From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753473AbaDWMPd (ORCPT ); Wed, 23 Apr 2014 08:15:33 -0400 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.226]:34711 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752652AbaDWMPc (ORCPT ); Wed, 23 Apr 2014 08:15:32 -0400 Date: Wed, 23 Apr 2014 08:15:25 -0400 From: Steven Rostedt To: Sebastian Andrzej Siewior Cc: Stanislav Meduna , "linux-rt-users@vger.kernel.org" , Linux ARM Kernel , "linux-kernel@vger.kernel.org" , Thomas Gleixner , Peter Zijlstra Subject: Re: BUG: spinlock trylock failure on UP, i.MX28 3.12.15-rt25 Message-ID: <20140423081525.0e9b863f@gandalf.local.home> In-Reply-To: <53576859.8060706@linutronix.de> References: <534C3606.7010206@meduna.org> <534C731F.1050406@meduna.org> <534DADF1.6060608@meduna.org> <20140422115439.GA20669@linutronix.de> <20140422094657.5b6ca1e2@gandalf.local.home> <53569E05.8010600@linutronix.de> <20140422134802.73fc1fa4@gandalf.local.home> <20140422141650.7f43d5ba@gandalf.local.home> <53576859.8060706@linutronix.de> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.22; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-RR-Connecting-IP: 107.14.168.118:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 23 Apr 2014 09:14:33 +0200 Sebastian Andrzej Siewior wrote: > On 04/22/2014 08:16 PM, Steven Rostedt wrote: > > --- a/kernel/timer.c > > +++ b/kernel/timer.c > > @@ -1447,6 +1447,12 @@ static void run_timer_softirq(struct softirq_action *h) > > __run_timers(base); > > } > > > > +#ifdef CONFIG_SMP > > +#define timer_should_raise_softirq(lock) !spin_do_trylock(lock) > > +#else > > +#define timer_should_raise_softirq(lock) 1 > > +#endif > > + > > No. The lock may be taken but it also may be available no matter if UP > or not. With this patch applied the lockdep splat will go away but the > FULL_NO_HZ people will come back because the timer softirq is scheduled > even if no timer has expired. Although, as Peter said FULL_NO_HZ is pretty pointless on UP, but I've been thinking this from a non PREEMPT_RT viewpoint. In non PREEMPT_RT, spin_locks() are nops, where this is an issue, but in PREEMPT_RT, they are mutexes, BUT! The rt_mutex use wait_lock to protect its internal state, which is a raw spinlock, and in UP it's a nop. That means there's nothing preventing an interrupt here from corrupting the rtmutex's internal state. I see this is still an issue, and the warning is still valid. -- Steve