On Wed, Mar 10, 2021 at 11:41:34AM +0100, Marco Elver wrote:
Adds bit perf_event_attr::remove_on_exec, to support removing an event from a task on exec.
This option supports the case where an event is supposed to be process-wide only, and should not propagate beyond exec, to limit monitoring to the original process image only.
Signed-off-by: Marco Elver elver@google.com
+/*
- Removes all events from the current task that have been marked
- remove-on-exec, and feeds their values back to parent events.
- */
+static void perf_event_remove_on_exec(void) +{
- int ctxn;
- for_each_task_context_nr(ctxn) {
struct perf_event_context *ctx;struct perf_event *event, *next;ctx = perf_pin_task_context(current, ctxn);if (!ctx)continue;mutex_lock(&ctx->mutex);list_for_each_entry_safe(event, next, &ctx->event_list, event_entry) {if (!event->attr.remove_on_exec)continue;if (!is_kernel_event(event))perf_remove_from_owner(event);perf_remove_from_context(event, DETACH_GROUP);
There's a comment on this in perf_event_exit_event(), if this task happens to have the original event, then DETACH_GROUP will destroy the grouping.
I think this wants to be:
perf_remove_from_text(event, child_event->parent ? DETACH_GROUP : 0);
or something.
/** Remove the event and feed back its values to the* parent event.*/perf_event_exit_event(event, ctx, current);
Oooh, and here we call it... but it will do list_del_even() / perf_group_detach() *again*.
So the problem is that perf_event_exit_task_context() doesn't use remove_from_context(), but instead does task_ctx_sched_out() and then relies on the events not being active.
Whereas above you *DO* use remote_from_context(), but then perf_event_exit_event() will try and remove it more.
}mutex_unlock(&ctx->mutex);
perf_unpin_context(ctx);
put_ctx(ctx);- }
+}