From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3B04FC433DB for ; Sat, 13 Feb 2021 16:46:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 04F7761494 for ; Sat, 13 Feb 2021 16:46:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229775AbhBMQqi (ORCPT ); Sat, 13 Feb 2021 11:46:38 -0500 Received: from mail.kernel.org ([198.145.29.99]:60794 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229625AbhBMQqf (ORCPT ); Sat, 13 Feb 2021 11:46:35 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 9B7F564DA5; Sat, 13 Feb 2021 16:45:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1613234754; bh=jGSbr1M3Yj/nuhpGBLy8cDOzqEIi1xrb82/vxO//Qhs=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=APVab3ydXvZS2HmmOlqOcq63EtV9mW9RdtEZSLkCDQGaZToxihx3TN+jA0tjdA0zD bs+MpcjcAjVEjbsIs6W+ZHBx9G/bz27a9W594yEXK1P/HVhi0jI9UtIv6GHMZMYHSJ l94ghzXOAHfzx4/j7XkzKHIy4ESeWw9Dr/xalYTqS0/RyDDtY1PhpdrEyrbW9BdScg H6ESf3JVyZRF02spJCTo4txXU8OehnWTeUeU/6wvDrUiN5StBYyjgW+oYmUSSOLKBL 865r79ZUosYIV/j3n/Fe1pvnEMY+2bilcQizRuCDfhp1FrybFyvZiww3l4X3IpXrQe LFH1AFcIHB/+Q== Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 6B0C73522F70; Sat, 13 Feb 2021 08:45:54 -0800 (PST) Date: Sat, 13 Feb 2021 08:45:54 -0800 From: "Paul E. McKenney" To: Uladzislau Rezki Cc: Sebastian Andrzej Siewior , LKML , RCU , Michael Ellerman , Andrew Morton , Daniel Axtens , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Peter Zijlstra , Michal Hocko , Thomas Gleixner , "Theodore Y . Ts'o" , Oleksiy Avramchenko Subject: Re: [PATCH 2/2] rcu-tasks: add RCU-tasks self tests Message-ID: <20210213164554.GS2743@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20201209202732.5896-1-urezki@gmail.com> <20201209202732.5896-2-urezki@gmail.com> <20210212192059.wytqwdf4qm4rnq3d@linutronix.de> <20210212211207.GA2046@pc638.lan> <20210212234851.GP2743@paulmck-ThinkPad-P72> <20210213003709.GA27846@paulmck-ThinkPad-P72> <20210213004328.GB27846@paulmck-ThinkPad-P72> <20210213113030.GA1878@pc638.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210213113030.GA1878@pc638.lan> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Feb 13, 2021 at 12:30:30PM +0100, Uladzislau Rezki wrote: > On Fri, Feb 12, 2021 at 04:43:28PM -0800, Paul E. McKenney wrote: > > On Fri, Feb 12, 2021 at 04:37:09PM -0800, Paul E. McKenney wrote: > > > On Fri, Feb 12, 2021 at 03:48:51PM -0800, Paul E. McKenney wrote: > > > > On Fri, Feb 12, 2021 at 10:12:07PM +0100, Uladzislau Rezki wrote: > > > > > On Fri, Feb 12, 2021 at 08:20:59PM +0100, Sebastian Andrzej Siewior wrote: > > > > > > On 2020-12-09 21:27:32 [+0100], Uladzislau Rezki (Sony) wrote: > > > > > > > Add self tests for checking of RCU-tasks API functionality. > > > > > > > It covers: > > > > > > > - wait API functions; > > > > > > > - invoking/completion call_rcu_tasks*(). > > > > > > > > > > > > > > Self-tests are run when CONFIG_PROVE_RCU kernel parameter is set. > > > > > > > > > > > > I just bisected to this commit. By booting with `threadirqs' I end up > > > > > > with: > > > > > > [ 0.176533] Running RCU-tasks wait API self tests > > > > > > > > > > > > No stall warning or so. > > > > > > It boots again with: > > > > > > > > > > > > diff --git a/init/main.c b/init/main.c > > > > > > --- a/init/main.c > > > > > > +++ b/init/main.c > > > > > > @@ -1489,6 +1489,7 @@ void __init console_on_rootfs(void) > > > > > > fput(file); > > > > > > } > > > > > > > > > > > > +void rcu_tasks_initiate_self_tests(void); > > > > > > static noinline void __init kernel_init_freeable(void) > > > > > > { > > > > > > /* > > > > > > @@ -1514,6 +1515,7 @@ static noinline void __init kernel_init_freeable(void) > > > > > > > > > > > > rcu_init_tasks_generic(); > > > > > > do_pre_smp_initcalls(); > > > > > > + rcu_tasks_initiate_self_tests(); > > > > > > lockup_detector_init(); > > > > > > > > > > > > smp_init(); > > > > > > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h > > > > > > --- a/kernel/rcu/tasks.h > > > > > > +++ b/kernel/rcu/tasks.h > > > > > > @@ -1266,7 +1266,7 @@ static void test_rcu_tasks_callback(struct rcu_head *rhp) > > > > > > rttd->notrun = true; > > > > > > } > > > > > > > > > > > > -static void rcu_tasks_initiate_self_tests(void) > > > > > > +void rcu_tasks_initiate_self_tests(void) > > > > > > { > > > > > > pr_info("Running RCU-tasks wait API self tests\n"); > > > > > > #ifdef CONFIG_TASKS_RCU > > > > > > @@ -1322,7 +1322,6 @@ void __init rcu_init_tasks_generic(void) > > > > > > #endif > > > > > > > > > > > > // Run the self-tests. > > > > > > - rcu_tasks_initiate_self_tests(); > > > > > > } > > > > > > > > > > > > #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ > > > > > > > > > > > > > Signed-off-by: Uladzislau Rezki (Sony) > > > > > > > > Apologies for the hassle! My testing clearly missed this combination > > > > of CONFIG_PROVE_RCU=y and threadirqs=1. :-( > > > > > > > > But at least I can easily reproduce this hang as follows: > > > > > > > > tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 2 --configs "TREE03" --kconfig "CONFIG_DEBUG_LOCK_ALLOC=y CONFIG_PROVE_LOCKING=y" --bootargs "threadirqs=1" --trust-make > > > > > > > > Sadly, I cannot take your patch because that simply papers over the > > > > fact that early boot use of synchronize_rcu_tasks() is broken in this > > > > particular configuration, which will likely eventually bite others now > > > > that init_kprobes() has been moved earlier in boot: > > > > > > > > 1b04fa990026 ("rcu-tasks: Move RCU-tasks initialization to before early_initcall()") > > > > Link: https://lore.kernel.org/rcu/87eekfh80a.fsf@dja-thinkpad.axtens.net/ > > > > Fixes: 36dadef23fcc ("kprobes: Init kprobes in early_initcall") > > > > > > > > > > Sebastian > > > > > > > > > > > We should be able to use call_rcu_tasks() in the *initcall() callbacks. > > > > > The problem is that, ksoftirqd threads are not spawned by the time when > > > > > an rcu_init_tasks_generic() is invoked: > > > > > > > > > > diff --git a/init/main.c b/init/main.c > > > > > index c68d784376ca..e6106bb12b2d 100644 > > > > > --- a/init/main.c > > > > > +++ b/init/main.c > > > > > @@ -954,7 +954,6 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void) > > > > > rcu_init_nohz(); > > > > > init_timers(); > > > > > hrtimers_init(); > > > > > - softirq_init(); > > > > > timekeeping_init(); > > > > > > > > > > /* > > > > > @@ -1512,6 +1511,7 @@ static noinline void __init kernel_init_freeable(void) > > > > > > > > > > init_mm_internals(); > > > > > > > > > > + softirq_init(); > > > > > rcu_init_tasks_generic(); > > > > > do_pre_smp_initcalls(); > > > > > lockup_detector_init(); > > > > > diff --git a/kernel/softirq.c b/kernel/softirq.c > > > > > index 9d71046ea247..cafa55c496d0 100644 > > > > > --- a/kernel/softirq.c > > > > > +++ b/kernel/softirq.c > > > > > @@ -630,6 +630,7 @@ void __init softirq_init(void) > > > > > &per_cpu(tasklet_hi_vec, cpu).head; > > > > > } > > > > > > > > > > + spawn_ksoftirqd(); > > > > > > > > We need a forward reference to allow this to build, but with that added, > > > > my test case passes. Good show! > > > > > > > > > open_softirq(TASKLET_SOFTIRQ, tasklet_action); > > > > > open_softirq(HI_SOFTIRQ, tasklet_hi_action); > > > > > } > > > > > @@ -732,7 +733,6 @@ static __init int spawn_ksoftirqd(void) > > > > > > > > > > return 0; > > > > > } > > > > > -early_initcall(spawn_ksoftirqd); > > > > > > > > > > /* > > > > > * [ These __weak aliases are kept in a separate compilation unit, so that > > > > > > > > > > Any thoughts? > > > > > > > > One likely problem is that there are almost certainly parts of the kernel > > > > that need softirq_init() to stay roughly where it is. So, is it possible > > > > to leave softirq_init() where it is, and to arrange for spawn_ksoftirqd() > > > > to be invoked just before rcu_init_tasks_generic() is called? > > > > > > This still seems worth trying (and doing so is next on my list), but just > > > > And the patch below takes this approach, which also causes the tests to > > pass. > > > > Thoughts? > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > commit f4cd768e341486655c8c196e1f2b48a4463541f3 > > Author: Paul E. McKenney > > Date: Fri Feb 12 16:41:05 2021 -0800 > > > > softirq: Don't try waking ksoftirqd before it has been spawned > > > > If there is heavy softirq activity, the softirq system will attempt > > to awaken ksoftirqd and will stop the traditional back-of-interrupt > > softirq processing. This is all well and good, but only if the > > ksoftirqd kthreads already exist, which is not the case during early > > boot, in which case the system hangs. > > > > One reproducer is as follows: > > > > tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 2 --configs "TREE03" --kconfig "CONFIG_DEBUG_LOCK_ALLOC=y CONFIG_PROVE_LOCKING=y" --bootargs "threadirqs=1" --trust-make > > > > This commit therefore moves the spawning of the ksoftirqd kthreads > > earlier in boot. With this change, the above test passes. > > > > Reported-by: Sebastian Andrzej Siewior > > Reported-by: Uladzislau Rezki > > Inspired-by: Uladzislau Rezki > > Signed-off-by: Paul E. McKenney > > > > diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h > > index bb8ff90..283a02d 100644 > > --- a/include/linux/interrupt.h > > +++ b/include/linux/interrupt.h > > @@ -592,6 +592,8 @@ static inline struct task_struct *this_cpu_ksoftirqd(void) > > return this_cpu_read(ksoftirqd); > > } > > > > +int spawn_ksoftirqd(void); > > + > > /* Tasklets --- multithreaded analogue of BHs. > > > > This API is deprecated. Please consider using threaded IRQs instead: > > diff --git a/init/main.c b/init/main.c > > index c68d784..99835bb 100644 > > --- a/init/main.c > > +++ b/init/main.c > > @@ -1512,6 +1512,7 @@ static noinline void __init kernel_init_freeable(void) > > > > init_mm_internals(); > > > > + spawn_ksoftirqd(); > > rcu_init_tasks_generic(); > > do_pre_smp_initcalls(); > > lockup_detector_init(); > > diff --git a/kernel/softirq.c b/kernel/softirq.c > > index 9d71046..45d50d4 100644 > > --- a/kernel/softirq.c > > +++ b/kernel/softirq.c > > @@ -724,7 +724,7 @@ static struct smp_hotplug_thread softirq_threads = { > > .thread_comm = "ksoftirqd/%u", > > }; > > > > -static __init int spawn_ksoftirqd(void) > > +__init int spawn_ksoftirqd(void) > > { > > cpuhp_setup_state_nocalls(CPUHP_SOFTIRQ_DEAD, "softirq:dead", NULL, > > takeover_tasklets); > > @@ -732,7 +732,6 @@ static __init int spawn_ksoftirqd(void) > > > > return 0; > > } > > -early_initcall(spawn_ksoftirqd); > > > > /* > > * [ These __weak aliases are kept in a separate compilation unit, so that > > > I thought about this approach as a first step how to fix it, but then came up with > moving the spawn_ksoftirqd(void); into the softirq_init() to make it consolidated > at one place and not spread. > > Then moving the softirq_init() down may cause other drawbacks, like you mentioned > if somebody needs it earlier. > > I agree with your approach. Invoking the spawn_ksoftirqd() before the rcu_init_tasks_generic() > makes it safe. At least it prevents other parts to be broken comparing with touching > and moving softirq_init(). Glad you like it! But let's see which (if any) of these patches solves the problem for Sebastian. Thanx, Paul