From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753742Ab2AZThz (ORCPT ); Thu, 26 Jan 2012 14:37:55 -0500 Received: from mx1.redhat.com ([209.132.183.28]:35794 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751854Ab2AZThy (ORCPT ); Thu, 26 Jan 2012 14:37:54 -0500 Date: Thu, 26 Jan 2012 14:37:35 -0500 From: Vivek Goyal To: Tejun Heo Cc: Suresh Jayaraman , LKML , Jens Axboe , Dirk Gouders Subject: Re: Slab corruption in floppy driver module Message-ID: <20120126193735.GA11297@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120126180532.GA4077@dhcp-172-17-108-109.mtv.corp.google.com> 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 10:05:32AM -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;