Re: console: lockup on boot

[Peter Hurley]

On 06/06/2014 03:05 PM, Sasha Levin wrote:
> 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@xxxxxxx>
> > > > AuthorDate: Thu May 22 10:43:35 2014 +1000
> > > > Commit:     Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
> > > > 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@xxxxxxx>
> > > >      Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > > >
> > > > ?
> >    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.

Sasha,

Is this bisectable? Maybe that's the best way forward here.

Regards,
Peter Hurley

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