linux-kernel - Re: [BUG] circular lock dependency in tip

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Date:	Wed, 18 Mar 2009 17:51:11 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [BUG] circular lock dependency in tip

On Wed, 18 Mar 2009, Steven Rostedt wrote:
> 
> 
> Seems that the issue is that we have:
> 
> static void idle_balance(int this_cpu, struct rq *this_rq)
> {
>         struct sched_domain *sd;
>         int pulled_task = 0;
>         unsigned long next_balance = jiffies + HZ;
>         cpumask_var_t tmpmask;
> 
>         if (!alloc_cpumask_var(&tmpmask, GFP_ATOMIC))
>                 return;

Is this really a good idea? I mean, if the system is very active, it can 
easily fail to acquire memory, you just need to have cache filled. 
Remember, this is GFP_ATOMIC, if the memory is not available, then we do 
not try to reclaim. With the system busy, this may be exactly the time we 
need to do the idle_balance.

I'm thinking a blind conversion of cpumask_var_t is not the best way to 
handle changes. This is as bad as fixing compiler warnings without looking 
into the real cause.

-- Steve

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