linux-kernel - Re: [PATCH 00/11] nested sleeps, fixes and debug infrastructure

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Date:	Tue, 28 Oct 2014 01:07:03 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mike Galbraith <umgwanakikbuti@...il.com>, mingo@...nel.org,
	torvalds@...ux-foundation.org, tglx@...utronix.de,
	ilya.dryomov@...tank.com, linux-kernel@...r.kernel.org,
	Eric Paris <eparis@...hat.com>, rafael.j.wysocki@...el.com
Subject: Re: [PATCH 00/11] nested sleeps, fixes and debug infrastructure

On 10/27, Peter Zijlstra wrote:
>
> On Thu, Oct 02, 2014 at 02:15:53PM +0200, Peter Zijlstra wrote:
> > On Thu, Oct 02, 2014 at 12:22:51PM +0200, Peter Zijlstra wrote:
>
> > > +#define __wait_event_freezable(wq, condition)				\
> > > +	(void)___wait_event(wq, condition, TASK_INTERRUPTIBLE, 0, 0,	\
> > > +			    schedule(); try_to_freeze())
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

see below.

> > > +
> > > +/**
> > > + * wait_event - sleep until a condition gets true or freeze (for kthreads)
> > > + * @wq: the waitqueue to wait on
> > > + * @condition: a C expression for the event to wait for
> > > + *
> > > + * The process is put to sleep (TASK_INTERRUPTIBLE -- so as not to contribute
> > > + * to system load) until the @condition evaluates to true. The
> > > + * @condition is checked each time the waitqueue @wq is woken up.
> > > + *
> > > + * wake_up() has to be called after changing any variable that could
> > > + * change the result of the wait condition.
> > > + */
> > > +#define wait_event_freezable(wq, condition)				\
> > > +do {									\
> > > +	WARN_ON_ONCE(!(current->flags & PF_KTHREAD));			\
> > > +	might_sleep();							\
> > > +	if (condition)							\
> > > +		break;							\
> > > +	__wait_event_freezable(wq, condition);				\
> > > +} while (0)
> > > +
> > >  #define __wait_event_timeout(wq, condition, timeout)			\
> > >  	___wait_event(wq, ___wait_cond_timeout(condition),		\
> > >  		      TASK_UNINTERRUPTIBLE, 0, timeout,			\
> >
> > Bah, that doesn't compile, because there already appears to be one,
> > hidden in freezer.h. Now I can't actually tell if it does the same thing
> > or not.
> >
> > Rafael?
>
> Ping?

I was going to say that wait_event_freezable() in kauditd_thread()
is not friendly wrt kthread_should_stop() and thus we we need
kthread_freezable_should_stop().

But in fact we never stop this kauditd_task, so I think we should
turn the main loop into "for (;;)" and change this code to use
wait_event_freezable() like your patch does.

Perhaps it also makes sense to redefine wait_event_freezable.*()
via ___wait_event(cmd => freezable_schedule), but I think this needs
another patch.

Oleg.

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