From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: umgwanakikbuti@gmail.com, mingo@elte.hu, ktkhai@parallels.com,
rostedt@goodmis.org, tglx@linutronix.de, juri.lelli@gmail.com,
pang.xunlei@linaro.org, wanpeng.li@linux.intel.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 08/14] hrtimer: Allow hrtimer::function() to free the timer
Date: Mon, 8 Jun 2015 12:55:14 +0200 [thread overview]
Message-ID: <20150608105514.GV18673@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20150608091417.GM19282@twins.programming.kicks-ass.net>
On Mon, Jun 08, 2015 at 11:14:17AM +0200, Peter Zijlstra wrote:
> On Mon, Jun 08, 2015 at 12:33:17AM +0200, Oleg Nesterov wrote:
> > Not sure I read this patch correctly, it doesn't apply to Linus's tree.
>
> I was working on tip/master, there's a number of timer patches in there.
>
> > And I simply can not understand the complication in hrtimer_active(),
> > please help!
> >
> > On 06/05, Peter Zijlstra wrote:
> > >
> > > +bool hrtimer_active(const struct hrtimer *timer)
> > > +{
> > > + struct hrtimer_cpu_base *cpu_base;
> > > + unsigned int seq;
> > > + bool active;
> > > +
> > > + do {
> > > + active = false;
> > > + cpu_base = READ_ONCE(timer->base->cpu_base);
> > > + seq = raw_read_seqcount(&cpu_base->seq);
> > > +
> > > + if (timer->state != HRTIMER_STATE_INACTIVE ||
> > > + cpu_base->running == timer)
> > > + active = true;
> >
> > Why we can't simply return true in this case?
> >
> > Unless you lock this timer, hrtimer_active() is inherently racy anyway.
> > Granted, it must not wrongly return False if the timer is pending or
> > running.
> >
> > But "false positive" does not differ from the case when (say) the
> > running timer->function() finishes right after hrtimer_active() returns
> > True.
OK I can't read; you asked why delay the return true inside that loop.
Yes we can as per your argument. I think I ended up being too paranoid
or something.
next prev parent reply other threads:[~2015-06-08 10:55 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-05 8:48 [PATCH 00/14] sched: balance callbacks Peter Zijlstra
2015-06-05 8:48 ` [PATCH 01/14] sched: Replace post_schedule with a balance callback list Peter Zijlstra
2015-06-05 8:48 ` [PATCH 02/14] sched: Use replace normalize_task() with __sched_setscheduler() Peter Zijlstra
2015-06-05 8:48 ` [PATCH 03/14] sched: Allow balance callbacks for check_class_changed() Peter Zijlstra
2015-06-05 8:48 ` [PATCH 04/14] sched,rt: Remove return value from pull_rt_task() Peter Zijlstra
2015-06-05 8:48 ` [PATCH 05/14] sched,rt: Convert switched_{from,to}_rt() / prio_changed_rt() to balance callbacks Peter Zijlstra
2015-06-05 8:48 ` [PATCH 06/14] sched,dl: Remove return value from pull_dl_task() Peter Zijlstra
2015-06-05 8:48 ` [PATCH 07/14] sched,dl: Convert switched_{from,to}_dl() / prio_changed_dl() to balance callbacks Peter Zijlstra
2015-06-05 8:48 ` [PATCH 08/14] hrtimer: Allow hrtimer::function() to free the timer Peter Zijlstra
2015-06-05 9:48 ` Thomas Gleixner
2015-06-07 19:43 ` Oleg Nesterov
2015-06-07 22:33 ` Oleg Nesterov
2015-06-07 22:56 ` Oleg Nesterov
2015-06-08 8:06 ` Thomas Gleixner
2015-06-08 9:14 ` Peter Zijlstra
2015-06-08 10:55 ` Peter Zijlstra [this message]
2015-06-08 12:42 ` Peter Zijlstra
2015-06-08 14:27 ` Oleg Nesterov
2015-06-08 14:42 ` Peter Zijlstra
2015-06-08 15:49 ` Oleg Nesterov
2015-06-08 15:10 ` Peter Zijlstra
2015-06-08 15:16 ` Oleg Nesterov
2015-06-09 21:33 ` Oleg Nesterov
2015-06-09 21:39 ` Oleg Nesterov
2015-06-10 6:55 ` Peter Zijlstra
2015-06-10 7:46 ` Kirill Tkhai
2015-06-10 16:04 ` Oleg Nesterov
2015-06-11 7:31 ` Peter Zijlstra
2015-06-11 16:25 ` Kirill Tkhai
2015-06-10 15:49 ` Oleg Nesterov
2015-06-10 22:37 ` Peter Zijlstra
2015-06-08 14:03 ` Oleg Nesterov
2015-06-08 14:17 ` Peter Zijlstra
2015-06-08 15:10 ` [PATCH 0/3] hrtimer: HRTIMER_STATE_ fixes Oleg Nesterov
2015-06-08 15:11 ` [PATCH 2/3] hrtimer: turn newstate arg of __remove_hrtimer() into clear_enqueued Oleg Nesterov
2015-06-08 15:11 ` [PATCH 3/3] hrtimer: fix the __hrtimer_start_range_ns() race with hrtimer_active() Oleg Nesterov
2015-06-08 15:12 ` [PATCH 1/3] hrtimer: kill HRTIMER_STATE_MIGRATE, fix the race with hrtimer_is_queued() Oleg Nesterov
2015-06-08 15:35 ` [PATCH 0/3] hrtimer: HRTIMER_STATE_ fixes Peter Zijlstra
2015-06-08 15:56 ` Oleg Nesterov
2015-06-08 17:11 ` Thomas Gleixner
2015-06-08 19:08 ` Peter Zijlstra
2015-06-08 20:52 ` Oleg Nesterov
2015-06-08 15:10 ` [PATCH 1/3] hrtimer: kill HRTIMER_STATE_MIGRATE, fix the race with hrtimer_is_queued() Oleg Nesterov
2015-06-08 15:13 ` Oleg Nesterov
2015-06-05 8:48 ` [PATCH 09/14] sched,dl: Fix sched class hopping CBS hole Peter Zijlstra
2015-06-05 8:48 ` [PATCH 10/14] sched: Move code around Peter Zijlstra
2015-06-05 8:48 ` [PATCH 11/14] sched: Streamline the task migration locking a little Peter Zijlstra
2015-06-05 8:48 ` [PATCH 12/14] lockdep: Simplify lock_release() Peter Zijlstra
2015-06-05 8:48 ` [PATCH 13/14] lockdep: Implement lock pinning Peter Zijlstra
2015-06-05 9:55 ` Ingo Molnar
2015-06-11 11:37 ` Peter Zijlstra
2015-06-05 8:48 ` [PATCH 14/14] sched,lockdep: Employ " Peter Zijlstra
2015-06-05 9:57 ` Ingo Molnar
2015-06-05 11:03 ` Peter Zijlstra
2015-06-05 11:24 ` Ingo Molnar
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