Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net

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

diff --git a/kernel/events/core.c b/kernel/events/core.c
index a7b8c1c..9fc3be0 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2496,11 +2496,11 @@ 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;
 
@@ -3549,10 +3549,18 @@ static int perf_event_read(struct perf_event *event, bool group)
                        .group = group,
                        .ret = 0,
                };
-               ret = smp_call_function_single(event->oncpu, __perf_event_read, &data, 1);
-               /* The event must have been read from an online CPU: */
-               WARN_ON_ONCE(ret);
-               ret = ret ? : data.ret;
+               /*
+                * Purposely ignore the smp_call_function_single() return
+                * value.
+                *
+                * If event->oncpu isn't a valid CPU it means the event got
+                * scheduled out and that will have updated the event count.
+                *
+                * Therefore, either way, we'll have an up-to-date event count
+                * after this.
+                */
+               (void)smp_call_function_single(event->oncpu, __perf_event_read, &data, 1);
+               ret = data.ret;
        } else if (event->state == PERF_EVENT_STATE_INACTIVE) {
                struct perf_event_context *ctx = event->ctx;
                unsigned long flags;
@@ -4837,6 +4845,19 @@ 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) {
@@ -6112,7 +6133,7 @@ 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)
@@ -6156,7 +6177,13 @@ 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);
@@ -6670,7 +6697,7 @@ 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);
 }
 
 /*
@@ -7933,7 +7960,7 @@ static void perf_event_addr_filters_apply(struct perf_event *event)
        mmput(mm);
 
 restart:
-       perf_event_restart(event);
+       perf_event_stop(event, 1);
 }
 
 /*