Revert "perf: Rework perf_event_exit_event()"

This reverts commit 94902ee2996a7f71471138093495df452dab87b6 which is
upstream commit ef54c1a476aef7eef26fe13ea10dc090952c00f8.

Reverting for now due to issues that need to get fixed upstream.

Signed-off-by: Sasha Levin <sashal@kernel.org>

2 files changed, 63 insertions, 80 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index c095e713cf08..ce14fb2772b5 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -607,7 +607,6 @@ struct swevent_hlist {
 #define PERF_ATTACH_TASK_DATA	0x08
 #define PERF_ATTACH_ITRACE	0x10
 #define PERF_ATTACH_SCHED_CB	0x20
-#define PERF_ATTACH_CHILD	0x40
 
 struct perf_cgroup;
 struct perf_buffer;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 908417736f4e..639b99a318db 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2209,26 +2209,6 @@ out:
 	perf_event__header_size(leader);
 }
 
-static void sync_child_event(struct perf_event *child_event);
-
-static void perf_child_detach(struct perf_event *event)
-{
-	struct perf_event *parent_event = event->parent;
-
-	if (!(event->attach_state & PERF_ATTACH_CHILD))
-		return;
-
-	event->attach_state &= ~PERF_ATTACH_CHILD;
-
-	if (WARN_ON_ONCE(!parent_event))
-		return;
-
-	lockdep_assert_held(&parent_event->child_mutex);
-
-	sync_child_event(event);
-	list_del_init(&event->child_list);
-}
-
 static bool is_orphaned_event(struct perf_event *event)
 {
 	return event->state == PERF_EVENT_STATE_DEAD;
@@ -2336,7 +2316,6 @@ group_sched_out(struct perf_event *group_event,
 }
 
 #define DETACH_GROUP	0x01UL
-#define DETACH_CHILD	0x02UL
 
 /*
  * Cross CPU call to remove a performance event
@@ -2360,8 +2339,6 @@ __perf_remove_from_context(struct perf_event *event,
 	event_sched_out(event, cpuctx, ctx);
 	if (flags & DETACH_GROUP)
 		perf_group_detach(event);
-	if (flags & DETACH_CHILD)
-		perf_child_detach(event);
 	list_del_event(event, ctx);
 
 	if (!ctx->nr_events && ctx->is_active) {
@@ -2390,21 +2367,25 @@ static void perf_remove_from_context(struct perf_event *event, unsigned long fla
 
 	lockdep_assert_held(&ctx->mutex);
 
+	event_function_call(event, __perf_remove_from_context, (void *)flags);
+
 	/*
-	 * Because of perf_event_exit_task(), perf_remove_from_context() ought
-	 * to work in the face of TASK_TOMBSTONE, unlike every other
-	 * event_function_call() user.
+	 * The above event_function_call() can NO-OP when it hits
+	 * TASK_TOMBSTONE. In that case we must already have been detached
+	 * from the context (by perf_event_exit_event()) but the grouping
+	 * might still be in-tact.
 	 */
-	raw_spin_lock_irq(&ctx->lock);
-	if (!ctx->is_active) {
-		__perf_remove_from_context(event, __get_cpu_context(ctx),
-					   ctx, (void *)flags);
+	WARN_ON_ONCE(event->attach_state & PERF_ATTACH_CONTEXT);
+	if ((flags & DETACH_GROUP) &&
+	    (event->attach_state & PERF_ATTACH_GROUP)) {
+		/*
+		 * Since in that case we cannot possibly be scheduled, simply
+		 * detach now.
+		 */
+		raw_spin_lock_irq(&ctx->lock);
+		perf_group_detach(event);
 		raw_spin_unlock_irq(&ctx->lock);
-		return;
 	}
-	raw_spin_unlock_irq(&ctx->lock);
-
-	event_function_call(event, __perf_remove_from_context, (void *)flags);
 }
 
 /*
@@ -12296,17 +12277,14 @@ void perf_pmu_migrate_context(struct pmu *pmu, int src_cpu, int dst_cpu)
 }
 EXPORT_SYMBOL_GPL(perf_pmu_migrate_context);
 
-static void sync_child_event(struct perf_event *child_event)
+static void sync_child_event(struct perf_event *child_event,
+			       struct task_struct *child)
 {
 	struct perf_event *parent_event = child_event->parent;
 	u64 child_val;
 
-	if (child_event->attr.inherit_stat) {
-		struct task_struct *task = child_event->ctx->task;
-
-		if (task && task != TASK_TOMBSTONE)
-			perf_event_read_event(child_event, task);
-	}
+	if (child_event->attr.inherit_stat)
+		perf_event_read_event(child_event, child);
 
 	child_val = perf_event_count(child_event);
 
@@ -12321,53 +12299,60 @@ static void sync_child_event(struct perf_event *child_event)
 }
 
 static void
-perf_event_exit_event(struct perf_event *event, struct perf_event_context *ctx)
+perf_event_exit_event(struct perf_event *child_event,
+		      struct perf_event_context *child_ctx,
+		      struct task_struct *child)
 {
-	struct perf_event *parent_event = event->parent;
-	unsigned long detach_flags = 0;
-
-	if (parent_event) {
-		/*
-		 * Do not destroy the 'original' grouping; because of the
-		 * context switch optimization the original events could've
-		 * ended up in a random child task.
-		 *
-		 * If we were to destroy the original group, all group related
-		 * operations would cease to function properly after this
-		 * random child dies.
-		 *
-		 * Do destroy all inherited groups, we don't care about those
-		 * and being thorough is better.
-		 */
-		detach_flags = DETACH_GROUP | DETACH_CHILD;
-		mutex_lock(&parent_event->child_mutex);
-	}
+	struct perf_event *parent_event = child_event->parent;
 
-	perf_remove_from_context(event, detach_flags);
+	/*
+	 * Do not destroy the 'original' grouping; because of the context
+	 * switch optimization the original events could've ended up in a
+	 * random child task.
+	 *
+	 * If we were to destroy the original group, all group related
+	 * operations would cease to function properly after this random
+	 * child dies.
+	 *
+	 * Do destroy all inherited groups, we don't care about those
+	 * and being thorough is better.
+	 */
+	raw_spin_lock_irq(&child_ctx->lock);
+	WARN_ON_ONCE(child_ctx->is_active);
 
-	raw_spin_lock_irq(&ctx->lock);
-	if (event->state > PERF_EVENT_STATE_EXIT)
-		perf_event_set_state(event, PERF_EVENT_STATE_EXIT);
-	raw_spin_unlock_irq(&ctx->lock);
+	if (parent_event)
+		perf_group_detach(child_event);
+	list_del_event(child_event, child_ctx);
+	perf_event_set_state(child_event, PERF_EVENT_STATE_EXIT); /* is_event_hup() */
+	raw_spin_unlock_irq(&child_ctx->lock);
 
 	/*
-	 * Child events can be freed.
+	 * Parent events are governed by their filedesc, retain them.
 	 */
-	if (parent_event) {
-		mutex_unlock(&parent_event->child_mutex);
-		/*
-		 * Kick perf_poll() for is_event_hup();
-		 */
-		perf_event_wakeup(parent_event);
-		free_event(event);
-		put_event(parent_event);
+	if (!parent_event) {
+		perf_event_wakeup(child_event);
 		return;
 	}
+	/*
+	 * Child events can be cleaned up.
+	 */
+
+	sync_child_event(child_event, child);
 
 	/*
-	 * Parent events are governed by their filedesc, retain them.
+	 * Remove this event from the parent's list
+	 */
+	WARN_ON_ONCE(parent_event->ctx->parent_ctx);
+	mutex_lock(&parent_event->child_mutex);
+	list_del_init(&child_event->child_list);
+	mutex_unlock(&parent_event->child_mutex);
+
+	/*
+	 * Kick perf_poll() for is_event_hup().
 	 */
-	perf_event_wakeup(event);
+	perf_event_wakeup(parent_event);
+	free_event(child_event);
+	put_event(parent_event);
 }
 
 static void perf_event_exit_task_context(struct task_struct *child, int ctxn)
@@ -12424,7 +12409,7 @@ static void perf_event_exit_task_context(struct task_struct *child, int ctxn)
 	perf_event_task(child, child_ctx, 0);
 
 	list_for_each_entry_safe(child_event, next, &child_ctx->event_list, event_entry)
-		perf_event_exit_event(child_event, child_ctx);
+		perf_event_exit_event(child_event, child_ctx, child);
 
 	mutex_unlock(&child_ctx->mutex);
 
@@ -12684,7 +12669,6 @@ inherit_event(struct perf_event *parent_event,
 	 */
 	raw_spin_lock_irqsave(&child_ctx->lock, flags);
 	add_event_to_ctx(child_event, child_ctx);
-	child_event->attach_state |= PERF_ATTACH_CHILD;
 	raw_spin_unlock_irqrestore(&child_ctx->lock, flags);
 
 	/*