linux-kernel - Re: [Query] Preemption (hogging) of the work handler

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Message-ID: <20160712131203.GN4695@ubuntu>
Date:	Tue, 12 Jul 2016 06:12:04 -0700
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Petr Mladek <pmladek@...e.com>, rjw@...ysocki.net
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Jan Kara <jack@...e.cz>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Tejun Heo <tj@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	vlevenetz@...sol.com, vaibhav.hiremath@...aro.org,
	alex.elder@...aro.org, johan@...nel.org, akpm@...ux-foundation.org,
	rostedt@...dmis.org, linux-pm@...r.kernel.org
Subject: Re: [Query] Preemption (hogging) of the work handler

+Rafael and linux-pm to this thread :)

On 12-07-16, 14:52, Petr Mladek wrote:
> On Tue 2016-07-12 18:38:05, Sergey Senozhatsky wrote:
> > Hello,
> > 
> > On (07/11/16 15:35), Viresh Kumar wrote:
> > [..]
> > > Sometimes, the platform doesn't come back after suspend. I have tried
> > > enabling no-console-suspend and the last line it prints is:
> > > 
> > >         Disabling non-boot CPUs
> 
> I guess that the printk() kthread is not longer scheduled when there
> is only one CPU left.

Yeah, so I tried debugging this more and I am able to get printing
done to just before arch_suspend_disable_irqs() in suspend.c and then
it stops because of the async nature.

I get to this point for both successful suspend/resume (where system
resumes back successfully) and in the bad case (where the system just
hangs/crashes).

FWIW, I also tried commenting out following in suspend_enter():

        error = suspend_ops->enter(state);

so that the system doesn't go into suspend at all, and just resume
back immediately (similar to TEST_CORE) and I saw the hang/crash then
as well one of the times.

> We might try to explicitly flush the consoles in suspend_console().

That wouldn't happen as I have disabled console-suspend.

> But I am not sure if we always want to do so because it might take
> a while. Also it need not help if someone already owns the
> console_sem. Note the console_unlock() calls the cond_resched()
> when in safe context.
> 
> Well, we might do the best effort when no_console_suspend is enabled.

Hmm.. I have no reasoning yet on why the system comes to a complete
stop and a forceful reboot only makes it work :(

-- 
viresh