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: Wed, 29 Oct 2014 15:26:54 +0100 [thread overview]
Message-ID: <20141029142654.GD3337@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20141029000055.GA12107@redhat.com>
On Wed, Oct 29, 2014 at 01:00:56AM +0100, Oleg Nesterov wrote:
> On 10/28, Peter Zijlstra wrote:
> > 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.
>
> Yes, sure. IIRC the theory was that a PF_FREEZER_SKIP will do nothing
> "wrong" wrt freezing/suspend before it actually sleeps, but I guess
> today we can't assume this.
Esp. the wait_event_freezable*() family seems suspicious in that the
cond stmt can actually result in quite a lot of code.
But see below, I don't think we have a guarantee it will _ever_ sleep.
Also, this calls schedule(); try_to_freeze() in a suitable loop that's
safe against spurious wakeups, OTOH..
> > Ideally I'll be able to kill the entire freezer_do_not_count() stuff.
>
> Agreed... but it is not clear to me what exactly we can/should do.
.. I looked at freezable_schedule() and I'm not sure how to 'fix' that.
The problem being things like signal.c:ptrace_stop() that will actually
misbehave in the face of spurious wakeups as allowed by try_to_freeze().
Then again, freezable_schedule() isn't nearly as bad as the
wait_event_freezable() stuff because it does indeed guarantee the task
only calls schedule().
Then again, it is possible to miss these tasks and report freeze success
with a running task all the same, suppose its already woken but
preempted before freezer_count(). The for_each_process_thread() loop in
try_to_freeze_tasks() will skip over it.
And all I can come up with is horrible.. maybe for another day.
next prev parent reply other threads:[~2014-10-29 14:27 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
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 [this message]
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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