perf/x86/intel/pebs: Fix event disable PEBS buffer drain

When disabling a PEBS event, we need to drain the buffer. Doing so
requires a correct cpuc->pebs_active mask.

The current code clears the pebs_active bit before draining the
buffer. Fix that.
Signed-off-by: "Liang, Kan" <kan.liang@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver<vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/37D7C6CF3E00A74B8858931C1DB2F07701885A65@SHSMSX103.ccr.corp.intel.com
[ Fixed the SOB. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/cpu/perf_event_intel_ds.c

@@ -789,6 +789,11 @@ void intel_pmu_pebs_disable(struct perf_event *event)
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
 	struct hw_perf_event *hwc = &event->hw;
 	struct debug_store *ds = cpuc->ds;
+	bool large_pebs = ds->pebs_interrupt_threshold >
+		ds->pebs_buffer_base + x86_pmu.pebs_record_size;
+
+	if (large_pebs)
+		intel_pmu_drain_pebs_buffer();
 
 	cpuc->pebs_enabled &= ~(1ULL << hwc->idx);
 
@@ -797,12 +802,8 @@ void intel_pmu_pebs_disable(struct perf_event *event)
 	else if (event->hw.flags & PERF_X86_EVENT_PEBS_ST)
 		cpuc->pebs_enabled &= ~(1ULL << 63);
 
-	if (ds->pebs_interrupt_threshold >
-	    ds->pebs_buffer_base + x86_pmu.pebs_record_size) {
-		intel_pmu_drain_pebs_buffer();
-		if (!pebs_is_enabled(cpuc))
+	if (large_pebs && !pebs_is_enabled(cpuc))
 		perf_sched_cb_dec(event->ctx->pmu);
-	}
 
 	if (cpuc->enabled)
 		wrmsrl(MSR_IA32_PEBS_ENABLE, cpuc->pebs_enabled);