linux-kernel - [tip: perf/core] perf: Simplify perf_event_release

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Message-ID: <174413910331.31282.6556072278526735885.tip-bot2@tip-bot2>
Date: Tue, 08 Apr 2025 19:05:03 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Ravi Bangoria <ravi.bangoria@....com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: perf/core] perf: Simplify perf_event_release_kernel()

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@...radead.org>
AuthorDate:    Fri, 17 Jan 2025 15:31:49 +01:00
Committer:     Peter Zijlstra <peterz@...radead.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@...radead.org>
Reviewed-by: Ravi Bangoria <ravi.bangoria@....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