On Thu, Jul 04, 2019 at 07:00:18PM +0300, Alexander Shishkin wrote:
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 8cfb721bb284..fc586da37067 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -1887,6 +1887,57 @@ list_del_event(struct perf_event *event, struct
> perf_event_context *ctx)
> ctx->generation++;
> }
>
> +static int
> +perf_aux_source_match(struct perf_event *event, struct perf_event *aux_event)
> +{
> + if (!has_aux(aux_event))
> + return 0;
> +
> + if (!event->pmu->aux_source_match)
> + return 0;
> +
> + return event->pmu->aux_source_match(aux_event);
> +}
> +
> +static void put_event(struct perf_event *event);
> +static void event_sched_out(struct perf_event *event,
> + struct perf_cpu_context *cpuctx,
> + struct perf_event_context *ctx);
> +
> +static void perf_put_aux_event(struct perf_event *event)
> +{
> + struct perf_event_context *ctx = event->ctx;
> + struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
> + struct perf_event *iter = NULL;
> +
> + /*
> + * If event uses aux_event tear down the link
> + */
> + if (event->aux_event) {
> + put_event(event->aux_event);
> + event->aux_event = NULL;
> + return;
> + }
> +
> + /*
> + * If the event is an aux_event, tear down all links to
> + * it from other events.
> + */
> + for_each_sibling_event(iter, event->group_leader) {
> + if (iter->aux_event != event)
> + continue;
> +
> + iter->aux_event = NULL;
> + put_event(event);
> +
> + /*
> + * If it's ACTIVE, schedule it out. It won't schedule
> + * again because !aux_event.
> + */
> + event_sched_out(iter, cpuctx, ctx);
> + }
> +}
I'm thinking we can use a perf_get_aux_event() to use below.
> +
> static void perf_group_detach(struct perf_event *event)
> {
> struct perf_event *sibling, *tmp;
> @@ -1902,6 +1953,8 @@ static void perf_group_detach(struct perf_event *event)
>
> event->attach_state &= ~PERF_ATTACH_GROUP;
>
> + perf_put_aux_event(event);
> +
> /*
> * If this is a sibling, remove it from its group.
> */
> @@ -10396,6 +10449,12 @@ perf_event_alloc(struct perf_event_attr *attr, int
> cpu,
> goto err_ns;
> }
>
> + if (event->attr.aux_source &&
> + !(pmu->capabilities & PERF_PMU_CAP_AUX_SOURCE)) {
> + err = -EOPNOTSUPP;
> + goto err_pmu;
> + }
> +
> err = exclusive_event_init(event);
> if (err)
> goto err_pmu;
> @@ -11052,6 +11111,39 @@ SYSCALL_DEFINE5(perf_event_open,
> }
> }
>
> + if (event->attr.aux_source) {
> + struct perf_event *aux_event = group_leader;
> +
> + /*
> + * One of the events in the group must be an aux event
> + * if we want to be an aux_source. This way, the aux event
> + * will precede its aux_source events in the group, and
> + * therefore will always schedule first.
Can't we mandate that the group leader is the AUX event?
> + */
> + err = -EINVAL;
> + if (!aux_event)
> + goto err_locked;
> +
> + if (perf_aux_source_match(event, aux_event))
> + goto found_aux;
> +
> + for_each_sibling_event(aux_event, group_leader) {
> + if (perf_aux_source_match(event, aux_event))
> + goto found_aux;
> + }
> +
> + goto err_locked;
> +
> +found_aux:
> + /*
> + * Link aux_sources to their aux event; this is undone in
> + * perf_group_detach(). When the group in torn down, the
> + * aux_source events loose their link to the aux_event and
> + * can't schedule any more.
> + */
> + if (atomic_long_inc_not_zero(&aux_event->refcount))
> + event->aux_event = aux_event;
I'm thinking failing that inc_not_zero() is BAD (tm) ?!
> + }
With the sugggested perf_get_aux_event() this would become something
like:
if (event->attr.aux_source && !perf_get_aux_event(event, group_leader))
goto err_locked;
or something.
>
> /*
> * Must be under the same ctx::mutex as perf_install_in_context(),
> --
> 2.20.1
>
