Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261238AbVCTQ6Q (ORCPT ); Sun, 20 Mar 2005 11:58:16 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261240AbVCTQ6Q (ORCPT ); Sun, 20 Mar 2005 11:58:16 -0500 Received: from dbl.q-ag.de ([213.172.117.3]:31455 "EHLO dbl.q-ag.de") by vger.kernel.org with ESMTP id S261238AbVCTQ6L (ORCPT ); Sun, 20 Mar 2005 11:58:11 -0500 Message-ID: <423DAB73.2030904@colorfullife.com> Date: Sun, 20 Mar 2005 17:57:23 +0100 From: Manfred Spraul User-Agent: Mozilla/5.0 (X11; U; Linux i686; fr-FR; rv:1.7.3) Gecko/20041020 X-Accept-Language: en-us, en MIME-Version: 1.0 To: tglx@linutronix.de CC: Ingo Molnar , "Paul E. McKenney" , dipankar@in.ibm.com, shemminger@osdl.org, Andrew Morton , Linus Torvalds , rusty@au1.ibm.com, tgall@us.ibm.com, jim.houston@comcast.net, gh@us.ibm.com, LKML Subject: Re: Real-Time Preemption and RCU References: <20050318002026.GA2693@us.ibm.com> <20050318091303.GB9188@elte.hu> <20050318092816.GA12032@elte.hu> <423BB299.4010906@colorfullife.com> <20050319162601.GA28958@elte.hu> <423D19FE.7020902@colorfullife.com> <1111310736.17944.24.camel@tglx.tec.linutronix.de> In-Reply-To: <1111310736.17944.24.camel@tglx.tec.linutronix.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1257 Lines: 48 Thomas Gleixner wrote: >On Sun, 2005-03-20 at 07:36 +0100, Manfred Spraul wrote: > > >>cpu 1: >>acquire random networking spin_lock_bh() >> >>cpu 2: >>read_lock(&tasklist_lock) from process context >>interrupt. softirq. within softirq: try to acquire the networking lock. >>* spins. >> >>cpu 1: >>hardware interrupt >>within hw interrupt: signal delivery. tries to acquire tasklist_lock. >> >>--> deadlock. >> >> > >Signal delivery from hw interrupt context (interrupt is flagged >SA_NODELAY) is not possible in RT preemption mode. The >local_irq_save_nort() check in __cache_alloc will catch you. > > > That was just one random example. Another one would be : drivers/chat/tty_io.c, __do_SAK() contains read_lock(&tasklist_lock); task_lock(p); kernel/sys.c, sys_setrlimit contains task_lock(current->group_leader); read_lock(&tasklist_lock); task_lock is a shorthand for spin_lock(&p->alloc_lock). If read_lock is a normal spinlock, then this is an A/B B/A deadlock. -- Manfred - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/