linux-kernel - Re: Linux 3.6-rc4

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Message-ID: <CA+1xoqcY5=Ru-pgSGux0rGEp8d2nOWFpqk3EW9j=Qt2N6=XECw@mail.gmail.com>
Date:	Sat, 15 Sep 2012 14:25:51 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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 Mon, Sep 10, 2012 at 4:36 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> 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

I'm still seeing lockdep warnings even with the code above applied.
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