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>

include/linux/init_task.h

@@ -113,6 +113,14 @@ extern struct group_info init_groups;
 # define CAP_INIT_BSET  CAP_INIT_EFF_SET
 #endif
 
+#ifdef CONFIG_PERF_COUNTERS
+# define INIT_PERF_COUNTERS(tsk)					\
+	.perf_counter_ctx.counter_list =				\
+		LIST_HEAD_INIT(tsk.perf_counter_ctx.counter_list),
+#else
+# define INIT_PERF_COUNTERS(tsk)
+#endif
+
 /*
  *  INIT_TASK is used to set up the first task table, touch at
  * your own risk!. Base=0, limit=0x1fffff (=2MB)
@@ -180,6 +188,7 @@ extern struct group_info init_groups;
 	INIT_IDS							\
 	INIT_TRACE_IRQFLAGS						\
 	INIT_LOCKDEP							\
+	INIT_PERF_COUNTERS(tsk)						\
 }
 
 

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;