From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754059Ab2AZV41 (ORCPT ); Thu, 26 Jan 2012 16:56:27 -0500 Received: from mx1.redhat.com ([209.132.183.28]:13568 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751879Ab2AZV40 (ORCPT ); Thu, 26 Jan 2012 16:56:26 -0500 Date: Thu, 26 Jan 2012 16:56:08 -0500 From: Vivek Goyal To: Dirk Gouders Cc: Tejun Heo , Suresh Jayaraman , LKML , Jens Axboe Subject: Re: Slab corruption in floppy driver module Message-ID: <20120126215608.GD11297@redhat.com> References: <4F1EAFE9.5000306@suse.com> <20120124223153.GG17291@redhat.com> <20120126150420.GD1891@redhat.com> <20120126180532.GA4077@dhcp-172-17-108-109.mtv.corp.google.com> <20120126193735.GA11297@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 26, 2012 at 10:48:57PM +0100, Dirk Gouders wrote: > Vivek Goyal writes: > > > On Thu, Jan 26, 2012 at 10:05:32AM -0800, Tejun Heo wrote: > >> Hello, > >> > >> On Thu, Jan 26, 2012 at 10:04:20AM -0500, Vivek Goyal wrote: > >> > out_put_disk: > >> > while (dr--) { > >> > del_timer_sync(&motor_off_timer[dr]); > >> > - if (disks[dr]->queue) > >> > + if (disks[dr]->queue) { > >> > blk_cleanup_queue(disks[dr]->queue); > >> > + /* > >> > + * The request queue reference we took at device > >> > + * creation time has been put by above > >> > + * blk_cleanup_queue(). We have not called add_disk() > >> > + * yet and due to failure calling put_disk(). Put disk > >> > + * will try to put a reference to disk->queue which is > >> > + * taken in add_disk(). As we have not taken that > >> > + * extra reference, putting extra reference down > >> > + * will try to access already freed queue. Clear > >> > + * disk->queue before calling put_disk(). > >> > + */ > >> > + disks[dr]->queue = NULL; > >> > >> Yeah, this looks correct to me. It might be better to tone down the > >> comment a bit tho. Wouldn't it be sufficient to say put_disk() isn't > >> paired with add_disk() and will put one extra time? > > > > Sure. Toned down the comment as suggested. Here is the new patch. > > > > floppy: Cleanup disk->queue before caling put_disk() if add_disk() was never called > > > > add_disk() takes gendisk reference on request queue. If driver failed during > > initialization and never called add_disk() then that extra reference is not > > taken. That reference is put in put_disk(). floppy driver allocates the > > disk, allocates queue, sets disk->queue and then relizes that floppy > > controller is not present. It tries to tear down everything and tries to > > put a reference down in put_disk() which was never taken. > > > > In such error cases cleanup disk->queue before calling put_disk() so that > > we never try to put down a reference which was never taken in first place. > > > > Reported-by: Suresh Jayaraman > > Tested-by: Dirk Gouders > > Signed-off-by: Vivek Goyal > > --- > > drivers/block/floppy.c | 8 +++++++- > > 1 file changed, 7 insertions(+), 1 deletion(-) > > > > Index: linux-2.6/drivers/block/floppy.c > > =================================================================== > > --- linux-2.6.orig/drivers/block/floppy.c 2012-01-15 09:49:14.000000000 -0500 > > +++ linux-2.6/drivers/block/floppy.c 2012-01-26 14:35:14.662374464 -0500 > > @@ -4368,8 +4368,14 @@ out_unreg_blkdev: > > out_put_disk: > > while (dr--) { > > del_timer_sync(&motor_off_timer[dr]); > > - if (disks[dr]->queue) > > + if (disks[dr]->queue) { > > blk_cleanup_queue(disks[dr]->queue); > > + /* > > + * put_disk() is not paired with add_disk() and > > + * will put queue reference one extra time. fix it. > > + */ > > + disks[dr]->queue = NULL; > > + } > > put_disk(disks[dr]); > > } > > return err; > > > Probably a rare and uncommon one but it seems that the reloading case on > a machine that has a floppy controller is a different problem. To be > sure I tested the patch on a machine that has a floppy controller and > when unloading and reloading the floppy module the log messages that I > attached to a mail earlier in this thread are still generated. Ok. Thanks for the update. I had assumed that it solved both the issues. So, module load/unload seems to be a different problem. We should still take this patch as it solves atleast the case of floppy controller not being present. Jens, do you want me to post the patch in a separate mail thread? Thanks Vivek