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 E0B7B393DCF; Wed, 17 Sep 2025 12:55:01 +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=1758113702; cv=none; b=rW11cds5p1XaZLV2ZrZNYwObMTF2Yc9suNS7JKcFKJxdKl5r8pMn101YGBvxHuqh7v1L4YoNL/RhzEY3+Suvuls3PhVWeXokw7qF4j+58INrwCiu3oX+speemQwAqAYB4FuUCEztHJRyc0RVpV18EWrsM07SsQNtnKX9S0K/8a0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758113702; c=relaxed/simple; bh=uULbrCLYaeZ0WX6ar1719C0fJAAQyY/193keGBzx+aQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Xr7+X4zfYsHq6ti4vSti29VWSzvVSYQUTWjCrv7uGvtM3VeNOuCAZzRnLdV/EZQ4M0gs31P/vQ7XALXHTDNKfbzrLo3LqIFZp+bKXnreHdoOofiXtO4TRWqG2tTo6LsEprXijyvGFwnrqfGe/ExfRrJDqKrdafCfCB2o6rnyHk4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Qqn2ftc7; 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="Qqn2ftc7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6266DC4CEF0; Wed, 17 Sep 2025 12:55:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1758113701; bh=uULbrCLYaeZ0WX6ar1719C0fJAAQyY/193keGBzx+aQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Qqn2ftc7twBiNvU7ZAF7aKeIARmG26tHkRJAEIrqFEsPSuI91ctj4z9t3YMIkDQJn fIsQG0LQ8r80sfMfJ51dvKBikMhXikSnTGFuys7e6zDqorWmOvzSoitGSirR3ivT+P vEWC4+5RrKhR2hxXCnrPwyot0+cabX5+fK1IcBS0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Chen Zhongjin , Yang Jihong , "Paul E. McKenney" , Frederic Weisbecker , Boqun Feng , Tahera Fahimi Subject: [PATCH 6.6 027/101] rcu-tasks: Maintain lists to eliminate RCU-tasks/do_exit() deadlocks Date: Wed, 17 Sep 2025 14:34:10 +0200 Message-ID: <20250917123337.512507812@linuxfoundation.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20250917123336.863698492@linuxfoundation.org> References: <20250917123336.863698492@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Paul E. McKenney commit 6b70399f9ef3809f6e308fd99dd78b072c1bd05c upstream. This commit continues the elimination of deadlocks involving do_exit() and RCU tasks by causing exit_tasks_rcu_start() to add the current task to a per-CPU list and causing exit_tasks_rcu_stop() to remove the current task from whatever list it is on. These lists will be used to track tasks that are exiting, while still accounting for any RCU-tasks quiescent states that these tasks pass though. [ paulmck: Apply Frederic Weisbecker feedback. ] Link: https://lore.kernel.org/all/20240118021842.290665-1-chenzhongjin@huawei.com/ Reported-by: Chen Zhongjin Reported-by: Yang Jihong Signed-off-by: Paul E. McKenney Tested-by: Yang Jihong Tested-by: Chen Zhongjin Reviewed-by: Frederic Weisbecker Signed-off-by: Boqun Feng Cc: Tahera Fahimi Signed-off-by: Greg Kroah-Hartman --- kernel/rcu/tasks.h | 43 +++++++++++++++++++++++++++++++++---------- 1 file changed, 33 insertions(+), 10 deletions(-) --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -1175,25 +1175,48 @@ struct task_struct *get_rcu_tasks_gp_kth EXPORT_SYMBOL_GPL(get_rcu_tasks_gp_kthread); /* - * Contribute to protect against tasklist scan blind spot while the - * task is exiting and may be removed from the tasklist. See - * corresponding synchronize_srcu() for further details. + * Protect against tasklist scan blind spot while the task is exiting and + * may be removed from the tasklist. Do this by adding the task to yet + * another list. + * + * Note that the task will remove itself from this list, so there is no + * need for get_task_struct(), except in the case where rcu_tasks_pertask() + * adds it to the holdout list, in which case rcu_tasks_pertask() supplies + * the needed get_task_struct(). */ -void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu) +void exit_tasks_rcu_start(void) { - current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu); + unsigned long flags; + struct rcu_tasks_percpu *rtpcp; + struct task_struct *t = current; + + WARN_ON_ONCE(!list_empty(&t->rcu_tasks_exit_list)); + preempt_disable(); + rtpcp = this_cpu_ptr(rcu_tasks.rtpcpu); + t->rcu_tasks_exit_cpu = smp_processor_id(); + raw_spin_lock_irqsave_rcu_node(rtpcp, flags); + if (!rtpcp->rtp_exit_list.next) + INIT_LIST_HEAD(&rtpcp->rtp_exit_list); + list_add(&t->rcu_tasks_exit_list, &rtpcp->rtp_exit_list); + raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); + preempt_enable(); } /* - * Contribute to protect against tasklist scan blind spot while the - * task is exiting and may be removed from the tasklist. See - * corresponding synchronize_srcu() for further details. + * Remove the task from the "yet another list" because do_exit() is now + * non-preemptible, allowing synchronize_rcu() to wait beyond this point. */ -void exit_tasks_rcu_stop(void) __releases(&tasks_rcu_exit_srcu) +void exit_tasks_rcu_stop(void) { + unsigned long flags; + struct rcu_tasks_percpu *rtpcp; struct task_struct *t = current; - __srcu_read_unlock(&tasks_rcu_exit_srcu, t->rcu_tasks_idx); + WARN_ON_ONCE(list_empty(&t->rcu_tasks_exit_list)); + rtpcp = per_cpu_ptr(rcu_tasks.rtpcpu, t->rcu_tasks_exit_cpu); + raw_spin_lock_irqsave_rcu_node(rtpcp, flags); + list_del_init(&t->rcu_tasks_exit_list); + raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); } /*