ b/kernel/context_tracking.c
> @@ -88,10 +88,9 @@ void user_enter(void)
>   */
>  void __sched notrace preempt_schedule_context(void)
>  {
> -	struct thread_info *ti = current_thread_info();
>  	enum ctx_state prev_ctx;
>  
> -	if (likely(ti->preempt_count || irqs_disabled()))
> +	if (likely(!preemptible()))
>  		return;
>  

#ifdef CONFIG_PREEMPT_COUNT
# define preemptible()  (preempt_count() == 0 && !irqs_disabled())
#else
# define preemptible()  0
#endif


Wouldn't that give a problem for !PREEMPT_COUNT?
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