From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751637Ab2IRQcR (ORCPT ); Tue, 18 Sep 2012 12:32:17 -0400 Received: from mx1.redhat.com ([209.132.183.28]:17801 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750992Ab2IRQcO (ORCPT ); Tue, 18 Sep 2012 12:32:14 -0400 Date: Tue, 18 Sep 2012 17:31:57 +0100 From: Alasdair G Kergon To: Kent Overstreet Cc: linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com, Jens Axboe , Lars Ellenberg , Hannes Reinecke Subject: Re: [dm-devel] [PATCH v10 1/8] block: Generalized bio pool freeing Message-ID: <20120918163156.GC17356@agk-dp.fab.redhat.com> Mail-Followup-To: Kent Overstreet , linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com, Jens Axboe , Lars Ellenberg , Hannes Reinecke References: <1346970902-10931-1-git-send-email-koverstreet@google.com> <1346970902-10931-2-git-send-email-koverstreet@google.com> <20120914182828.GK15728@agk-dp.fab.redhat.com> <20120917205139.GB14492@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120917205139.GB14492@google.com> Organization: Red Hat UK Ltd. Registered in England and Wales, number 03798903. Registered Office: 64 Baker Street, 4th floor, London, W1U 7DF. User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 17, 2012 at 01:51:39PM -0700, Kent Overstreet wrote: > That isn't a very good patch - it says it's clearing bi_end_io as a > precaution, but as a precaution to what? As a precaution against the endio function being called an extra time by mistake if a stray reference remains after the bio has been freed. Wipe this field when dm frees it. Defensive programming, basically, in response to a tricky bug he had to deal with. Alasdair