From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751980AbeDQEIS (ORCPT ); Tue, 17 Apr 2018 00:08:18 -0400 Received: from mail-pg0-f66.google.com ([74.125.83.66]:33727 "EHLO mail-pg0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750744AbeDQEIN (ORCPT ); Tue, 17 Apr 2018 00:08:13 -0400 X-Google-Smtp-Source: AIpwx4+5YTeDK24ziZvmYfgAPdyE6Xnp2BrgE1PL1wwNCIkY1JDaVa+w0RaUBems4R+RAr8AIRYv+Q== From: Joel Fernandes To: linux-kernel@vger.kernel.org, linux-rt-users@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 Subject: [RFC v4 2/4] softirq: reorder trace_softirqs_on to prevent lockdep splat Date: Mon, 16 Apr 2018 21:07:46 -0700 Message-Id: <20180417040748.212236-3-joelaf@google.com> X-Mailer: git-send-email 2.17.0.484.g0c8726318c-goog In-Reply-To: <20180417040748.212236-1-joelaf@google.com> References: <20180417040748.212236-1-joelaf@google.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently there's an issue which is not always reproducible, where the softirqs annotation in lockdep goes out of sync with the reality of the world and causes a lockdep splat. This is because the preemptoff tracer calls into lockdep which can cause a softirqs invalid annotation splat. The same issue was fixed in local_bh_disable_ip. /* * 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 am not fully sure why the issue is reproducible with my patches easily, but it seems like the same ordering issue can exist so we ought 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 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); } /* -- 2.17.0.484.g0c8726318c-goog