tick/broadcast: Serialize access to tick_next_period (f73f64d5) · Commits · 戴 / test

tick_broadcast_setup_oneshot() accesses tick_next_period twice without any serialization. This is wrong in two aspects: - Reading it twice might make the broadcast data inconsistent if the variable is updated concurrently. - On 32bit systems the access might see an partial update Protect it with jiffies_lock. That's safe as none of the callchains leading up to this function can create a lock ordering violation: timer interrupt run_local_timers() hrtimer_run_queues() hrtimer_switch_to_hres() tick_init_highres() tick_switch_to_oneshot() tick_broadcast_switch_to_oneshot() or tick_check_oneshot_change() tick_nohz_switch_to_nohz() tick_switch_to_oneshot() tick_broadcast_switch_to_oneshot() Signed-off-by:

Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20201117132006.061341507@linutronix.de

kernel/time/tick-broadcast.c

+20 −3

Original line number	Diff line number	Diff line
		@@ -877,6 +877,22 @@ static void tick_broadcast_init_next_event(struct cpumask *mask,
		}
		}

		static inline ktime_t tick_get_next_period(void)
		{
		ktime_t next;

		/*
		* Protect against concurrent updates (store /load tearing on
		* 32bit). It does not matter if the time is already in the
		* past. The broadcast device which is about to be programmed will
		* fire in any case.
		*/
		raw_spin_lock(&jiffies_lock);
		next = tick_next_period;
		raw_spin_unlock(&jiffies_lock);
		return next;
		}

		/**
		* tick_broadcast_setup_oneshot - setup the broadcast device
		*/
		@@ -905,10 +921,11 @@ static void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
		tick_broadcast_oneshot_mask, tmpmask);

		if (was_periodic && !cpumask_empty(tmpmask)) {
		ktime_t nextevt = tick_get_next_period();

		clockevents_switch_state(bc, CLOCK_EVT_STATE_ONESHOT);
		tick_broadcast_init_next_event(tmpmask,
		tick_next_period);
		tick_broadcast_set_event(bc, cpu, tick_next_period);
		tick_broadcast_init_next_event(tmpmask, nextevt);
		tick_broadcast_set_event(bc, cpu, nextevt);
		} else
		bc->next_event = KTIME_MAX;
		} else {

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