perf/core: Fix hardlockup failure caused by perf throttle
authorYang Jihong <yangjihong1@huawei.com>
Mon, 27 Feb 2023 02:35:08 +0000 (10:35 +0800)
committerPeter Zijlstra <peterz@infradead.org>
Fri, 14 Apr 2023 14:08:22 +0000 (16:08 +0200)
commit15def34e2635ab7e0e96f1bc32e1b69609f14942
tree6f5eed1a6bf23dca68381cb036c35a57b208010d
parent872d28001be56b205bd9b3f97cea1571a1bde317
perf/core: Fix hardlockup failure caused by perf throttle

commit e050e3f0a71bf ("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: e050e3f0a71b ("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
kernel/events/core.c