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authorFrederic Weisbecker <frederic@kernel.org>2021-07-26 15:55:13 +0300
committerThomas Gleixner <tglx@linutronix.de>2021-08-10 18:09:59 +0300
commitee375328f579f94251eb66d5dc91aba056019a31 (patch)
treed6179c3dd82cd1ff6e8719da707a35ae9506d403 /include/linux/posix-timers.h
parent5c8f23e6b73c13d9f7b52614783dcb9169883296 (diff)
downloadlinux-ee375328f579f94251eb66d5dc91aba056019a31.tar.xz
posix-cpu-timers: Recalc next expiration when timer_settime() ends up not queueing
There are several scenarios that can result in posix_cpu_timer_set() not queueing the timer but still leaving the threadgroup cputime counter running or keeping the tick dependency around for a random amount of time. 1) If timer_settime() is called with a 0 expiration on a timer that is already disabled, the process wide cputime counter will be started and won't ever get a chance to be stopped by stop_process_timer() since no timer is actually armed to be processed. The following snippet is enough to trigger the issue. void trigger_process_counter(void) { timer_t id; struct itimerspec val = { }; timer_create(CLOCK_PROCESS_CPUTIME_ID, NULL, &id); timer_settime(id, TIMER_ABSTIME, &val, NULL); timer_delete(id); } 2) If timer_settime() is called with a 0 expiration on a timer that is already armed, the timer is dequeued but not really disarmed. So the process wide cputime counter and the tick dependency may still remain a while around. The following code snippet keeps this overhead around for one week after the timer deletion: void trigger_process_counter(void) { timer_t id; struct itimerspec val = { }; val.it_value.tv_sec = 604800; timer_create(CLOCK_PROCESS_CPUTIME_ID, NULL, &id); timer_settime(id, 0, &val, NULL); timer_delete(id); } 3) If the timer was initially deactivated, this call to timer_settime() with an early expiration may have started the process wide cputime counter even though the timer hasn't been queued and armed because it has fired early and inline within posix_cpu_timer_set() itself. As a result the process wide cputime counter may never stop until a new timer is ever armed in the future. The following code snippet can reproduce this: void trigger_process_counter(void) { timer_t id; struct itimerspec val = { }; signal(SIGALRM, SIG_IGN); timer_create(CLOCK_PROCESS_CPUTIME_ID, NULL, &id); val.it_value.tv_nsec = 1; timer_settime(id, TIMER_ABSTIME, &val, NULL); } 4) If the timer was initially armed with a former expiration value before this call to timer_settime() and the current call sets an early deadline that has already expired, the timer fires inline within posix_cpu_timer_set(). In this case it must have been dequeued before firing inline with its new expiration value, yet it hasn't been disarmed in this case. So the process wide cputime counter and the tick dependency may still be around for a while even after the timer fired. The following code snippet can reproduce this: void trigger_process_counter(void) { timer_t id; struct itimerspec val = { }; signal(SIGALRM, SIG_IGN); timer_create(CLOCK_PROCESS_CPUTIME_ID, NULL, &id); val.it_value.tv_sec = 100; timer_settime(id, TIMER_ABSTIME, &val, NULL); val.it_value.tv_sec = 0; val.it_value.tv_nsec = 1; timer_settime(id, TIMER_ABSTIME, &val, NULL); } Fix all these issues with triggering the related base next expiration recalculation on the next tick. This also implies to re-evaluate the need to keep around the process wide cputime counter and the tick dependency, in a similar fashion to disarm_timer(). Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20210726125513.271824-7-frederic@kernel.org
Diffstat (limited to 'include/linux/posix-timers.h')
-rw-r--r--include/linux/posix-timers.h7
1 files changed, 6 insertions, 1 deletions
diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index 4cf1fbe8d1bc..00fef0064355 100644
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -82,9 +82,14 @@ static inline bool cpu_timer_enqueue(struct timerqueue_head *head,
return timerqueue_add(head, &ctmr->node);
}
+static inline bool cpu_timer_queued(struct cpu_timer *ctmr)
+{
+ return !!ctmr->head;
+}
+
static inline bool cpu_timer_dequeue(struct cpu_timer *ctmr)
{
- if (ctmr->head) {
+ if (cpu_timer_queued(ctmr)) {
timerqueue_del(ctmr->head, &ctmr->node);
ctmr->head = NULL;
return true;