perf_counter, x86: Make NMI lockups more robust

We have a debug check that detects stuck NMIs and returns with
the PMU disabled in the global ctrl MSR - but i managed to trigger
a situation where this was not enough to deassert the NMI.

So clear/reset the full PMU and keep the disable count balanced when
exiting from here. This way the box produces a debug warning but
stays up and is more debuggable.

[ Impact: in case of PMU related bugs, recover more gracefully ]

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Kacur <jkacur@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index ece3813c7a3c8a58d3d8d08ef76510dac30cfac6..2eeaa99add1c7006ce4ba70665a095004e21607e 100644 (file)
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -724,6 +724,30 @@ static void intel_pmu_save_and_restart(struct perf_counter *counter)
                intel_pmu_enable_counter(hwc, idx);
 }
 
+static void intel_pmu_reset(void)
+{
+       unsigned long flags;
+       int idx;
+
+       if (!x86_pmu.num_counters)
+               return;
+
+       local_irq_save(flags);
+
+       printk("clearing PMU state on CPU#%d\n", smp_processor_id());
+
+       for (idx = 0; idx < x86_pmu.num_counters; idx++) {
+               checking_wrmsrl(x86_pmu.eventsel + idx, 0ull);
+               checking_wrmsrl(x86_pmu.perfctr  + idx, 0ull);
+       }
+       for (idx = 0; idx < x86_pmu.num_counters_fixed; idx++) {
+               checking_wrmsrl(MSR_ARCH_PERFMON_FIXED_CTR0 + idx, 0ull);
+       }
+
+       local_irq_restore(flags);
+}
+
+
 /*
  * This handler is triggered by the local APIC, so the APIC IRQ handling
  * rules apply:
@@ -750,6 +774,8 @@ again:
        if (++loops > 100) {
                WARN_ONCE(1, "perfcounters: irq loop stuck!\n");
                perf_counter_print_debug();
+               intel_pmu_reset();
+               perf_enable();
                return 1;
        }