• Yang Jihong's avatar
    perf/core: Fix hardlockup failure caused by perf throttle · 15def34e
    Yang Jihong authored
    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: default avatarYang Jihong <yangjihong1@huawei.com>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Link: https://lkml.kernel.org/r/20230227023508.102230-1-yangjihong1@huawei.com
    15def34e
core.c 330 KB