linux-kernel - Re: console: lockup on boot

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Date:	Fri, 06 Jun 2014 15:05:58 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Jan Kara <jack@...e.cz>, Peter Hurley <peter@...leysoftware.com>
CC:	pmladek@...e.cz, Andrew Morton <akpm@...ux-foundation.org>,
	Jet Chen <jet.chen@...el.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: console: lockup on boot

On 05/30/2014 10:07 AM, Jan Kara wrote:
> On Fri 30-05-14 09:58:14, Peter Hurley wrote:
>> > On 05/30/2014 09:11 AM, Sasha Levin wrote:
>>> > >Hi all,
>>> > >
>>> > >I sometime see lockups when booting my KVM guest with the latest -next kernel,
>>> > >it basically hangs right when it should start 'init', and after a while I get
>>> > >the following spew:
>>> > >
>>> > >[   30.790833] BUG: spinlock lockup suspected on CPU#1, swapper/1/0
>> > 
>> > Maybe related to this report: https://lkml.org/lkml/2014/5/30/26
>> > from Jet Chen which was bisected to
>> > 
>> > commit bafe980f5afc7ccc693fd8c81c8aa5a02fbb5ae0
>> > Author:     Jan Kara <jack@...e.cz>
>> > AuthorDate: Thu May 22 10:43:35 2014 +1000
>> > Commit:     Stephen Rothwell <sfr@...b.auug.org.au>
>> > CommitDate: Thu May 22 10:43:35 2014 +1000
>> > 
>> >     printk: enable interrupts before calling console_trylock_for_printk()
>> >         We need interrupts disabled when calling console_trylock_for_printk() only
>> >     so that cpu id we pass to can_use_console() remains valid (for other
>> >     things console_sem provides all the exclusion we need and deadlocks on
>> >     console_sem due to interrupts are impossible because we use
>> >     down_trylock()).  However if we are rescheduled, we are guaranteed to run
>> >     on an online cpu so we can easily just get the cpu id in
>> >     can_use_console().
>> >         We can lose a bit of performance when we enable interrupts in
>> >     vprintk_emit() and then disable them again in console_unlock() but OTOH it
>> >     can somewhat reduce interrupt latency caused by console_unlock()
>> >     especially since later in the patch series we will want to spin on
>> >     console_sem in console_trylock_for_printk().
>> >         Signed-off-by: Jan Kara <jack@...e.cz>
>> >     Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
>> > 
>> > ?
>   Yeah, very likely. I think I see the problem, I'll send the fix shortly.

Hi Jan,

It seems that the issue I'm seeing is different from the "[prink]  BUG: spinlock
lockup suspected on CPU#0, swapper/1".

Is there anything else I could try here? The issue is very common during testing.


Thanks,
Sasha
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