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 C5C7035EF1; Fri, 23 Feb 2024 15:14:52 +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=1708701292; cv=none; b=REPWMvWb3EfBGybtOfax8LDTHsBCyVfwl5k0p/7hai8MmOif3mLdRPGq8f7qLNOygm7n/Ud/88h8pZZ+9j7FzYe/ejZrU7aX8XVH1FGaes+zMeqIcIiqrM0Wq1NU2gckw53Sqy8weE5L5b0BpYw3nWnc8M6RtAFgCP0/XAfkIz8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708701292; c=relaxed/simple; bh=7W8+QYtt2grKoqRx/oAyb0v655L0Xcbk0QRleTescoc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=evzq2ZI9pF3xAyjXRuboVI8/9C2JnDQQEaPiRTL/MKDzOzaW1zII0DTLcB6FdO7IQTy2AC20hovctZYCl5GQNQSs/zdiIiyBwoAquG+dka5sYIjQ8MGotggLx1mBz15wOEG9X0un7n4HFiB96nptctDxf3zsJtkEgXoq7sr3los= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IvLF4unx; 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="IvLF4unx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E2C7FC433C7; Fri, 23 Feb 2024 15:14:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1708701292; bh=7W8+QYtt2grKoqRx/oAyb0v655L0Xcbk0QRleTescoc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=IvLF4unxDB0rNIL0JXp0Hn4oDAPmbkGVzyPv3iUfoOeZJtZzBl7GOF6ksN0FJuxHr NrcysBwlpekCR5yYcYL61aQP2GiHY9A8lx4oA1O60976Ro7Wuhgo5otJqsQqykF1De b+bl6zWjMAxlhhUg8KdkjPEzFDop5x9AQ7x+jDq5fIilm6AaSXLMPOFocrxz3LZIz3 Y+/WU7aweJAUHkMzgMWQaeDFEZxGipIxG8mTPsT7DiqSrS97lYDAvrEZu9WrZOLQwm ue6ioQIgjLQ5oJTvKGV2a7RE1apuaaNMkbCetf4FLMrc0zEOFDfFu2DtCr6JpKmsJI eNQ9x1LvGbKKQ== Date: Fri, 23 Feb 2024 16:14:49 +0100 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: Boqun Feng , linux-kernel@vger.kernel.org, rcu@vger.kernel.org, Neeraj Upadhyay , Thomas Gleixner , Sebastian Siewior , Anna-Maria Behnsen , Steven Rostedt , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Mathieu Desnoyers , Lai Jiangshan , Zqiang Subject: Re: [PATCH v2 6/6] rcu-tasks: Maintain real-time response in rcu_tasks_postscan() Message-ID: References: <20240217012745.3446231-1-boqun.feng@gmail.com> <20240217012745.3446231-7-boqun.feng@gmail.com> <9a27f638-4eb0-42b3-b8a3-201d6ed9406b@paulmck-laptop> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Feb 23, 2024 at 01:17:14PM +0100, Frederic Weisbecker wrote: > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h > index 866743e0796f..0ff2b554f5b5 100644 > --- a/kernel/rcu/tasks.h > +++ b/kernel/rcu/tasks.h > @@ -973,12 +973,13 @@ static void rcu_tasks_postscan(struct list_head *hop) > for_each_possible_cpu(cpu) { > unsigned long j = jiffies + 1; > struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rcu_tasks.rtpcpu, cpu); > - struct task_struct *t; > - struct task_struct *t1; > - struct list_head tmp; > > raw_spin_lock_irq_rcu_node(rtpcp); > - list_for_each_entry_safe(t, t1, &rtpcp->rtp_exit_list, rcu_tasks_exit_list) { > + while (!list_empty(&rtpcp->rtp_exit_list)) { > + struct task_struct *t; > + t = list_first_entry(&rtpcp->rtp_exit_list, typeof(*t), rcu_tasks_exit_list); > + list_del_init(&t->rcu_tasks_exit_list); Oh no! The task has to stay in the list for subsequent grace periods! Please forget that suggestion... Yours looks good! Thanks. > + > if (list_empty(&t->rcu_tasks_holdout_list)) > rcu_tasks_pertask(t, hop); > > @@ -987,14 +988,9 @@ static void rcu_tasks_postscan(struct list_head *hop) > if (!IS_ENABLED(CONFIG_PREEMPT_RT) && time_before(jiffies, j)) > continue; > > - // Keep our place in the list while pausing. > - // Nothing else traverses this list, so adding a > - // bare list_head is OK. > - list_add(&tmp, &t->rcu_tasks_exit_list); > raw_spin_unlock_irq_rcu_node(rtpcp); > cond_resched(); // For CONFIG_PREEMPT=n kernels > raw_spin_lock_irq_rcu_node(rtpcp); > - list_del(&tmp); > j = jiffies + 1; > } > raw_spin_unlock_irq_rcu_node(rtpcp); > @@ -1219,7 +1215,6 @@ void exit_tasks_rcu_stop(void) > struct rcu_tasks_percpu *rtpcp; > struct task_struct *t = current; > > - 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); >