[PATCH 09/12] perf: Fix scaling vs enable_on_exec

[Peter Zijlstra]

The recent commit 3e349507d12d ("perf: Fix perf_enable_on_exec() event
scheduling") caused this by moving task_ctx_sched_out() from before
__perf_event_mask_enable() to after it.

The overlooked concequence of that change is that task_ctx_sched_out()
would update the ctx time fields, and now __perf_event_mask_enable()
uses stale time.

In order to fix this, explicitly stop our context's time before
enabling the event(s).

Fixes: 3e349507d12d ("perf: Fix perf_enable_on_exec() event scheduling")
Reported-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/events/core.c |    1 +
 1 file changed, 1 insertion(+)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3143,6 +3143,7 @@ static void perf_event_enable_on_exec(in
 
 	cpuctx = __get_cpu_context(ctx);
 	perf_ctx_lock(cpuctx, ctx);
+	ctx_sched_out(ctx, cpuctx, EVENT_TIME);
 	list_for_each_entry(event, &ctx->event_list, event_entry)
 		enabled |= event_enable_on_exec(event, ctx);