From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751455AbeD0ELT (ORCPT ); Fri, 27 Apr 2018 00:11:19 -0400 Received: from mail-pg0-f66.google.com ([74.125.83.66]:32970 "EHLO mail-pg0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750877AbeD0ELS (ORCPT ); Fri, 27 Apr 2018 00:11:18 -0400 X-Google-Smtp-Source: AB8JxZq7Kph7w7uHBj8I5st1F1hLGlz0EGGvmGmdiRQxouM+LmVteBYo9w9DC5GB9+53HiCd5xyo0g== From: Joel Fernandes To: linux-kernel@vger.kernel.org Cc: Joel Fernandes , Steven Rostedt , 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 , kernel-team@android.com Subject: [PATCH] softirq: reorder trace_softirqs_on to prevent lockdep splat Date: Thu, 26 Apr 2018 21:11:00 -0700 Message-Id: <20180427041100.133772-1-joelaf@google.com> X-Mailer: git-send-email 2.17.0.441.gb46fe60e1d-goog Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I'm able to reproduce a lockdep splat when CONFIG_PROVE_LOCKING=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 problem is the softirqs annotation in lockdep goes out of sync with the reality of the world that softirq is still off. This causes a lockdep splat because the preempt_count_sub can call into a preemptoff tracer or the trace events code, which inturn can call into lockdep *before* softirqs are really turned back on, which can cause a softirqs invalid annotation splat in lockdep. The same issue was fixed in local_bh_disable_ip which has a comment so: /* * The preempt tracer hooks into preempt_count_add and will break * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET * is set and before current->softirq_enabled is cleared. * We must manually increment preempt_count here and manually * call the trace_preempt_off later. */ I have done a similar change to the local_bh_enable path to fix it. Cc: Steven Rostedt Cc: Peter Zilstra Cc: Ingo Molnar Cc: Mathieu Desnoyers Cc: Tom Zanussi Cc: Namhyung Kim Cc: Thomas Glexiner Cc: Boqun Feng Cc: Paul McKenney Cc: Frederic Weisbecker Cc: Randy Dunlap Cc: Masami Hiramatsu Cc: Fenguang Wu Cc: Baohong Liu Cc: Vedang Patel Cc: kernel-team@android.com Signed-off-by: Joel Fernandes --- 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); } /* -- 2.17.0.441.gb46fe60e1d-goog