From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Rostedt Subject: Re: BUG: spinlock trylock failure on UP, i.MX28 3.12.15-rt25 Date: Tue, 22 Apr 2014 09:46:57 -0400 Message-ID: <20140422094657.5b6ca1e2@gandalf.local.home> References: <534C3606.7010206@meduna.org> <534C731F.1050406@meduna.org> <534DADF1.6060608@meduna.org> <20140422115439.GA20669@linutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Stanislav Meduna , "linux-rt-users@vger.kernel.org" , Linux ARM Kernel , "linux-kernel@vger.kernel.org" , Thomas Gleixner , Peter Zijlstra To: Sebastian Andrzej Siewior Return-path: In-Reply-To: <20140422115439.GA20669@linutronix.de> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-rt-users.vger.kernel.org [ added Peter ] On Tue, 22 Apr 2014 13:54:39 +0200 Sebastian Andrzej Siewior wrote: =20 > this is, erm, harmless. We grab the timer lock via trylock in hardirq > context. If the lock is already taken then we fail to get it we go fo= r > plan B. According to lockdep a trylock should not fail on UP. This is > true in general except for this timer case. I was thinking abour > disabling this lockdep check=E2=80=A6 trylock not failing on UP, can that be an issue? I mean, if a hardirq does a trylock to see if it can grab a lock that is not protected by disabling irqs, and will go to plan B if it fails, on UP, it will always get it. But the issue is still there. That would mean that a hardirq could have preempted a critical section and doing a trylock here would succeed when it really should have failed. -- Steve