Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936084AbXJQRxf (ORCPT ); Wed, 17 Oct 2007 13:53:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758221AbXJQRx2 (ORCPT ); Wed, 17 Oct 2007 13:53:28 -0400 Received: from smtp2.linux-foundation.org ([207.189.120.14]:51880 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757309AbXJQRx1 (ORCPT ); Wed, 17 Oct 2007 13:53:27 -0400 Date: Wed, 17 Oct 2007 10:52:13 -0700 (PDT) From: Linus Torvalds To: Jens Axboe cc: Ingo Molnar , linux-kernel@vger.kernel.org, Andrew Morton Subject: Re: [bug] block subsystem related crash with latest -git In-Reply-To: <20071017170804.GG15552@kernel.dk> Message-ID: References: <20071017154655.GA13394@elte.hu> <20071017165949.GF15552@kernel.dk> <20071017170804.GG15552@kernel.dk> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1959 Lines: 48 On Wed, 17 Oct 2007, Jens Axboe wrote: > > OK, the below should actually be safe, I don't know why I talked myself > into the next_sg stuff in the beginning. It's always safe to zero sg, > since it's a valid entry - nothing to save in ->page. Ingo, does this > work for you? I really don't think this should work. Doing "sg_next()" on a valid sg is *always* ok. So if the old code didn't work, then "sg" wasn't valid to start with (and the code *after* the sg_next() would have oopsed even if you try to avoid using sg_next. So avoiding the "sg_next()" on the last entry is pointless. Also, your patch makes the code almost totally unreadable, with that subtle issue of the "if (bvprv && cluster)" case not triggering on the first case, so the NULL initial sg is "safe". So at a guess, I think the *real* problem is simply that the passed-in sglist was just too small. What guarantees that the sg list allocation (apparently done by scsi_alloc_sgtable()) is big enough? If I read things right, scsi_alloc_sgtable() will allocate "cmd->use_sg" SG enties, no? But I also notice that it does not seem to initialize the SG allocation, so those SG entries contain random crap - including, perhaps, a random - and bogus - chain pointer in sg->page.. Yes, we set sh->page *if* we create a chain, but if we don't chain, we leave the old random contents around which in turn may include old and stale chain pointers. Or am I missing something? So when you added that "memset(sg, 0, sizeof(*sg))" into blk_rq_map_sg(), you did it way too late - it needs to be done when the sg chain is allocated, and for every entry (and then the "link" entry needs to be linked in separately) I think. Linus - 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/