From fa34295619755c02442a53e742dbf3ebb384f30d Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Tue, 25 Sep 2018 17:58:35 +0200
Subject: [PATCH] perf/core: Fix perf_pmu_unregister() locking

commit a9f9772114c8b07ae75bcb3654bd017461248095 upstream.

When we unregister a PMU, we fail to serialize the @pmu_idr properly.
Fix that by doing the entire thing under pmu_lock.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Fixes: 2e80a82a49c4 ("perf: Dynamic pmu types")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[bwh: Backported to 3.16:
 - Also remove "out" label in free_pmu_context()
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 kernel/events/core.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index f23a497d47e2..5f3f1a45c73a 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6419,20 +6419,17 @@ 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;
+			return;
 		}
 	}
 
 	free_percpu(pmu->pmu_cpu_context);
-out:
-	mutex_unlock(&pmus_lock);
 }
 static struct idr pmu_idr;
 
@@ -6593,12 +6590,8 @@ free_pdc:
 
 void perf_pmu_unregister(struct pmu *pmu)
 {
-	int remove_device;
-
 	mutex_lock(&pmus_lock);
-	remove_device = pmu_bus_running;
 	list_del_rcu(&pmu->entry);
-	mutex_unlock(&pmus_lock);
 
 	/*
 	 * We dereference the pmu list under both SRCU and regular RCU, so
@@ -6610,11 +6603,12 @@ void perf_pmu_unregister(struct pmu *pmu)
 	free_percpu(pmu->pmu_disable_count);
 	if (pmu->type >= PERF_TYPE_MAX)
 		idr_remove(&pmu_idr, pmu->type);
-	if (remove_device) {
+	if (pmu_bus_running) {
 		device_del(pmu->dev);
 		put_device(pmu->dev);
 	}
 	free_pmu_context(pmu);
+	mutex_unlock(&pmus_lock);
 }
 
 struct pmu *perf_init_event(struct perf_event *event)