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=-6.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 2F738C388F7 for ; Fri, 13 Nov 2020 14:24:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F15EB22226 for ; Fri, 13 Nov 2020 14:24:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="CaNkSgmH"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="0cKyj2lL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726611AbgKMOYt (ORCPT ); Fri, 13 Nov 2020 09:24:49 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:52960 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726930AbgKMOYk (ORCPT ); Fri, 13 Nov 2020 09:24:40 -0500 Message-Id: <20201113141734.907075915@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1605277477; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: references:references; bh=YBANw5+gKo0StNgfq2DAY2w568FUqe7IjvTxRxyhO0o=; b=CaNkSgmHOT8cChidgcipppyqnkXkMwbX36+aFt96F4A75TGeSz5Zhl+di5OltLmYsPtOcx quLDc5LLj6LblcQBRv5T8U2YTKstywSV4Fnr3VcKozPIF6fRJYoUQ1Olop/0XEo/nvWuKK AaWYWZNs1SHuSgrkR+sSNNUqkK/BZ+Mzqxcz+uw6LWxyeMfi7P4VPTLfGShWD5dSRZcvmV k6G5XKLQZrLBaSh78ZCTGlgHOMm+unqZIPu2euxm/TvxLdSaJIG/Ema0BvWrq4w4cjd3wq /o6/AEK8K3F6hkA6SrcnJ6gUpmrTkYW/8FpCsAN598OKXx8HQHBM1zasSFWkjA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1605277477; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: references:references; bh=YBANw5+gKo0StNgfq2DAY2w568FUqe7IjvTxRxyhO0o=; b=0cKyj2lLbsO8b/2NxbYx+cHBAmiqLRZavh3aPgFuRABbFMMdYZx0eS73Lzn7tmtBZWlqdE UDGBXB070OjHFACQ== Date: Fri, 13 Nov 2020 15:02:26 +0100 From: Thomas Gleixner To: LKML Cc: Peter Zijlstra , Frederic Weisbecker , Paul McKenney , Sebastian Andrzej Siewior , Arnd Bergmann , "James E.J. Bottomley" , Helge Deller , linux-parisc@vger.kernel.org, Yoshinori Sato , Rich Felker , linux-sh@vger.kernel.org, Jeff Dike , Richard Weinberger , Anton Ivanov , linux-um@lists.infradead.org, Russell King , Marc Zyngier , Valentin Schneider , linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon Subject: [patch 19/19] tasklets: Prevent kill/unlock_wait deadlock on RT References: <20201113140207.499353218@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-transfer-encoding: 8-bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org tasklet_kill() and tasklet_unlock_wait() spin and wait for the TASKLET_STATE_SCHED resp. TASKLET_STATE_RUN bit in the tasklet state to be cleared. This works on !RT nicely because the corresponding execution can only happen on a different CPU. On RT softirq processing is preemptible, therefore a task preempting the softirq processing thread can spin forever. Prevent this by invoking local_bh_disable()/enable() inside the loop. In case that the softirq processing thread was preempted by the current task, current will block on the local lock which yields the CPU to the preempted softirq processing thread. If the tasklet is processed on a different CPU then the local_bh_disable()/enable() pair is just a waste of processor cycles. Signed-off-by: Thomas Gleixner --- include/linux/interrupt.h | 8 ++------ kernel/softirq.c | 38 +++++++++++++++++++++++++++++++++++++- 2 files changed, 39 insertions(+), 7 deletions(-) --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -654,7 +654,7 @@ enum TASKLET_STATE_RUN /* Tasklet is running (SMP only) */ }; -#ifdef CONFIG_SMP +#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT) static inline int tasklet_trylock(struct tasklet_struct *t) { return !test_and_set_bit(TASKLET_STATE_RUN, &(t)->state); @@ -666,11 +666,7 @@ static inline void tasklet_unlock(struct clear_bit(TASKLET_STATE_RUN, &(t)->state); } -static inline void tasklet_unlock_wait(struct tasklet_struct *t) -{ - while (test_bit(TASKLET_STATE_RUN, &(t)->state)) - cpu_relax(); -} +void tasklet_unlock_wait(struct tasklet_struct *t); #else static inline int tasklet_trylock(struct tasklet_struct *t) { return 1; } static inline void tasklet_unlock(struct tasklet_struct *t) { } --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -851,6 +851,29 @@ void tasklet_init(struct tasklet_struct } EXPORT_SYMBOL(tasklet_init); +#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT) + +void tasklet_unlock_wait(struct tasklet_struct *t) +{ + while (test_bit(TASKLET_STATE_RUN, &(t)->state)) { + if (IS_ENABLED(CONFIG_PREEMPT_RT)) { + /* + * Prevent a live lock when current preempted soft + * interrupt processing or prevents ksoftirqd from + * running. If the tasklet runs on a different CPU + * then this has no effect other than doing the BH + * disable/enable dance for nothing. + */ + local_bh_disable(); + local_bh_enable(); + } else { + cpu_relax(); + } + } +} +EXPORT_SYMBOL(tasklet_unlock_wait); +#endif + void tasklet_kill(struct tasklet_struct *t) { if (in_interrupt()) @@ -858,7 +881,20 @@ void tasklet_kill(struct tasklet_struct while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) { do { - yield(); + if (IS_ENABLED(CONFIG_PREEMPT_RT)) { + /* + * Prevent a live lock when current + * preempted soft interrupt processing or + * prevents ksoftirqd from running. If the + * tasklet runs on a different CPU then + * this has no effect other than doing the + * BH disable/enable dance for nothing. + */ + local_bh_disable(); + local_bh_enable(); + } else { + yield(); + } } while (test_bit(TASKLET_STATE_SCHED, &t->state)); } tasklet_unlock_wait(t);