There is no good reason to have the free list anymore. It is possible
to call free_event() after the locks have been dropped in the main
loop.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/events/core.c |   12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5462,7 +5462,6 @@ int perf_event_release_kernel(struct per
 {
 	struct perf_event_context *ctx = event->ctx;
 	struct perf_event *child, *tmp;
-	LIST_HEAD(free_list);
 
 	/*
 	 * If we got here through err_alloc: free_event(event); we will not
@@ -5531,27 +5530,26 @@ int perf_event_release_kernel(struct per
 					       struct perf_event, child_list);
 		if (tmp == child) {
 			perf_remove_from_context(child, DETACH_GROUP | DETACH_CHILD);
-			list_add(&child->child_list, &free_list);
 			/*
 			 * This matches the refcount bump in inherit_event();
 			 * this can't be the last reference.
 			 */
 			put_event(event);
+		} else {
+			child = NULL;
 		}
 
 		mutex_unlock(&event->child_mutex);
 		mutex_unlock(&ctx->mutex);
+
+		if (child)
+			free_event(child);
 		put_ctx(ctx);
 
 		goto again;
 	}
 	mutex_unlock(&event->child_mutex);
 
-	list_for_each_entry_safe(child, tmp, &free_list, child_list) {
-		list_del(&child->child_list);
-		free_event(child);
-	}
-
 no_ctx:
 	put_event(event); /* Must be the 'last' reference */
 	return 0;

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     3e8671e00e57b3d006ed8ae5ef055807506e44b2
Gitweb:        https://git.kernel.org/tip/3e8671e00e57b3d006ed8ae5ef055807506e44b2
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Fri, 17 Jan 2025 15:31:49 +01:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 08 Apr 2025 20:55:47 +02:00

perf: Simplify perf_event_release_kernel()

There is no good reason to have the free list anymore. It is possible
to call free_event() after the locks have been dropped in the main
loop.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ravi Bangoria <ravi.bangoria@amd.com>
Link: https://lkml.kernel.org/r/20250307193723.151721102@infradead.org
---
 kernel/events/core.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index fa6dab0..f75b0d3 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5696,7 +5696,6 @@ int perf_event_release_kernel(struct perf_event *event)
 {
 	struct perf_event_context *ctx = event->ctx;
 	struct perf_event *child, *tmp;
-	LIST_HEAD(free_list);
 
 	/*
 	 * If we got here through err_alloc: free_event(event); we will not
@@ -5765,23 +5764,23 @@ again:
 					       struct perf_event, child_list);
 		if (tmp == child) {
 			perf_remove_from_context(child, DETACH_GROUP | DETACH_CHILD);
-			list_add(&child->child_list, &free_list);
+		} else {
+			child = NULL;
 		}
 
 		mutex_unlock(&event->child_mutex);
 		mutex_unlock(&ctx->mutex);
+
+		if (child) {
+			/* Last reference unless ->pending_task work is pending */
+			put_event(child);
+		}
 		put_ctx(ctx);
 
 		goto again;
 	}
 	mutex_unlock(&event->child_mutex);
 
-	list_for_each_entry_safe(child, tmp, &free_list, child_list) {
-		list_del(&child->child_list);
-		/* Last reference unless ->pending_task work is pending */
-		put_event(child);
-	}
-
 no_ctx:
 	/*
 	 * Last reference unless ->pending_task work is pending on this event