perf/core: Remove perf_cpu_context::unique_pmu

cpuctx->unique_pmu was originally introduced as a way to identify cpuctxs
with shared pmus in order to avoid visiting the same cpuctx more than once
in a for_each_pmu loop.

cpuctx->unique_pmu == cpuctx->pmu in non-software task contexts since they
have only one pmu per cpuctx. Since perf_pmu_sched_task() is only called in
hw contexts, this patch replaces cpuctx->unique_pmu by cpuctx->pmu in it.

The change above, together with the previous patch in this series, removed
the remaining uses of cpuctx->unique_pmu, so we remove it altogether.

Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vikas Shivappa <vikas.shivappa@linux.intel.com>
Cc: Vince Weaver <vince@deater.net>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/20170118192454.58008-3-davidcc@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/perf_event.h

@@ -785,7 +785,6 @@ struct perf_cpu_context {
 	ktime_t				hrtimer_interval;
 	unsigned int			hrtimer_active;
 
-	struct pmu			*unique_pmu;
 #ifdef CONFIG_CGROUP_PERF
 	struct perf_cgroup		*cgrp;
 	struct list_head		cgrp_cpuctx_entry;

kernel/events/core.c

@@ -2932,7 +2932,7 @@ static void perf_pmu_sched_task(struct task_struct *prev,
 		return;
 
 	list_for_each_entry(cpuctx, this_cpu_ptr(&sched_cb_list), sched_cb_entry) {
-		pmu = cpuctx->unique_pmu; /* software PMUs will not have sched_task */
+		pmu = cpuctx->ctx.pmu; /* software PMUs will not have sched_task */
 
 		if (WARN_ON_ONCE(!pmu->sched_task))
 			continue;
@@ -8636,37 +8636,10 @@ static struct perf_cpu_context __percpu *find_pmu_context(int ctxn)
 	return NULL;
 }
 
-static void update_pmu_context(struct pmu *pmu, struct pmu *old_pmu)
-{
-	int cpu;
-
-	for_each_possible_cpu(cpu) {
-		struct perf_cpu_context *cpuctx;
-
-		cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu);
-
-		if (cpuctx->unique_pmu == old_pmu)
-			cpuctx->unique_pmu = pmu;
-	}
-}
-
 static void free_pmu_context(struct pmu *pmu)
 {
-	struct pmu *i;
-
 	mutex_lock(&pmus_lock);
-	/*
-	 * Like a real lame refcount.
-	 */
-	list_for_each_entry(i, &pmus, entry) {
-		if (i->pmu_cpu_context == pmu->pmu_cpu_context) {
-			update_pmu_context(i, pmu);
-			goto out;
-		}
-	}
-
 	free_percpu(pmu->pmu_cpu_context);
-out:
 	mutex_unlock(&pmus_lock);
 }
 
@@ -8870,8 +8843,6 @@ skip_type:
 		cpuctx->ctx.pmu = pmu;
 
 		__perf_mux_hrtimer_init(cpuctx, cpu);
-
-		cpuctx->unique_pmu = pmu;
 	}
 
 got_cpu_context: