Patch "perf/core: Fix hardlockup failure caused by perf throttle" has been added to the 4.19-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    perf/core: Fix hardlockup failure caused by perf throttle

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     perf-core-fix-hardlockup-failure-caused-by-perf-thro.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 86ab10cb20a0278f39eda74d4c6b792c07b1a38c
Author: Yang Jihong <yangjihong1@xxxxxxxxxx>
Date:   Mon Feb 27 10:35:08 2023 +0800

    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@xxxxxxxxxx>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
    Link: https://lkml.kernel.org/r/20230227023508.102230-1-yangjihong1@xxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 72ed3f3d078fc..2bf4b6b109bf4 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -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;