Messages in this thread Patch in this message |  | | Date | Mon, 8 Jun 2015 16:17:09 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 08/14] hrtimer: Allow hrtimer::function() to free the timer |
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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: > > And I think there is a problem. Consider a timer TIMER which always > > rearms itself using some "default" timeout. > > > > In this case __hrtimer_start_range_ns(&TIMER, ...) must preserve > > hrtimer_active(&TIMER) == T. By definition, and currently this is > > true. > > > > After this patch this is no longer true (afaics). If the timer is > > pending but not running, __hrtimer_start_range_ns()->remove_hrtimer() > > will clear ENQUEUED first, then set it again in enqueue_hrtimer(). > > That is so even with the current code; the current code uses: > > hrtimer->state & CALLBACK > > for __remove_hrtimer(.state). In the above case of a pending timer, > that's 0 aka. HRTIMER_STATE_INACTIVE. > > > This means that hrtimer_active() returns false in between. And note > > that it doesn't matter if the timer changes its ->base or not, so > > that 2nd cpu_base above can't help. > > > > I think that __hrtimer_start_range_ns() should preserve ENQUEUED > > like migrate_hrtimer_list() should do (see the previous email). > > I tend to agree, but I think its a pre-existing problem, not one > introduced by my proposed patch.
Something like this would fix that I think. It fully preserves timer->state over hrtimer_start_range_ns().
--- kernel/time/hrtimer.c | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-)
--- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -891,10 +891,10 @@ static void __remove_hrtimer(struct hrti * remove hrtimer, called with base lock held */ static inline int -remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base) +remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base, bool restart) { if (hrtimer_is_queued(timer)) { - unsigned long state; + unsigned long state = timer->state; int reprogram; /* @@ -908,12 +908,15 @@ remove_hrtimer(struct hrtimer *timer, st debug_deactivate(timer); timer_stats_hrtimer_clear_start_info(timer); reprogram = base->cpu_base == this_cpu_ptr(&hrtimer_bases); - /* - * We must preserve the CALLBACK state flag here, - * otherwise we could move the timer base in - * switch_hrtimer_base. - */ - state = timer->state & HRTIMER_STATE_CALLBACK; + + if (!restart) { + /* + * We must preserve the CALLBACK state flag here, + * otherwise we could move the timer base in + * switch_hrtimer_base. + */ + state &= HRTIMER_STATE_CALLBACK; + } __remove_hrtimer(timer, base, state, reprogram); return 1; } @@ -938,7 +941,7 @@ void hrtimer_start_range_ns(struct hrtim base = lock_hrtimer_base(timer, &flags); /* Remove an active timer from the queue: */ - remove_hrtimer(timer, base); + remove_hrtimer(timer, base, true); if (mode & HRTIMER_MODE_REL) { tim = ktime_add_safe(tim, base->get_time()); @@ -1007,7 +1010,7 @@ int hrtimer_try_to_cancel(struct hrtimer base = lock_hrtimer_base(timer, &flags); if (!hrtimer_callback_running(timer)) - ret = remove_hrtimer(timer, base); + ret = remove_hrtimer(timer, base, false); unlock_hrtimer_base(timer, &flags);
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