From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Christie Subject: Re: Serious regression caused by fix for [BUG 1/3] bsg queue oops with iscsi logout Date: Wed, 26 Mar 2008 21:18:02 -0500 Message-ID: <47EB03DA.805@cs.wisc.edu> References: <1206201960.4393.8.camel@localhost.localdomain> <20080326232226X.tomof@acm.org> <1206542186.3019.5.camel@localhost.localdomain> <20080326235900H.tomof@acm.org> <47EAFDB0.4090503@cs.wisc.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from sabe.cs.wisc.edu ([128.105.6.20]:35298 "EHLO sabe.cs.wisc.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754068AbYC0CSa (ORCPT ); Wed, 26 Mar 2008 22:18:30 -0400 In-Reply-To: <47EAFDB0.4090503@cs.wisc.edu> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: FUJITA Tomonori Cc: James.Bottomley@HansenPartnership.com, pw@osc.edu, fujita.tomonori@lab.ntt.co.jp, linux-scsi@vger.kernel.org, erezz@voltaire.com, Jens.Axboe@oracle.com Mike Christie wrote: > FUJITA Tomonori wrote: >> On Wed, 26 Mar 2008 07:36:26 -0700 >> James Bottomley wrote: >> >>> On Wed, 2008-03-26 at 23:22 +0900, FUJITA Tomonori wrote: >>>> On Sat, 22 Mar 2008 11:06:00 -0500 >>>> James Bottomley wrote: >>>> >>>>> On Tue, 2008-03-11 at 00:36 -0500, Mike Christie wrote: >>>>>> Mike Christie wrote: >>>>>>> Pete Wyckoff wrote: >>>>>>>> I think this used not to happen; not sure. But I changed two >>>>>>>> things >>>>>>> This most likely did not happen before 2.6.25-rc* or it broke in >>>>>>> slightly different ways, because iscsi used to try and do >>>>>>> >>>>>>> echo 1 > /sys/block/sdX/device/delete >>>>>>> >>>>>>> from userspace instead of calling scsi_remove_target from the >>>>>>> kernel. >>>>>>> >>>>>>> As you know around 2.6.21, the behavior of doing the echo to the >>>>>>> delete file changed due to a driver model and scsi change and >>>>>>> that broke the iscsi tools. The iscsi tools userspace removal was >>>>>>> sort of hack in the first place and was racey, so we switched to >>>>>>> removing devices/target like the FC class. >>>>>>> >>>>>>> >>>>>>>> lately. 2.6.25-rc1 to -rc4 and fedora 8 iscsi-initiator-utils >>>>>>>> (865) to >>>>>>>> fedora devel (868). Bidi and varlen patches always too. >>>>>>>> >>>>>>>> I'll follow with some more variations on this theme. Looks like >>>>>>>> bsg >>>>>>>> needs to protect more carefully against the device going away. Any >>>>>>>> ideas how best to do this? What was the approach in sg? >>>>>>>> >>>>>>> I think sg is broken in similar ways. The iser guys have some >>>>>>> tests cases that have broken sg while IO is outstanding. I am >>>>>>> ccing Erez. >>>>>> Actually one of the problems looks a little different than some of >>>>>> the problems hit with sg and are caused because we remove the bsg >>>>>> device too soon. I think we want to wait until all the references >>>>>> from the commands/requests are released. The attached patch >>>>>> (untested) moves the bsg unreg call to the scsi device release fn. >>>>> Well, this fix is now upstream. However, it's causing all our >>>>> scsi_devices never to get released, which is a serious regression. >>>>> We're also doing spurious bsg_unregister_queue() for things that never >>>>> actually registered one (all scan devices that return DID_NO_CONNECT), >>>>> but bsg doesn't seem to be complaining about this. >>>>> >>>>> The essence of the problem is that bsg_register_queue() takes a ref to >>>>> the sdev_gendev, so you can't move bsg_unregister_queue() into the >>>>> release function because nothing ever puts bsg's device ref and so >>>>> release is never called. >>>>> >>>>> Options for fixing this before 2.6.25 are >>>>> >>>>> 1. revert the patch >>>>> 2. Do an additional put for the bsg reference in >>>>> __scsi_remove_device (patch below). It's nasty but it >>>>> preserves >>>>> the semantics and does what you want >>>> After some investigation, this patch doesn't fix the bug that Pete >>>> reported (I'll send a new patch shortly). >>>> >>>> Can you revert the commit 4b6f5b3a993cbe34b4280f252bccc76967c185c8 >>>> instead of merging this? >>> Sure ... I didn't like the hack either. As long as iSCSI is fine with >>> the reversion it's the quickest way to fix the problem. >> >> How about this? With the commit reversion, I confirmed that this patch >> fixes the first bug that Pete reported: >> >> http://marc.info/?l=linux-scsi&m=120508166505141&w=2 >> >> I suspect that this could fix the rest too. >> >> = >> From: FUJITA Tomonori >> Subject: [PATCH] bsg: takes a ref to struct device in fops->open >> >> bsg_register_queue() takes a ref to struct device that a caller >> passes. For example, it takes a ref to the sdev_gendev with scsi >> devices. However, bsg doesn't takes a ref to it in fops->open. So >> while an application opens a bsg device, the scsi device that the bsg >> device holds can go away (bsg also takes a ref to a queue, but it >> doesn't prevent the device from going away). >> >> With this, bsg takes a ref to struct device in fops->open and frees it >> in fops->release. >> >> Note that bsg doesn't need to takes a ref to a queue for SCSI devices >> at least. I think that it would be better to remove the code but I let >> it alone for now. >> > > Why does bsg_add_device do kobject_get instead of blk_get_queue? > > It seems like if we added a blk_qet_queue when we opened the device and > a blk_put_queue when bsg_release is called we could remove the > get/put_device calls. I am not sure if that is cleaner or not. I was > just thinking that bsg goes from bsg->request_queue->scsi_device so > maybe it should not worry about the device. Doh, I guess we sort of do this today. It looks like the blk_execute functions are bypassing the QUEUE_FLAG_DEAD checks, so scsi_device_dev_release_usercontext could have called scsi_free_queue, but if bsg calls blk_execute at the same time then it could stick a request into the queue and end up calling the scsi_request_fn (maybe this is what happens in #2 and when scsi_request_fn calls get_device we get that weird error since the refcount on the device is zero).