linux-kernel - Re: [PATCH tip/core/rcu 13/15] rcu: Move TINY_PREEMPT_RCU away from raw_local_irq

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Message-ID: <20120831183431.GK4259@jtriplet-mobl1>
Date:	Fri, 31 Aug 2012 11:34:31 -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,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 13/15] rcu: Move TINY_PREEMPT_RCU away from
 raw_local_irq_save()

On Thu, Aug 30, 2012 at 11:56:26AM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mckenney@...aro.org>
> 
> The use of raw_local_irq_save() is unnecessary, given that local_irq_save()
> really does disable interrupts.  Also, it appears to interfere with lockdep.
> Therefore, this commit moves to local_irq_save().

It looks like the non-raw versions also include tracing, which typically
has recursive dependency problems with RCU.  Can all of these call sites
safely call into tracing without recursing back into RCU?

- Josh Triplett

> Reported-by: Fengguang Wu <fengguang.wu@...el.com>
> Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Tested-by: Fengguang Wu <fengguang.wu@...el.com>
> ---
>  kernel/rcutiny_plugin.h |   10 +++++-----
>  1 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
> index 918fd1e..3d01902 100644
> --- a/kernel/rcutiny_plugin.h
> +++ b/kernel/rcutiny_plugin.h
> @@ -278,7 +278,7 @@ static int rcu_boost(void)
>  	    rcu_preempt_ctrlblk.exp_tasks == NULL)
>  		return 0;  /* Nothing to boost. */
>  
> -	raw_local_irq_save(flags);
> +	local_irq_save(flags);
>  
>  	/*
>  	 * Recheck with irqs disabled: all tasks in need of boosting
> @@ -287,7 +287,7 @@ static int rcu_boost(void)
>  	 */
>  	if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
>  	    rcu_preempt_ctrlblk.exp_tasks == NULL) {
> -		raw_local_irq_restore(flags);
> +		local_irq_restore(flags);
>  		return 0;
>  	}
>  
> @@ -317,7 +317,7 @@ static int rcu_boost(void)
>  	t = container_of(tb, struct task_struct, rcu_node_entry);
>  	rt_mutex_init_proxy_locked(&mtx, t);
>  	t->rcu_boost_mutex = &mtx;
> -	raw_local_irq_restore(flags);
> +	local_irq_restore(flags);
>  	rt_mutex_lock(&mtx);
>  	rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */
>  
> @@ -991,9 +991,9 @@ static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
>  {
>  	unsigned long flags;
>  
> -	raw_local_irq_save(flags);
> +	local_irq_save(flags);
>  	rcp->qlen -= n;
> -	raw_local_irq_restore(flags);
> +	local_irq_restore(flags);
>  }
>  
>  /*
> -- 
> 1.7.8
> 
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