s390/pai: fix sampling event removal for PMU device driver

In case of a sampling event, the PAI PMU device drivers need a
reference to this event.  Currently to PMU device driver reference
is removed when a sampling event is destroyed. This may lead to
situations where the reference of the PMU device driver is removed
while being used by a different sampling event.
Reset the event reference pointer of the PMU device driver when
a sampling event is deleted and before the next one might be added.

Fixes: 39d62336 ("s390/pai: add support for cryptography counters")
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Acked-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/kernel/perf_pai_crypto.c

@@ -90,7 +90,6 @@ static void paicrypt_event_destroy(struct perf_event *event)
 						 event->cpu);
 	struct paicrypt_map *cpump = mp->mapptr;
 
-	cpump->event = NULL;
 	static_branch_dec(&pai_key);
 	mutex_lock(&pai_reserve_mutex);
 	debug_sprintf_event(cfm_dbg, 5, "%s event %#llx cpu %d users %d"
@@ -356,10 +355,15 @@ static int paicrypt_add(struct perf_event *event, int flags)
 
 static void paicrypt_stop(struct perf_event *event, int flags)
 {
-	if (!event->attr.sample_period)	/* Counting */
+	struct paicrypt_mapptr *mp = this_cpu_ptr(paicrypt_root.mapptr);
+	struct paicrypt_map *cpump = mp->mapptr;
+
+	if (!event->attr.sample_period) {	/* Counting */
 		paicrypt_read(event);
-	else				/* Sampling */
+	} else {				/* Sampling */
 		perf_sched_cb_dec(event->pmu);
+		cpump->event = NULL;
+	}
 	event->hw.state = PERF_HES_STOPPED;
 }
 

arch/s390/kernel/perf_pai_ext.c

@@ -122,7 +122,6 @@ static void paiext_event_destroy(struct perf_event *event)
 
 	free_page(PAI_SAVE_AREA(event));
 	mutex_lock(&paiext_reserve_mutex);
-	cpump->event = NULL;
 	if (refcount_dec_and_test(&cpump->refcnt))	/* Last reference gone */
 		paiext_free(mp);
 	paiext_root_free();
@@ -362,10 +361,15 @@ static int paiext_add(struct perf_event *event, int flags)
 
 static void paiext_stop(struct perf_event *event, int flags)
 {
-	if (!event->attr.sample_period)	/* Counting */
+	struct paiext_mapptr *mp = this_cpu_ptr(paiext_root.mapptr);
+	struct paiext_map *cpump = mp->mapptr;
+
+	if (!event->attr.sample_period) {	/* Counting */
 		paiext_read(event);
-	else				/* Sampling */
+	} else {				/* Sampling */
 		perf_sched_cb_dec(event->pmu);
+		cpump->event = NULL;
+	}
 	event->hw.state = PERF_HES_STOPPED;
 }