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Subject[PATCH] perf: remove deprecated warn_on_once()

With the new throttling/unthrottling code introduced with
commit e050e3f, we hit two warn_on_once() in:
- intel_pmu_pebs_enable()
- intel_pmu_lbr_enable()

The assertions are no longer problematic. There is a valid
path where they can trigger but it is harmless.

The assertion can be triggered with:
$ perf record -e instructions:pp ....
Leading to paths:

intel_pmu_pebs_enable
intel_pmu_enable_event
x86_perf_event_set_period
x86_pmu_start
perf_adjust_freq_unthr_context
perf_event_task_tick
scheduler_tick

And:

intel_pmu_lbr_enable
intel_pmu_enable_event
x86_perf_event_set_period
x86_pmu_start
perf_adjust_freq_unthr_context.
perf_event_task_tick
scheduler_tick

cpuc->enabled is always on because when we get to
perf_adjust_freq_unthr_context() the PMU is not totally
disabled. Furthermore when we need to adjust a period,
we only stop the event we need to change and not the
entire PMU. Thus, when we re-enable, cpuc->enabled is
already set. Note that when we stop the event, both
pebs and lbr are stopped if necessary (and possible).

Signed-off-by: Stephane Eranian <eranian@google.com>
---
diff --git a/arch/x86/kernel/cpu/perf_event_intel_ds.c b/arch/x86/kernel/cpu/perf_event_intel_ds.c
index 73da6b6..d6bd49f 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_ds.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c
@@ -439,7 +439,6 @@ void intel_pmu_pebs_enable(struct perf_event *event)
hwc->config &= ~ARCH_PERFMON_EVENTSEL_INT;

cpuc->pebs_enabled |= 1ULL << hwc->idx;
- WARN_ON_ONCE(cpuc->enabled);

if (x86_pmu.intel_cap.pebs_trap && event->attr.precise_ip > 1)
intel_pmu_lbr_enable(event);
diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index 3fab3de..47a7e63 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -72,8 +72,6 @@ void intel_pmu_lbr_enable(struct perf_event *event)
if (!x86_pmu.lbr_nr)
return;

- WARN_ON_ONCE(cpuc->enabled);
-
/*
* Reset the LBR stack if we changed task context to
* avoid data leaks.

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