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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 D943FC4167B for ; Mon, 7 Dec 2020 11:48:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A4F5F23340 for ; Mon, 7 Dec 2020 11:48:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726874AbgLGLs2 (ORCPT ); Mon, 7 Dec 2020 06:48:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43132 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726370AbgLGLs2 (ORCPT ); Mon, 7 Dec 2020 06:48:28 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 45156C0613D0 for ; Mon, 7 Dec 2020 03:47:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=edP2H5YMzTq6JDL5+Mwz3TSesMidmvdEM37da6u28Ng=; b=xJRNEc1nQVU5maBnwk6Y0WRQNL tMlybxaeMVkp6INeWlcl+KqGuMQgbAQA4I6a8FQjkzEi07ShBuiIWUHb3CkwFi6QqGliblhKZyoTt 4cc5KJaZiYykRsYVeu/61mPE5HNDG23kGWfoEb1Q4HXWUV1r/6HGJCCBJYpT/kjpWpN7No1a5GYbA /Xc4BZVqOTUeIEz9Z4RUFQsEylCsamgxo0PMRswxhPVO5nCjFOuJzODqciDQzJ33oGvjM2aERhaRq ljRQ+f1GyR8rXvW95nCU42hvDwaqKAlOVnF18j2ImrxTdLudgHKl3MMY6mDjHAV9Eu+UnV/J/mRRx a0XUj1Zg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kmEzZ-0003LX-6a; Mon, 07 Dec 2020 11:47:45 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id D0CEB301478; Mon, 7 Dec 2020 12:47:43 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BBE3E2081295B; Mon, 7 Dec 2020 12:47:43 +0100 (CET) Date: Mon, 7 Dec 2020 12:47:43 +0100 From: Peter Zijlstra To: Thomas Gleixner Cc: LKML , Frederic Weisbecker , Paul McKenney , Sebastian Andrzej Siewior Subject: Re: [patch V2 9/9] tasklets: Prevent kill/unlock_wait deadlock on RT Message-ID: <20201207114743.GK3040@hirez.programming.kicks-ass.net> References: <20201204170151.960336698@linutronix.de> <20201204170805.627618080@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201204170805.627618080@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 04, 2020 at 06:02:00PM +0100, Thomas Gleixner wrote: > @@ -825,7 +848,20 @@ void tasklet_kill(struct tasklet_struct > > while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) { > do { > - yield(); > } while (test_bit(TASKLET_STATE_SCHED, &t->state)); > } > tasklet_unlock_wait(t); Egads... should we not start by doing something like this? --- diff --git a/kernel/softirq.c b/kernel/softirq.c index d5bfd5e661fc..95ff5b7f1833 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -529,6 +529,16 @@ void __tasklet_hi_schedule(struct tasklet_struct *t) } EXPORT_SYMBOL(__tasklet_hi_schedule); +static inline bool tasklet_clear_sched(struct tasklet_struct *t) +{ + if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) { + wake_up_var(&t->state); + return true; + } + + return false; +} + static void tasklet_action_common(struct softirq_action *a, struct tasklet_head *tl_head, unsigned int softirq_nr) @@ -548,8 +558,7 @@ static void tasklet_action_common(struct softirq_action *a, if (tasklet_trylock(t)) { if (!atomic_read(&t->count)) { - if (!test_and_clear_bit(TASKLET_STATE_SCHED, - &t->state)) + if (!tasklet_clear_sched(t)) BUG(); if (t->use_callback) t->callback(t); @@ -609,13 +618,11 @@ void tasklet_kill(struct tasklet_struct *t) if (in_interrupt()) pr_notice("Attempt to kill tasklet from interrupt\n"); - while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) { - do { - yield(); - } while (test_bit(TASKLET_STATE_SCHED, &t->state)); - } + while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) + wait_var_event(&t->state, !test_bit(TASKLET_STATE_SCHED, &t->state)); + tasklet_unlock_wait(t); - clear_bit(TASKLET_STATE_SCHED, &t->state); + tasklet_clear_sched(t); } EXPORT_SYMBOL(tasklet_kill);