Messages in this thread | | | Date | Thu, 4 Jun 2015 12:58:55 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 8/9] hrtimer: Allow hrtimer::function() to free the timer |
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On Thu, Jun 04, 2015 at 12:55:37PM +0200, Peter Zijlstra wrote: > On Thu, Jun 04, 2015 at 12:49:02PM +0200, Peter Zijlstra wrote: > > Needs more comments at the very least, its fully of trickery. > > > > @@ -1118,10 +1125,16 @@ static void __run_hrtimer(struct hrtimer > > enum hrtimer_restart (*fn)(struct hrtimer *); > > int restart; > > > > - WARN_ON(!irqs_disabled()); > > + lockdep_assert_held(&cpu_base->lock); > > > > debug_deactivate(timer); > > - base->running = timer; > > + cpu_base->running = timer; > > + > > + /* > > + * separate the ->running assignment from the ->state assignment > > + */ > > + write_seqcount_begin(&cpu_base->seq); > > Maybe these need to be raw_write_seqcount_latch()..
I'm properly confusing my self, so let me write a little more detail;
I didn't think it needed the double wmb because:
[S] running = timer; [S] seq++; WMB [S] state = INACTIVE
I don't think it matters if we re-order the first two stores, since at that point ->state is still ENQUEUED and we're good.
Similar for the case below, you can flip the seq increment and the ->running clear, but at that time ->state should already be ENQUEUED again (if indeed the timer got re-armed), otherwise its not active anymore.
> > __remove_hrtimer(timer, base, HRTIMER_STATE_INACTIVE, 0); > > timer_stats_account_hrtimer(timer); > > fn = timer->function; > > @@ -1150,8 +1163,13 @@ static void __run_hrtimer(struct hrtimer > > !(timer->state & HRTIMER_STATE_ENQUEUED)) > > enqueue_hrtimer(timer, base); > > > > - WARN_ON_ONCE(base->running != timer); > > - base->running = NULL; > > + /* > > + * separate the ->running assignment from the ->state assignment > > + */ > > + write_seqcount_end(&cpu_base->seq); > > + > > + WARN_ON_ONCE(cpu_base->running != timer); > > + cpu_base->running = NULL; > > } > > > > static void __hrtimer_run_queues(struct hrtimer_cpu_base *cpu_base, ktime_t now)
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