Merge branch 'perf/urgent' into perf/core, to pick up fixes

[cascardo/linux.git] / kernel / events / core.c

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 74f22a9..fedba31 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2497,11 +2497,11 @@ static int __perf_event_stop(void *info)
        return 0;
 }
 
-static int perf_event_restart(struct perf_event *event)
+static int perf_event_stop(struct perf_event *event, int restart)
 {
        struct stop_event_data sd = {
                .event          = event,
-               .restart        = 1,
+               .restart        = restart,
        };
        int ret = 0;
 
@@ -4874,6 +4874,19 @@ static void ring_buffer_attach(struct perf_event *event,
                spin_unlock_irqrestore(&rb->event_lock, flags);
        }
 
+       /*
+        * Avoid racing with perf_mmap_close(AUX): stop the event
+        * before swizzling the event::rb pointer; if it's getting
+        * unmapped, its aux_mmap_count will be 0 and it won't
+        * restart. See the comment in __perf_pmu_output_stop().
+        *
+        * Data will inevitably be lost when set_output is done in
+        * mid-air, but then again, whoever does it like this is
+        * not in for the data anyway.
+        */
+       if (has_aux(event))
+               perf_event_stop(event, 0);
+
        rcu_assign_pointer(event->rb, rb);
 
        if (old_rb) {
@@ -6150,7 +6163,7 @@ static void perf_event_addr_filters_exec(struct perf_event *event, void *data)
        raw_spin_unlock_irqrestore(&ifh->lock, flags);
 
        if (restart)
-               perf_event_restart(event);
+               perf_event_stop(event, 1);
 }
 
 void perf_event_exec(void)
@@ -6194,7 +6207,13 @@ static void __perf_event_output_stop(struct perf_event *event, void *data)
 
        /*
         * In case of inheritance, it will be the parent that links to the
-        * ring-buffer, but it will be the child that's actually using it:
+        * ring-buffer, but it will be the child that's actually using it.
+        *
+        * We are using event::rb to determine if the event should be stopped,
+        * however this may race with ring_buffer_attach() (through set_output),
+        * which will make us skip the event that actually needs to be stopped.
+        * So ring_buffer_attach() has to stop an aux event before re-assigning
+        * its rb pointer.
         */
        if (rcu_dereference(parent->rb) == rb)
                ro->err = __perf_event_stop(&sd);
@@ -6708,7 +6727,7 @@ static void __perf_addr_filters_adjust(struct perf_event *event, void *data)
        raw_spin_unlock_irqrestore(&ifh->lock, flags);
 
        if (restart)
-               perf_event_restart(event);
+               perf_event_stop(event, 1);
 }
 
 /*
@@ -7897,7 +7916,7 @@ static void perf_event_addr_filters_apply(struct perf_event *event)
        mmput(mm);
 
 restart:
-       perf_event_restart(event);
+       perf_event_stop(event, 1);
 }
 
 /*