linux-kernel - Re: [PATCH tip/core/rcu 15/26] alpha: Fix preemption handling in idle loop

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Date:	Fri, 31 Aug 2012 16:55:46 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, sbw@....edu, patches@...aro.org,
	Richard Henderson <rth@...ddle.net>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Matt Turner <mattst88@...il.com>,
	alpha <linux-alpha@...r.kernel.org>,
	Michael Cree <mcree@...on.net.nz>
Subject: Re: [PATCH tip/core/rcu 15/26] alpha: Fix preemption handling in
 idle loop

On Thu, Aug 30, 2012 at 02:05:32PM -0700, Paul E. McKenney wrote:
> From: Frederic Weisbecker <fweisbec@...il.com>
> 
> cpu_idle() is called on the boot CPU by the init code with
> preemption disabled. But the cpu_idle() function in alpha
> doesn't handle this when it calls schedule() directly.
> 
> Fix it by converting it into schedule_preempt_disabled().
> 
> Also disable preemption before calling cpu_idle() from
> secondary CPU entry code to stay consistent with this
> state.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Richard Henderson <rth@...ddle.net>
> Cc: Ivan Kokshaysky <ink@...assic.park.msu.ru>
> Cc: Matt Turner <mattst88@...il.com>
> Cc: alpha <linux-alpha@...r.kernel.org>
> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Michael Cree <mcree@...on.net.nz>

Reviewed-by: Josh Triplett <josh@...htriplett.org>

>  arch/alpha/kernel/process.c |    3 ++-
>  arch/alpha/kernel/smp.c     |    1 +
>  2 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
> index 153d3fc..eac5e01 100644
> --- a/arch/alpha/kernel/process.c
> +++ b/arch/alpha/kernel/process.c
> @@ -56,7 +56,8 @@ cpu_idle(void)
>  
>  		while (!need_resched())
>  			cpu_relax();
> -		schedule();
> +
> +		schedule_preempt_disabled();
>  	}
>  }
>  
> diff --git a/arch/alpha/kernel/smp.c b/arch/alpha/kernel/smp.c
> index 35ddc02..a41ad90 100644
> --- a/arch/alpha/kernel/smp.c
> +++ b/arch/alpha/kernel/smp.c
> @@ -166,6 +166,7 @@ smp_callin(void)
>  	DBGS(("smp_callin: commencing CPU %d current %p active_mm %p\n",
>  	      cpuid, current, current->active_mm));
>  
> +	preempt_disable();
>  	/* Do nothing.  */
>  	cpu_idle();
>  }
> -- 
> 1.7.8
> 
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