From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751753AbeFAEwc (ORCPT ); Fri, 1 Jun 2018 00:52:32 -0400 Received: from mail-pf0-f195.google.com ([209.85.192.195]:46746 "EHLO mail-pf0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751444AbeFAEwS (ORCPT ); Fri, 1 Jun 2018 00:52:18 -0400 X-Google-Smtp-Source: ADUXVKLcFiq4cSg6DW87YyEOZcjndbSZcOHCF0OAvJptv+SkOfMUe50Mk/orb1sUdxflcc7C/BTNAg== Date: Thu, 31 May 2018 21:52:15 -0700 From: Joel Fernandes To: Steven Rostedt Cc: Joel Fernandes , linux-kernel@vger.kernel.org, Peter Zilstra , Ingo Molnar , Mathieu Desnoyers , Tom Zanussi , Namhyung Kim , Thomas Glexiner , Boqun Feng , Paul McKenney , Frederic Weisbecker , Randy Dunlap , Masami Hiramatsu , Fenguang Wu , Baohong Liu , Vedang Patel , stable@vger.kernel.org Subject: Re: [PATCH] softirq: reorder trace_softirqs_on to prevent lockdep splat Message-ID: <20180601045215.GA168630@joelaf.mtv.corp.google.com> References: <20180502014439.87828-1-joelaf@google.com> <20180507142117.35310ff2@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180507142117.35310ff2@gandalf.local.home> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 07, 2018 at 02:21:17PM -0400, Steven Rostedt wrote: > Peter, Ingo or Thomas, > > Can you queue this up? Or would you prefer that I take it? This patch is a bug fix, could it be queued for v4.17 -rc cycle or for linux-next? I have also included it below again: thanks, - Joel ---8<----------------------- From: "Joel Fernandes (Google)" Date: Tue, 1 May 2018 18:44:39 -0700 Subject: [PATCH] softirq: reorder trace_softirqs_on to prevent lockdep splat I'm able to reproduce a lockdep splat with config options: CONFIG_PROVE_LOCKING=y, CONFIG_DEBUG_LOCK_ALLOC=y and CONFIG_PREEMPTIRQ_EVENTS=y $ echo 1 > /d/tracing/events/preemptirq/preempt_enable/enable [ 26.112609] DEBUG_LOCKS_WARN_ON(current->softirqs_enabled) [ 26.112636] WARNING: CPU: 0 PID: 118 at kernel/locking/lockdep.c:3854 [...] [ 26.144229] Call Trace: [ 26.144926] [ 26.145506] lock_acquire+0x55/0x1b0 [ 26.146499] ? __do_softirq+0x46f/0x4d9 [ 26.147571] ? __do_softirq+0x46f/0x4d9 [ 26.148646] trace_preempt_on+0x8f/0x240 [ 26.149744] ? trace_preempt_on+0x4d/0x240 [ 26.150862] ? __do_softirq+0x46f/0x4d9 [ 26.151930] preempt_count_sub+0x18a/0x1a0 [ 26.152985] __do_softirq+0x46f/0x4d9 [ 26.153937] irq_exit+0x68/0xe0 [ 26.154755] smp_apic_timer_interrupt+0x271/0x280 [ 26.156056] apic_timer_interrupt+0xf/0x20 [ 26.157105] The issue was this: preempt_count = 1 << SOFTIRQ_SHIFT __local_bh_enable(cnt = 1 << SOFTIRQ_SHIFT) { if (softirq_count() == (cnt && SOFTIRQ_MASK)) { trace_softirqs_on() { current->softirqs_enabled = 1; } } preempt_count_sub(cnt) { trace_preempt_on() { tracepoint() { rcu_read_lock_sched() { // jumps into lockdep Where preempt_count still has softirqs disabled, but current->softirqs_enabled is true, and we get a splat. Cc: stable@vger.kernel.org Reviewed-by: Steven Rostedt (VMware) Fixes: d59158162e032 ("tracing: Add support for preempt and irq enable/disable events") Signed-off-by: Joel Fernandes (Google) --- kernel/softirq.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/softirq.c b/kernel/softirq.c index 177de3640c78..8a040bcaa033 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -139,9 +139,13 @@ static void __local_bh_enable(unsigned int cnt) { lockdep_assert_irqs_disabled(); + if (preempt_count() == cnt) + trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip()); + if (softirq_count() == (cnt & SOFTIRQ_MASK)) trace_softirqs_on(_RET_IP_); - preempt_count_sub(cnt); + + __preempt_count_sub(cnt); } /* -- 2.17.0.921.gf22659ad46-goog