linux-kernel - Re: mm,console: circular dependency between console

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Message-ID: <538B33D5.8070002@oracle.com>
Date:	Sun, 01 Jun 2014 10:08:21 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Jan Kara <jack@...e.cz>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: mm,console: circular dependency between console_sem and zone
 lock

On 05/12/2014 12:28 PM, Jan Kara wrote:
> On Wed 07-05-14 22:03:08, Sasha Levin wrote:
>> > Hi all,
>> > 
>> > While fuzzing with trinity inside a KVM tools guest running the latest -next
>> > kernel I've stumbled on the following spew:
>   Thanks for report. So the problem seems to be maginally valid but I'm not
> 100% sure whom to blame :). So printk() code calls up() which calls
> try_to_wake_up() under console_sem.lock spinlock. That function can take
> rq->lock which is all expected.
> 
> The next part of the chain is that during CPU initialization we call
> __sched_fork() with rq->lock which calls into hrtimer_init() which can
> allocate memory which creates a dependency rq->lock => zone.lock.rlock.
> 
> And memory management code calls printk() which zone.lock.rlock held which
> closes the loop. Now I suspect the second link in the chain can happen only
> while CPU is booting and might even happen only if some debug options are
> enabled. But I don't really know scheduler code well enough. Steven?

I've cc'ed Peter and Ingo who may be able to answer that, as it still happens
on -next.


Thanks,
Sasha
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