From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0BFAE27FE80; Tue, 18 Feb 2025 20:28:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739910536; cv=none; b=RnQurTEBrnZDsCkFI5u8jabhAqhFxYhn3pmCB1yLaAWNFUlT1lxaSuauy+OMDlYfZ8lFWPM1yu+d8VyXTQskvhKfnFxVuooOgrQzSH8iL0aDMENoUZ/gtX1Tab6U/YFEgo/HVormeekEJCOeycUqYIJix8GF7nkiIh1OvrI5ULc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739910536; c=relaxed/simple; bh=a87rZdPEARenF3+fqrfFtBkmAqq/vfWtNdwo4OzzrAc=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=FAIrhJ5NtHA6h7hmFuPgc7iAmRZMbPl+P637vnSa49T2NiKxSkohAd4rwbBVn+QN2MZK45a1qQ8JGzoVJ+admgyjP2VAOUD24LiD2oof3E4gjvVDDpxF7CO1GmFH/t9aZ6wAPPcKBzjK3Mcbsll8/qUVuUc61xbY4SUB19+gWPY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YqEEFCD5; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="YqEEFCD5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 090C8C4CEE4; Tue, 18 Feb 2025 20:28:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1739910535; bh=a87rZdPEARenF3+fqrfFtBkmAqq/vfWtNdwo4OzzrAc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YqEEFCD56OKIZ+kKbimQG/TcHO47Tv/48eg5yYMHgMh1IeBUr9l5jd8XTs3miKMSA ioYS3Y5zsDTaIA2CnRvuvRJJp1j4JpgPC8ZNpu2En2BhZImo/O0CFQ4/7rBkXylZ/J dj4qf9jkMWo1YSj9vQz7Ay0XBszvQZz2z6lbMNULcJRmreVFTx9S4dNRlY0uqupRNT kpUCfQ9HFi63AGUtRzlho8k+qs+9cWoFa8Z9HwT3PtmlptkVuG6ijtkO/NpbqMvOcu PSzafrkBpa/UPE9gmhQkxdpqHQ5t4VAqjY0MOfqURz5vliXKo+LitLSj5uMsBqdTCh iuttpS/ClyxzQ== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Jann Horn , Peter Zijlstra , Sasha Levin , mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org Subject: [PATCH AUTOSEL 5.15 3/6] sched: Clarify wake_up_q()'s write to task->wake_q.next Date: Tue, 18 Feb 2025 15:28:44 -0500 Message-Id: <20250218202848.3593863-3-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250218202848.3593863-1-sashal@kernel.org> References: <20250218202848.3593863-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 5.15.178 Content-Transfer-Encoding: 8bit From: Jann Horn [ Upstream commit bcc6244e13b4d4903511a1ea84368abf925031c0 ] Clarify that wake_up_q() does an atomic write to task->wake_q.next, after which a concurrent __wake_q_add() can immediately overwrite task->wake_q.next again. Signed-off-by: Jann Horn Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20250129-sched-wakeup-prettier-v1-1-2f51f5f663fa@google.com Signed-off-by: Sasha Levin --- kernel/sched/core.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index ed92b75f7e024..fcdf8aaaa37cb 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -939,9 +939,10 @@ void wake_up_q(struct wake_q_head *head) struct task_struct *task; task = container_of(node, struct task_struct, wake_q); - /* Task can safely be re-inserted now: */ node = node->next; - task->wake_q.next = NULL; + /* pairs with cmpxchg_relaxed() in __wake_q_add() */ + WRITE_ONCE(task->wake_q.next, NULL); + /* Task can safely be re-inserted now. */ /* * wake_up_process() executes a full barrier, which pairs with -- 2.39.5