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=-11.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 CE369C433E6 for ; Fri, 12 Mar 2021 11:37:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A8BE964FE2 for ; Fri, 12 Mar 2021 11:37:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229748AbhCLLhH (ORCPT ); Fri, 12 Mar 2021 06:37:07 -0500 Received: from mail.kernel.org ([198.145.29.99]:47270 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231437AbhCLLgo (ORCPT ); Fri, 12 Mar 2021 06:36:44 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id ABB2C64FB9; Fri, 12 Mar 2021 11:36:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1615549004; bh=Tnmzg1VNWRp37vPZH7WBHF69zo4cruqMAptSEKsDpE4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=W/fav6v6j9c1sr6Et0T7YtmGJSMg4RyEoLnMA/co9nN/OBXrOQLJrtp+gk/6s6XAE hUK4HFynm6jq9pgRe/XG+RoYmhe0DCEyaEYPKpOWiUHyjuaaHTMt9tpES9moyFWDpj fUiQIJuEnIHdAnbTKBywNw+n1kwnJN0L3j/RuCaCstCmY2lIXWy194pwK7tD9ApdoW nYgP5ltxrab4g8LZ0bxbUwYMh0/1uPbKC9CL91Qx2ZmIaPhdWNripUKQkQ+j/DJsTZ r99jsE+iw9oPJ8NdThPjsutWFWHutaEc8x/rlYS09F6qrDSrYj3icAKZJfQU4nmjjZ Noe+S0gYjYxKw== Date: Fri, 12 Mar 2021 12:36:41 +0100 From: Frederic Weisbecker To: paulmck@kernel.org Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org Subject: Re: [PATCH tip/core/rcu 06/10] softirq: Don't try waking ksoftirqd before it has been spawned Message-ID: <20210312113641.GA3646@lothringen> References: <20210303235958.GA22373@paulmck-ThinkPad-P72> <20210304000019.22459-6-paulmck@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210304000019.22459-6-paulmck@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 03, 2021 at 04:00:15PM -0800, paulmck@kernel.org wrote: > From: "Paul E. McKenney" > > 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 CONFIG_NO_HZ_IDLE=y CONFIG_HZ_PERIODIC=n" --bootargs "threadirqs=1" --trust-make > > This commit therefore adds a couple of existence checks for ksoftirqd > and forces back-of-interrupt softirq processing when ksoftirqd does not > yet exist. With this change, the above test passes. > > Reported-by: Sebastian Andrzej Siewior > Reported-by: Uladzislau Rezki > Cc: Peter Zijlstra > Cc: Thomas Gleixner > [ paulmck: Remove unneeded check per Sebastian Siewior feedback. ] > Signed-off-by: Paul E. McKenney Reviewed-by: Frederic Weisbecker