Commit 94be133f authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'perf-urgent-2023-10-21' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull perf events fix from Ingo Molnar:
 "Fix group event semantics"

* tag 'perf-urgent-2023-10-21' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  perf: Disallow mis-matched inherited group reads
parents 023cc836 32671e37

include/linux/perf_event.h

+1 −0
Original line number Diff line number Diff line
@@ -704,6 +704,7 @@ struct perf_event { 
	/* The cumulative AND of all event_caps for events in this group. */

	int				group_caps;



	unsigned int			group_generation;

	struct perf_event		*group_leader;

	/*

	 * event->pmu will always point to pmu in which this event belongs.

kernel/events/core.c

+33 −6
Original line number Diff line number Diff line
@@ -1954,6 +1954,7 @@ 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);
@@ -2144,6 +2145,7 @@ static void perf_group_detach(struct perf_event *event) 
	if (leader != event) {

		list_del_init(&event->sibling_list);

		event->group_leader->nr_siblings--;

		event->group_leader->group_generation++;

		goto out;

	}
@@ -5440,7 +5442,7 @@ 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;
@@ -5450,6 +5452,33 @@ 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
@@ -5483,8 +5512,9 @@ static int __perf_read_group_add(struct perf_event *leader, 
			values[n++] = atomic64_read(&sub->lost_samples);

	}



unlock:

	raw_spin_unlock_irqrestore(&ctx->lock, flags);

	return 0;

	return ret;

}



static int perf_read_group(struct perf_event *event,
@@ -5503,10 +5533,6 @@ 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);
@@ -13346,6 +13372,7 @@ static int inherit_group(struct perf_event *parent_event, 
		    !perf_get_aux_event(child_ctr, leader))

			return -EINVAL;

	}

	leader->group_generation = parent_event->group_generation;

	return 0;

}