Commit 6805c1fc authored Feb 27, 2023 by Yang Jihong Committed by Greg Kroah-Hartman May 17, 2023

perf/core: Fix hardlockup failure caused by perf throttle



[ Upstream commit 15def34e2635ab7e0e96f1bc32e1b69609f14942 ]

commit e050e3f0 ("perf: Fix broken interrupt rate throttling")
introduces a change in throttling threshold judgment. Before this,
compare hwc->interrupts and max_samples_per_tick, then increase
hwc->interrupts by 1, but this commit reverses order of these two
behaviors, causing the semantics of max_samples_per_tick to change.
In literal sense of "max_samples_per_tick", if hwc->interrupts ==
max_samples_per_tick, it should not be throttled, therefore, the judgment
condition should be changed to "hwc->interrupts > max_samples_per_tick".

In fact, this may cause the hardlockup to fail, The minimum value of
max_samples_per_tick may be 1, in this case, the return value of
__perf_event_account_interrupt function is 1.
As a result, nmi_watchdog gets throttled, which would stop PMU (Use x86
architecture as an example, see x86_pmu_handle_irq).

Fixes: e050e3f0 ("perf: Fix broken interrupt rate throttling")
Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20230227023508.102230-1-yangjihong1@huawei.com


Signed-off-by: Sasha Levin <sashal@kernel.org>

parent c5a65267

kernel/events/core.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -7843,8 +7843,8 @@ __perf_event_account_interrupt(struct perf_event *event, int throttle)
		hwc->interrupts = 1;
		} else {
		hwc->interrupts++;
		if (unlikely(throttle
		&& hwc->interrupts >= max_samples_per_tick)) {
		if (unlikely(throttle &&
		hwc->interrupts > max_samples_per_tick)) {
		__this_cpu_inc(perf_throttled_count);
		tick_dep_set_cpu(smp_processor_id(), TICK_DEP_BIT_PERF_EVENTS);
		hwc->interrupts = MAX_INTERRUPTS;