From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756570Ab2DYQ02 (ORCPT ); Wed, 25 Apr 2012 12:26:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:64373 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756153Ab2DYQ0Y convert rfc822-to-8bit (ORCPT ); Wed, 25 Apr 2012 12:26:24 -0400 From: Jeff Moyer To: =?utf-8?Q?J=C3=B6rn?= Engel Cc: linux-kernel@vger.kernel.org Subject: Re: [RFC][PATCH] add blockconsole References: <20120424205946.GH20610@logfs.org> <20120425132513.GA23492@logfs.org> X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 X-PCLoadLetter: What the f**k does that mean? Date: Wed, 25 Apr 2012 11:52:28 -0400 In-Reply-To: <20120425132513.GA23492@logfs.org> (=?utf-8?Q?=22J=C3=B6rn?= Engel"'s message of "Wed, 25 Apr 2012 09:25:14 -0400") Message-ID: User-Agent: Gnus/5.110011 (No Gnus v0.11) Emacs/23.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jörn Engel writes: > On Wed, 25 April 2012 09:42:39 -0400, Jeff Moyer wrote: >> >> Neat idea, but I'm curious to know how it works when the system panics >> and you no longer can schedule the writeback thread. What are the >> limitations you've seen in practice? > > If the writeback thread doesn't get scheduled, you lose that > information. Formerly I did the submit_bio directly, but lockdep > reminded me that I shouldn't do so from interrupt context. Bummer. Well, submit_bio can sleep, obviously. Perhaps you could explore registering a panic notifier, and then flush the logs from there? Unfortunately, there is always the possibility that some required locks will be taken, but it might get you a little bit further. Or, you could explore the route that the diskdump or lkcd folks took, implementing their own polling mode drivers. Cheers, Jeff