perfcounters: pull inherited counters

Change counter inheritance from a 'push' to a 'pull' model: instead of
child tasks pushing their final counts to the parent, reuse the wait4
infrastructure to pull counters as child tasks are exit-processed,
much like how cutime/cstime is collected.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 9 insertions, 12 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 244edfd..101b7ee 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -153,6 +153,9 @@ static void delayed_put_task_struct(struct rcu_head *rhp)
 {
 	struct task_struct *tsk = container_of(rhp, struct task_struct, rcu);
 
+#ifdef CONFIG_PERF_COUNTERS
+	WARN_ON_ONCE(!list_empty(&tsk->perf_counter_ctx.counter_list));
+#endif
 	trace_sched_process_free(tsk);
 	put_task_struct(tsk);
 }
@@ -922,12 +925,6 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
 	forget_original_parent(tsk);
 	exit_task_namespaces(tsk);
 
-	/*
-	 * Flush inherited counters to the parent - before the parent
-	 * gets woken up by child-exit notifications.
-	 */
-	perf_counter_exit_task(tsk);
-
 	write_lock_irq(&tasklist_lock);
 	if (group_dead)
 		kill_orphaned_pgrp(tsk->group_leader, NULL);
@@ -1122,12 +1119,6 @@ NORET_TYPE void do_exit(long code)
 	if (tsk->splice_pipe)
 		__free_pipe_info(tsk->splice_pipe);
 
-	/*
-	 * These must happen late, after the PID is not
-	 * hashed anymore, but still at a point that may sleep:
-	 */
-	perf_counter_exit_task(tsk);
-
 	preempt_disable();
 	/* causes final put_task_struct in finish_task_switch(). */
 	tsk->state = TASK_DEAD;
@@ -1371,6 +1362,12 @@ static int wait_task_zombie(struct task_struct *p, int options,
 	 */
 	read_unlock(&tasklist_lock);
 
+	/*
+	 * Flush inherited counters to the parent - before the parent
+	 * gets woken up by child-exit notifications.
+	 */
+	perf_counter_exit_task(p);
+
 	retval = ru ? getrusage(p, RUSAGE_BOTH, ru) : 0;
 	status = (p->signal->flags & SIGNAL_GROUP_EXIT)
 		? p->signal->group_exit_code : p->exit_code;