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authorThomas Gleixner <tglx@linutronix.de>2020-11-17 14:19:43 +0100
committerThomas Gleixner <tglx@linutronix.de>2020-11-19 10:48:28 +0100
commitf73f64d5687192bc8eb7f3d9521ca6256b79f224 (patch)
tree9697fa0581b26217f309095d33fe7cd2a82a0f9e /kernel/time
parent66981c37b3199d293c58f84cf2366e86a06e1a3d (diff)
tick/broadcast: Serialize access to tick_next_period
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
Diffstat (limited to 'kernel/time')
-rw-r--r--kernel/time/tick-broadcast.c23
1 files changed, 20 insertions, 3 deletions
diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 36d7464c8962..2a47c8f80e53 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -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 {