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)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Thu, 11 May 2023 14:03:31 +0000 (23:03 +0900)
commit2d44928903ed35233a4a5a133a60962770b76835
tree0f6fd10c02ff53bb8f2d36a9bebdeaf1dd5fb962
parent944465c772fb00509150ba374298d9e4d5d47788
perf/core: Fix hardlockup failure caused by perf throttle

[ Upstream commit 15def34e2635ab7e0e96f1bc32e1b69609f14942 ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>
kernel/events/core.c