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From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>,
	mingo@kernel.org, torvalds@linux-foundation.org,
	tglx@linutronix.de, ilya.dryomov@inktank.com,
	linux-kernel@vger.kernel.org, Eric Paris <eparis@redhat.com>,
	rafael.j.wysocki@intel.com
Subject: Re: [PATCH 00/11] nested sleeps, fixes and debug infrastructure
Date: Tue, 28 Oct 2014 09:23:35 +0100	[thread overview]
Message-ID: <20141028082335.GM3337@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20141028000703.GA22964@redhat.com>

On Tue, Oct 28, 2014 at 01:07:03AM +0100, Oleg Nesterov wrote:
> 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.

> 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().

I'm not sure those two would interact, yes, both would first set either
the freezable or stop bit and then wake. If both were to race, all we
need to ensure is to check both before calling schedule again.

A loop like:

	while (!kthread_should_stop()) {
		wait_event_freezable(wq, cond);
	}

Would satisfy that, because even if kthread_should_stop() gets set first
and then freezing happens and we get into try_to_freeze() first, we'd
still to the kthread_should_stop() check right after we thaw.

So I don't se a reason to collect both stop and freeze into a single
thing.

> 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.

Right.

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

So I talked to Rafael yesterday and I'm going to replace all the
wait_event*() stuff, and I suppose also freezable_schedule() because
they're racy.

The moment we call freezer_do_not_count() the freezer will ignore us,
this means the thread could still be running (albeit not for long) when
the freezer reports success.

Ideally I'll be able to kill the entire freezer_do_not_count() stuff.

  reply	other threads:[~2014-10-28  8:23 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-24  8:18 [PATCH 00/11] nested sleeps, fixes and debug infrastructure Peter Zijlstra
2014-09-24  8:18 ` [PATCH 01/11] locking/mutex: Dont assume TASK_RUNNING Peter Zijlstra
2014-10-28 11:09   ` [tip:sched/core] locking/mutex: Don't " tip-bot for Peter Zijlstra
2014-09-24  8:18 ` [PATCH 02/11] wait: Provide infrastructure to deal with nested blocking Peter Zijlstra
2014-09-29 21:02   ` Oleg Nesterov
2014-10-02  7:37     ` Peter Zijlstra
2014-10-02 21:21       ` Oleg Nesterov
2014-10-28 11:09   ` [tip:sched/core] sched/wait: " tip-bot for Peter Zijlstra
2014-09-24  8:18 ` [PATCH 03/11] wait: Add might_sleep() Peter Zijlstra
2014-10-28 11:09   ` [tip:sched/core] sched/wait: Add might_sleep() checks tip-bot for Peter Zijlstra
2014-09-24  8:18 ` [PATCH 04/11] exit: Deal with nested sleeps Peter Zijlstra
2014-10-28 11:10   ` [tip:sched/core] sched, " tip-bot for Peter Zijlstra
2014-09-24  8:18 ` [PATCH 05/11] inotify: " Peter Zijlstra
2014-10-28 11:10   ` [tip:sched/core] sched, " tip-bot for Peter Zijlstra
2014-09-24  8:18 ` [PATCH 06/11] tty: " Peter Zijlstra
2014-10-28 11:10   ` [tip:sched/core] sched, " tip-bot for Peter Zijlstra
2014-09-24  8:18 ` [PATCH 07/11] smp: Correctly deal " Peter Zijlstra
2014-10-28 11:11   ` [tip:sched/core] sched, " tip-bot for Peter Zijlstra
2014-09-24  8:18 ` [PATCH 08/11] module: Fix nested sleep Peter Zijlstra
2014-09-29 22:18   ` Oleg Nesterov
2014-09-30 13:43     ` Peter Zijlstra
2014-10-28 11:11   ` [tip:sched/core] sched, modules: Fix nested sleep in add_unformed_module() tip-bot for Peter Zijlstra
2014-09-24  8:18 ` [PATCH 09/11] net: Clean up sk_wait_event() vs might_sleep() Peter Zijlstra
2014-09-24  8:36   ` Peter Zijlstra
2014-10-28 11:11   ` [tip:sched/core] sched, net: Clean up sk_wait_event() vs. might_sleep() tip-bot for Peter Zijlstra
2014-09-24  8:18 ` [PATCH 10/11] sched: Debug nested sleeps Peter Zijlstra
2014-09-29 22:13   ` Oleg Nesterov
2014-09-30 13:49     ` Peter Zijlstra
2014-09-30 21:47       ` Oleg Nesterov
2014-10-01 16:10         ` Peter Zijlstra
2014-10-01 18:35           ` Oleg Nesterov
2014-10-02  9:07             ` Peter Zijlstra
2014-10-02 21:34               ` Oleg Nesterov
2014-10-28 11:11   ` [tip:sched/core] " tip-bot for Peter Zijlstra
2014-09-24  8:18 ` [PATCH 11/11] sched: Exclude cond_resched() from nested sleep test Peter Zijlstra
2014-10-28 11:12   ` [tip:sched/core] " tip-bot for Peter Zijlstra
2014-09-25  8:30 ` [PATCH 00/11] nested sleeps, fixes and debug infrastructure Mike Galbraith
2014-09-25  9:06   ` Peter Zijlstra
2014-09-25  9:10     ` Mike Galbraith
2014-09-25  9:15     ` Peter Zijlstra
2014-09-25  9:56       ` Mike Galbraith
2014-09-25 13:59         ` BUG: sleeping function called from invalid context at drivers/cpufreq/cpufreq.c:370 Mike Galbraith
2014-09-26  6:24           ` Mike Galbraith
2014-09-26  7:54             ` Mike Galbraith
2014-09-26 14:10               ` Rafael J. Wysocki
2014-09-26 22:44               ` Rafael J. Wysocki
2014-09-27  6:14                 ` Mike Galbraith
2014-09-27 19:57                   ` Rafael J. Wysocki
2014-10-02 10:22       ` [PATCH 00/11] nested sleeps, fixes and debug infrastructure Peter Zijlstra
2014-10-02 12:15         ` Peter Zijlstra
2014-10-27 13:41           ` Peter Zijlstra
2014-10-28  0:07             ` Oleg Nesterov
2014-10-28  8:23               ` Peter Zijlstra [this message]
2014-10-29  0:00                 ` Oleg Nesterov
2014-10-29  9:35                   ` Peter Zijlstra
2014-10-29 11:31                     ` Peter Zijlstra
2014-10-29 11:36                       ` Peter Zijlstra
2014-10-29 14:26                   ` Peter Zijlstra
2014-11-04 16:08         ` [tip:sched/core] audit, sched/wait: Fixup kauditd_thread() wait loop tip-bot for Peter Zijlstra

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