Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755736Ab2HPHwo (ORCPT ); Thu, 16 Aug 2012 03:52:44 -0400 Received: from relay03ant.iops.be ([212.53.5.218]:59881 "EHLO relay03ant.iops.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751606Ab2HPHwm (ORCPT ); Thu, 16 Aug 2012 03:52:42 -0400 Message-ID: <502CA6C3.4040903@acm.org> Date: Thu, 16 Aug 2012 07:52:35 +0000 From: Bart Van Assche User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120713 Thunderbird/14.0 MIME-Version: 1.0 To: Chanho Min CC: James Bottomley , Mike Christie , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, Jens Axboe , Tejun Heo Subject: Re: [PATCH RESEND] remove the queue unlock in scsi_requset_fn References: <1344946071.3117.26.camel@dabdike.int.hansenpartnership.com> In-Reply-To: X-Enigmail-Version: 1.5a1pre Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1230 Lines: 25 On 08/16/12 01:35, Chanho Min wrote: >> functions will occur in line. I also don't see why the sdev reference >> couldn't drop to zero here. > scsi_request_fn is called under the lock of request_queue->queue_lock. > If we drop the sdev reference to zero here, > scsi_device_dev_release_usercontext is > invoked and make request_queue to NULL. When caller of scsi_request_fn try to > unlock request_queue->queue_lock, the oops is occurred. Whether or not your patch is applied, if the put_device() call in scsi_request_fn() decreases the sdev reference count to zero, the scsi_request_fn() caller will still try to unlock the queue lock after scsi_request_fn() finished and hence will trigger a use-after-free. I'm afraid the only real solution is to modify the SCSI and/or block layers such that scsi_remove_device() can't finish while scsi_request_fn() is in progress. And once that is guaranteed the get_device() / put_device() pair can be left out from scsi_request_fn(). Bart. -- 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/