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Mon, 7 May 2018 14:21:22 -0400 Received: from mail.kernel.org ([198.145.29.99]:54164 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752352AbeEGSVV (ORCPT ); Mon, 7 May 2018 14:21:21 -0400 Date: Mon, 7 May 2018 14:21:17 -0400 From: Steven Rostedt To: Joel Fernandes Cc: 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 , kernel-team@android.com, stable@vger.kernel.org Subject: Re: [PATCH] softirq: reorder trace_softirqs_on to prevent lockdep splat Message-ID: <20180507142117.35310ff2@gandalf.local.home> In-Reply-To: <20180502014439.87828-1-joelaf@google.com> References: <20180502014439.87828-1-joelaf@google.com> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: Peter, Ingo or Thomas, Can you queue this up? Or would you prefer that I take it? -- Steve On Tue, 1 May 2018 18:44:39 -0700 Joel Fernandes wrote: > 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: 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 > 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 > --- > kernel/softirq.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/kernel/softirq.c b/kernel/softirq.c > index 24d243ef8e71..47e2f61938c0 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); > } > > /*