Reapply "perf: Disallow mis-matched inherited group reads"

This reverts commit 9c20bfd64d.

It's needed back in the tree as it fixes a real issue, and it turns out
to nicely fit into an unused slot within the structure, so there's no
ABI breakage.

Update the .xml file with the new structure field:

Leaf changes summary: 1 artifact changed
Changed leaf types summary: 1 leaf type changed
Removed/Changed/Added functions summary: 0 Removed, 0 Changed, 0 Added function
Removed/Changed/Added variables summary: 0 Removed, 0 Changed, 0 Added variable

'struct perf_event at perf_event.h:564:1' changed:
  type size hasn't changed
  1 data member insertion:
    'unsigned int group_generation', at offset 1120 (in bits) at perf_event.h:601:1
  1242 impacted interfaces

Bug: 307236803
Change-Id: I921c19d115869d8b0517d44d271d56d557da4167
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

include/linux/perf_event.h

@@ -597,6 +597,9 @@ struct perf_event {
 	/* The cumulative AND of all event_caps for events in this group. */
 	int				group_caps;
 
+#ifndef __GENKSYMS__	/* ANDROID Bug: 307236803 to keep the crc preserved */
+	unsigned int			group_generation;
+#endif
 	struct perf_event		*group_leader;
 	struct pmu			*pmu;
 	void				*pmu_private;

kernel/events/core.c

@@ -1848,6 +1848,7 @@ static void perf_group_attach(struct perf_event *event)
 
 	list_add_tail(&event->sibling_list, &group_leader->sibling_list);
 	group_leader->nr_siblings++;
+	group_leader->group_generation++;
 
 	perf_event__header_size(group_leader);
 
@@ -1918,6 +1919,7 @@ static void perf_group_detach(struct perf_event *event)
 	if (event->group_leader != event) {
 		list_del_init(&event->sibling_list);
 		event->group_leader->nr_siblings--;
+		event->group_leader->group_generation++;
 		goto out;
 	}
 
@@ -4736,7 +4738,7 @@ static int __perf_read_group_add(struct perf_event *leader,
 					u64 read_format, u64 *values)
 {
 	struct perf_event_context *ctx = leader->ctx;
-	struct perf_event *sub;
+	struct perf_event *sub, *parent;
 	unsigned long flags;
 	int n = 1; /* skip @nr */
 	int ret;
@@ -4746,6 +4748,33 @@ static int __perf_read_group_add(struct perf_event *leader,
 		return ret;
 
 	raw_spin_lock_irqsave(&ctx->lock, flags);
+	/*
+	 * Verify the grouping between the parent and child (inherited)
+	 * events is still in tact.
+	 *
+	 * Specifically:
+	 *  - leader->ctx->lock pins leader->sibling_list
+	 *  - parent->child_mutex pins parent->child_list
+	 *  - parent->ctx->mutex pins parent->sibling_list
+	 *
+	 * Because parent->ctx != leader->ctx (and child_list nests inside
+	 * ctx->mutex), group destruction is not atomic between children, also
+	 * see perf_event_release_kernel(). Additionally, parent can grow the
+	 * group.
+	 *
+	 * Therefore it is possible to have parent and child groups in a
+	 * different configuration and summing over such a beast makes no sense
+	 * what so ever.
+	 *
+	 * Reject this.
+	 */
+	parent = leader->parent;
+	if (parent &&
+	    (parent->group_generation != leader->group_generation ||
+	     parent->nr_siblings != leader->nr_siblings)) {
+		ret = -ECHILD;
+		goto unlock;
+	}
 
 	/*
 	 * Since we co-schedule groups, {enabled,running} times of siblings
@@ -4775,8 +4804,9 @@ static int __perf_read_group_add(struct perf_event *leader,
 			values[n++] = primary_event_id(sub);
 	}
 
+unlock:
 	raw_spin_unlock_irqrestore(&ctx->lock, flags);
-	return 0;
+	return ret;
 }
 
 static int perf_read_group(struct perf_event *event,
@@ -4795,10 +4825,6 @@ static int perf_read_group(struct perf_event *event,
 
 	values[0] = 1 + leader->nr_siblings;
 
-	/*
-	 * By locking the child_mutex of the leader we effectively
-	 * lock the child list of all siblings.. XXX explain how.
-	 */
 	mutex_lock(&leader->child_mutex);
 
 	ret = __perf_read_group_add(leader, read_format, values);
@@ -11587,6 +11613,7 @@ static int inherit_group(struct perf_event *parent_event,
 		if (IS_ERR(child_ctr))
 			return PTR_ERR(child_ctr);
 	}
+	leader->group_generation = parent_event->group_generation;
 	return 0;
 }