linux-kernel - Re: [PATCH v2] sched/numa: Fix use of spin_{un}lock

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Message-ID: <20140528065708.GK11096@twins.programming.kicks-ass.net>
Date:	Wed, 28 May 2014 08:57:08 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH v2] sched/numa: Fix use of spin_{un}lock_irq() when
 interrupts are disabled

On Tue, May 27, 2014 at 05:02:04PM -0400, Steven Rostedt wrote:
> As Peter Zijlstra told me, we have the following path:
> 
> do_exit()
>   exit_itimers()
>     itimer_delete()
>       spin_lock_irqsave(&timer->it_lock, &flags);
>       timer_delete_hook(timer);
>         kc->timer_del(timer) := posix_cpu_timer_del()
>           put_task_struct()
>             __put_task_struct()
>               task_numa_free()
>                 spin_lock(&grp->lock);
> 
> 
> Which means that task_numa_free() can be called with interrupts
> disabled, which means that we should not be using spin_lock_irq() but
> spin_lock_irqsave() instead. Otherwise we are enabling interrupts while
> holding an interrupt unsafe lock!
> 

Duh, yes. Thanks Steve!

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