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Commit 4fe757dd authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

perf: Fix throttle logic 



It was possible to call pmu::start() on an already running event. In
particular this lead so some wreckage as the hrtimer events would
re-initialize active timers.

This was due to throttled events being activated again by scheduling.
Scheduling in a context would add and force start events, resulting in
running events with a possible throttle status. The next tick to hit
that task will then try to unthrottle the event and call ->start() on
an already running event.

Reported-by: default avatarJeff Moyer <jmoyer@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 7d44ec19

kernel/perf_event.c

+15 −4
Original line number Diff line number Diff line
@@ -782,6 +782,10 @@ void perf_event_disable(struct perf_event *event) 
	raw_spin_unlock_irq(&ctx->lock);

}



#define MAX_INTERRUPTS (~0ULL)



static void perf_log_throttle(struct perf_event *event, int enable);



static int

event_sched_in(struct perf_event *event,

		 struct perf_cpu_context *cpuctx,
@@ -794,6 +798,17 @@ event_sched_in(struct perf_event *event, 


	event->state = PERF_EVENT_STATE_ACTIVE;

	event->oncpu = smp_processor_id();



	/*

	 * Unthrottle events, since we scheduled we might have missed several

	 * ticks already, also for a heavily scheduling task there is little

	 * guarantee it'll get a tick in a timely manner.

	 */

	if (unlikely(event->hw.interrupts == MAX_INTERRUPTS)) {

		perf_log_throttle(event, 1);

		event->hw.interrupts = 0;

	}



	/*

	 * The new state must be visible before we turn it on in the hardware:

	 */
@@ -1596,10 +1611,6 @@ void __perf_event_task_sched_in(struct task_struct *task) 
	}

}



#define MAX_INTERRUPTS (~0ULL)



static void perf_log_throttle(struct perf_event *event, int enable);



static u64 perf_calculate_period(struct perf_event *event, u64 nsec, u64 count)

{

	u64 frequency = event->attr.sample_freq;