From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755362AbYGIWqr (ORCPT ); Wed, 9 Jul 2008 18:46:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752018AbYGIWqj (ORCPT ); Wed, 9 Jul 2008 18:46:39 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:43928 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751593AbYGIWqi (ORCPT ); Wed, 9 Jul 2008 18:46:38 -0400 Date: Thu, 10 Jul 2008 00:46:37 +0200 From: Jan Kara To: Andrew Morton Cc: Arjan van de Ven , linux-kernel@vger.kernel.org, Al Viro Subject: Re: Kernel oops (bug) in fs/buffers.c:create_empty_buffers Message-ID: <20080709224637.GA30008@atrey.karlin.mff.cuni.cz> References: <20080706132302.5ca87f4f@infradead.org> <20080706133100.8d8ed269.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080706133100.8d8ed269.akpm@linux-foundation.org> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Sun, 6 Jul 2008 13:23:02 -0700 Arjan van de Ven wrote: > > Hi, > > > > caught this one on kerneloops.org: > > http://www.kerneloops.org/searchweek.php?search=create_empty_buffers > > > > void create_empty_buffers(struct page *page, > > unsigned long blocksize, unsigned long b_state) > > { > > struct buffer_head *bh, *head, *tail; > > > > head = alloc_page_buffers(page, blocksize, 1); > > bh = head; > > do { > > bh->b_state |= b_state; > > tail = bh; > > bh = bh->b_this_page; > > } while (bh); > > > > > > turns out, alloc_page_buffers() can fail and return NULL (for AIO for > > example)... yet this code blindly dereferences the result, getting a > > predictable NULL pointer fault. > > > > It's not directly clear what to do about... make this function return > > the failure to the caller? > > isofs has a habit of returning impossible block sizes and the > > while ((offset -= size) >= 0) { > > consequently loops zero times and alloc_page_buffers() returns null. > > Someone was having a look at it - maybe Jan? Yes, I was looking at that. Actually, I've pinpointed the cause of the Oopses I've seen to a bug in ide-cd driver. It happily sets blocksize to whatever value the drive reported and some drives have a habit of reporting bogus values when unreadable medium is inserted. Jens has actually cooked up a fix for this bug (http://thread.gmane.org/gmane.linux.kernel/696582) and it fixes the problem at least for me. > I assume that the kernloops.org records link back to the original > report somewhere but I can't find it? Honza -- Jan Kara SuSE CR Labs