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 C6D00C388F7 for ; Fri, 13 Nov 2020 14:24:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8BBD422240 for ; Fri, 13 Nov 2020 14:24:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="G1UREJyG"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="Qk1c/61D" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726983AbgKMOYn (ORCPT ); Fri, 13 Nov 2020 09:24:43 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:52700 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726894AbgKMOYe (ORCPT ); Fri, 13 Nov 2020 09:24:34 -0500 Message-Id: <20201113141734.442990268@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1605277472; 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=Ze6MlncdnmAY8gfHx7Z+rZEVhWAMCevnsPTsGbdb6v0=; b=G1UREJyGcaUjT+N2wtoQyCERcLxyjyMAfw8NfT+wy0zwm0us+pf2Ntglv96NgSHbt9/Yjp qoaQCmQHCEZLSl4tgh2fObbzd5Eg0IzKsZOwRDqSmqku7HiNL3S3LkyTYUFx3yi5dSfTxu MFctcDrCS9gok9I097XT39eWW13m7iPU863iXCxWWkLue2i4sFBBOxeCX2J3FMIX3WJFOU XfnbdSiKjTIyQx4waIuiaRF6W5mUn7JksZs9HbxgKcANUpu5giQHMT3WvlrsVLnuu9ttOJ 05xVo+iYIedu+Z/p/XcxdBOfYtlbWlAMcmQFwZfDQFcdF0rqvP2z6Iy7H5Dc2A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1605277472; 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=Ze6MlncdnmAY8gfHx7Z+rZEVhWAMCevnsPTsGbdb6v0=; b=Qk1c/61DOVl3kFFVW+aZ3dXfkp84eaNY2QVxxJLj8d6ltQSfXPHHs0VNAwsQ94XeTMC/Dx 80Ju8vg9dueyHvAQ== Date: Fri, 13 Nov 2020 15:02:22 +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 15/19] tick/sched: Prevent false positive softirq pending warnings 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 On RT a task which has soft interrupts disabled can block on a lock and schedule out to idle while soft interrupts are pending. This triggers the warning in the NOHZ idle code which complains about going idle with pending soft interrupts. But as the task is blocked soft interrupt processing is temporarily blocked as well which means that such a warning is a false positive. To prevent that check the per CPU state which indicates that a scheduled out task has soft interrupts disabled. Signed-off-by: Thomas Gleixner --- include/linux/bottom_half.h | 6 ++++++ kernel/softirq.c | 15 +++++++++++++++ kernel/time/tick-sched.c | 2 +- 3 files changed, 22 insertions(+), 1 deletion(-) --- a/include/linux/bottom_half.h +++ b/include/linux/bottom_half.h @@ -32,4 +32,10 @@ static inline void local_bh_enable(void) __local_bh_enable_ip(_THIS_IP_, SOFTIRQ_DISABLE_OFFSET); } +#ifdef CONFIG_PREEMPT_RT +extern bool local_bh_blocked(void); +#else +static inline bool local_bh_blocked(void) { return false; } +#endif + #endif /* _LINUX_BH_H */ --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -138,6 +138,21 @@ static DEFINE_PER_CPU(struct softirq_ctr .lock = INIT_LOCAL_LOCK(softirq_ctrl.lock), }; +/** + * local_bh_blocked() - Check for idle whether BH processing is blocked + * + * Returns false if the per CPU softirq::cnt is 0 otherwise true. + * + * This is invoked from the idle task to guard against false positive + * softirq pending warnings, which would happen when the task which holds + * softirq_ctrl::lock was the only running task on the CPU and blocks on + * some other lock. + */ +bool local_bh_blocked(void) +{ + return this_cpu_read(softirq_ctrl.cnt) != 0; +} + void __local_bh_disable_ip(unsigned long ip, unsigned int cnt) { unsigned long flags; --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -925,7 +925,7 @@ static bool can_stop_idle_tick(int cpu, if (unlikely(local_softirq_pending())) { static int ratelimit; - if (ratelimit < 10 && + if (ratelimit < 10 && !local_bh_blocked() && (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) { pr_warn("NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #%02x!!!\n", (unsigned int) local_softirq_pending());