perf/core: Fix hardlockup failure caused by perf throttle
[ Upstream commit15def34e26
] commite050e3f0a7
("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:e050e3f0a7
("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>
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@ -9254,8 +9254,8 @@ __perf_event_account_interrupt(struct perf_event *event, int throttle)
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hwc->interrupts = 1;
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hwc->interrupts = 1;
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} else {
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} else {
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hwc->interrupts++;
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hwc->interrupts++;
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if (unlikely(throttle
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if (unlikely(throttle &&
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&& hwc->interrupts >= max_samples_per_tick)) {
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hwc->interrupts > max_samples_per_tick)) {
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__this_cpu_inc(perf_throttled_count);
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__this_cpu_inc(perf_throttled_count);
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tick_dep_set_cpu(smp_processor_id(), TICK_DEP_BIT_PERF_EVENTS);
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tick_dep_set_cpu(smp_processor_id(), TICK_DEP_BIT_PERF_EVENTS);
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hwc->interrupts = MAX_INTERRUPTS;
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hwc->interrupts = MAX_INTERRUPTS;
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