Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751357AbaDWVjp (ORCPT ); Wed, 23 Apr 2014 17:39:45 -0400 Received: from cantor2.suse.de ([195.135.220.15]:42131 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751017AbaDWVjo (ORCPT ); Wed, 23 Apr 2014 17:39:44 -0400 Date: Wed, 23 Apr 2014 23:39:43 +0200 (CEST) From: Jiri Kosina X-X-Sender: jikos@twin.jikos.cz To: Andrew Morton cc: Rik van Riel , linux-kernel@vger.kernel.org, joern@logfs.org, peterz@infradead.org, cxie@redhat.com, Greg Kroah-Hartman , Jiri Slaby Subject: Re: [PATCH RFC] sysrq: rcu-ify __handle_sysrq In-Reply-To: <20140423130453.32361ca9ceef591b9b184926@linux-foundation.org> Message-ID: References: <20140423125352.704f9fb2@annuminas.surriel.com> <20140423130453.32361ca9ceef591b9b184926@linux-foundation.org> User-Agent: Alpine 2.00 (LRH 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 23 Apr 2014, Andrew Morton wrote: > > Echoing values into /proc/sysrq-trigger seems to be a popular way to > > get information out of the kernel. However, dumping information about > > thousands of processes, or hundreds of CPUs to serial console can > > result in IRQs being blocked for minutes, resulting in various kinds > > of cascade failures. > > > > The most common failure is due to interrupts being blocked for a very > > long time. This can lead to things like failed IO requests, and other > > things the system cannot easily recover from. > > I bet nobody wants that console output anyway. You do the sysrq then > run dmesg or look in /var/log/messages to see what happened. People > who are experiencing problems such as this should run `dmesg -n 1' > before writing to sysrq-trigger. I don't agree. I have used sysrq-t multiple times in situations where userspace was already dead, but sysrq was still able to provide valuable information about the state of the kernel. -- Jiri Kosina SUSE Labs -- 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/