From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757473AbaDWIKh (ORCPT ); Wed, 23 Apr 2014 04:10:37 -0400 Received: from www.linutronix.de ([62.245.132.108]:53646 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752435AbaDWIK0 (ORCPT ); Wed, 23 Apr 2014 04:10:26 -0400 Message-ID: <53577559.9090501@linutronix.de> Date: Wed, 23 Apr 2014 10:10:01 +0200 From: Sebastian Andrzej Siewior User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Icedove/24.4.0 MIME-Version: 1.0 To: Peter Zijlstra , Steven Rostedt CC: Stanislav Meduna , "linux-rt-users@vger.kernel.org" , Linux ARM Kernel , "linux-kernel@vger.kernel.org" , Thomas Gleixner Subject: Re: BUG: spinlock trylock failure on UP, i.MX28 3.12.15-rt25 References: <534C3606.7010206@meduna.org> <534C731F.1050406@meduna.org> <534DADF1.6060608@meduna.org> <20140422115439.GA20669@linutronix.de> <20140422094657.5b6ca1e2@gandalf.local.home> <20140422140918.GE11096@twins.programming.kicks-ass.net> In-Reply-To: <20140422140918.GE11096@twins.programming.kicks-ass.net> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/22/2014 04:09 PM, Peter Zijlstra wrote: > On Tue, Apr 22, 2014 at 09:46:57AM -0400, Steven Rostedt wrote: >>> According to lockdep a trylock should not fail on UP. > > Oh!? Where does it say that? A trylock can fail at all times. kernel/locking/spinlock_debug.c: int do_raw_spin_trylock(raw_spinlock_t *lock) { int ret = arch_spin_trylock(&lock->raw_lock); if (ret) debug_spin_lock_after(lock); #ifndef CONFIG_SMP /* * Must not happen on UP: */ SPIN_BUG_ON(!ret, lock, "trylock failure on UP"); #endif return ret; } How can a trylock (spinlock, not mutex) fail on UP? That would mean the lock is not interrupt safe. Unless, you attempt to take the lock from interrupt context via trylock while in general you take the spinlock in process context with interrupts enabled. Sebastian From mboxrd@z Thu Jan 1 00:00:00 1970 From: bigeasy@linutronix.de (Sebastian Andrzej Siewior) Date: Wed, 23 Apr 2014 10:10:01 +0200 Subject: BUG: spinlock trylock failure on UP, i.MX28 3.12.15-rt25 In-Reply-To: <20140422140918.GE11096@twins.programming.kicks-ass.net> References: <534C3606.7010206@meduna.org> <534C731F.1050406@meduna.org> <534DADF1.6060608@meduna.org> <20140422115439.GA20669@linutronix.de> <20140422094657.5b6ca1e2@gandalf.local.home> <20140422140918.GE11096@twins.programming.kicks-ass.net> Message-ID: <53577559.9090501@linutronix.de> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 04/22/2014 04:09 PM, Peter Zijlstra wrote: > On Tue, Apr 22, 2014 at 09:46:57AM -0400, Steven Rostedt wrote: >>> According to lockdep a trylock should not fail on UP. > > Oh!? Where does it say that? A trylock can fail at all times. kernel/locking/spinlock_debug.c: int do_raw_spin_trylock(raw_spinlock_t *lock) { int ret = arch_spin_trylock(&lock->raw_lock); if (ret) debug_spin_lock_after(lock); #ifndef CONFIG_SMP /* * Must not happen on UP: */ SPIN_BUG_ON(!ret, lock, "trylock failure on UP"); #endif return ret; } How can a trylock (spinlock, not mutex) fail on UP? That would mean the lock is not interrupt safe. Unless, you attempt to take the lock from interrupt context via trylock while in general you take the spinlock in process context with interrupts enabled. Sebastian