linux-kernel - Re: Linux 3.6-rc4

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Date:	Mon, 10 Sep 2012 16:36:20 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Sasha Levin <levinsasha928@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Dave Jones <davej@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Linux 3.6-rc4

On Fri, 2012-09-07 at 11:39 -0700, Linus Torvalds wrote:
> Al? Please look into this. I'm not entirely sure what's going on, but
> lockdep complains about this:
> 
>  Possible interrupt unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(&(&p->alloc_lock)->rlock);
>                                local_irq_disable();
>                                lock(&(&new_timer->it_lock)->rlock);
>                                lock(tasklist_lock);
>   <Interrupt>
>     lock(&(&new_timer->it_lock)->rlock);
> 
>  *** DEADLOCK ***
> 
> and it looks real. IOW, if I read that right, we have the task_lock ->
> it_lock dependency through exit_itimers(), and then we have the
> tasklist_lock -> task_lock dependency everywhere else. So now it_lock
> -> tasklist_lock becomes a deadlock. 

Agreed, I've got the following series from Oleg queued to solve this:

 http://marc.info/?l=linux-kernel&m=134600821828491&w=2


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