Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757654AbYAWRf1 (ORCPT ); Wed, 23 Jan 2008 12:35:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757209AbYAWRc4 (ORCPT ); Wed, 23 Jan 2008 12:32:56 -0500 Received: from tomts20-srv.bellnexxia.net ([209.226.175.74]:48002 "EHLO tomts20-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755597AbYAWRcy (ORCPT ); Wed, 23 Jan 2008 12:32:54 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Ao8CAKQIl0dMQWYq/2dsb2JhbACBV6xk Date: Wed, 23 Jan 2008 12:32:49 -0500 From: Mathieu Desnoyers To: Steven Rostedt Cc: Daniel Walker , LKML , Ingo Molnar , Linus Torvalds , Andrew Morton , Peter Zijlstra , Christoph Hellwig , Gregory Haskins , Arnaldo Carvalho de Melo , Thomas Gleixner , Tim Bird , Sam Ravnborg , "Frank Ch. Eigler" , Jan Kiszka , John Stultz , Arjan van de Ven , Steven Rostedt Subject: Re: [PATCH 01/20 -v5] printk - dont wakeup klogd with interrupts disabled Message-ID: <20080123173249.GA23503@Krystal> References: <20080123160236.969334052@goodmis.org> <20080123160441.236562634@goodmis.org> <1201107978.13596.16.camel@imap.mvista.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 12:29:31 up 80 days, 22:34, 5 users, load average: 0.56, 0.46, 0.40 User-Agent: Mutt/1.5.16 (2007-06-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2606 Lines: 105 * Steven Rostedt (rostedt@goodmis.org) wrote: > > On Wed, 23 Jan 2008, Daniel Walker wrote: > > > > > On Wed, 2008-01-23 at 11:02 -0500, Steven Rostedt wrote: > > > > > + if (!irqs_disabled() && wake_klogd) > > > wake_up_klogd(); > > > > This causes a regression .. When printk is called during an OOPS in > > kernels without this change then the OOPS will get logged, since the > > logging process (klogd) is woken to handle the messages.. If you apply > > this change klogd doesn't wakeup, and hence doesn't log the oops.. So if > > you remove the wakeup here you have to add it someplace else to maintain > > the logging .. > > > > (I'm not theorizing here, I have defects logged against this specific > > piece of code..) > > It wont get woken up anyway. Did you look at wake_up_klogd? > > void wake_up_klogd(void) > { > if (!oops_in_progress && waitqueue_active(&log_wait)) > wake_up_interruptible(&log_wait); > } > > > So if oops_in_progress is set, then it still wont get woken. Perhaps it > got woken some other way? Or is oops_in_progress not set in these oops? > > One other solution is to make the runqueue locks visible externally. Like: > > in sched.c: > > int runqueue_is_locked(void) > { > int cpu = get_cpu(); > struct rq *rq = cpu_rq(cpu); > int ret; > > ret = spin_is_locked(&rq->lock); > put_cpu(); > return ret; > } > > And in printk we could do: > > if (wake_klogd && !runqueue_is_locked()) > wake_up_klogd(); > > This probably is the cleanest solution since it simply prevents the > deadlock from occurring. > FYI : kernel/panic.c NORET_TYPE void panic(const char * fmt, ...) { .... bust_spinlocks(1); ... bust_spinlocks(0); ... In bust_spinlocks : void __attribute__((weak)) bust_spinlocks(int yes) { if (yes) { ++oops_in_progress; } else { #ifdef CONFIG_VT unblank_screen(); #endif if (--oops_in_progress == 0) wake_up_klogd(); } } Where the final wake_up happens while oops_in_progress is 0, but interrupts are still disabled. So about my previous email, proposing testing oops_in_progress, it just won't work. Mathieu > -- Steve > -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 -- 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/