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 AACF725A2C0; Tue, 25 Mar 2025 12:27:05 +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=1742905625; cv=none; b=Vj500FNawtrbcEY7d2QOXz0DVXaFWbjSFL0P1v8LyGXF7fIgVvwMy4dmoGt1DaaRZXTlkbZQAvmoQuWgV2eyNCGFs+rGekNS1NbRisgJAQRFoz5aNjMbkezvnAABK4iETAEIQgm/riFQ6kbMhkg8yfScvbB50kvFL5v6cVQjbMU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742905625; c=relaxed/simple; bh=UXSdBcKyN88grZrvEi7fevU+Fjgkp4WVo8wTcf6c9pw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Jq/Evk4mgWf+MaaXAwQEXj4IXf4eliJObWEZXYOyDRL68Y9MwamiQYrdToFjc2f4IvNVQFANb9arLRxaQ2J1f7UMWeekgakCW7YQMI6YRvPdla2rJAgmV0Rscs8jARtMCpzLEVx2epQcM+IquS86dndW50ktfD2Xi09lcudJ7dA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=kqrwS3ku; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="kqrwS3ku" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E1988C4CEE9; Tue, 25 Mar 2025 12:27:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1742905625; bh=UXSdBcKyN88grZrvEi7fevU+Fjgkp4WVo8wTcf6c9pw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kqrwS3kuFiBHR7ekl+wN1kpeyZ5fWnyl2Z4S7eVFGdkStXLlmefdatNMLAltGvDEY oGm9966IdBTysRzCr/gyzTk/EKM88UN1oKp7SiZF1H99bGeVqdKcAeivs5HkjeegOS eCHrKfTpo1MvtrcjiQFgFQBOpeZUIfrOYAvIVoWs= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jann Horn , "Peter Zijlstra (Intel)" , Sasha Levin Subject: [PATCH 6.1 046/198] sched: Clarify wake_up_q()s write to task->wake_q.next Date: Tue, 25 Mar 2025 08:20:08 -0400 Message-ID: <20250325122157.843620662@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250325122156.633329074@linuxfoundation.org> References: <20250325122156.633329074@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ 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 9be8a509b5f3f..9b01fdceb6220 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -997,9 +997,10 @@ 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