From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bart Van Assche Subject: Re: [PATCH v11 6/9] Make scsi_remove_host() wait until error handling finished Date: Tue, 25 Jun 2013 17:31:29 +0200 Message-ID: <51C9B7D1.9040702@acm.org> References: <51B86E26.6030108@acm.org> <51B86FC1.6000103@acm.org> <1372101557.2013.76.camel@dabdike.int.hansenpartnership.com> <51C8A668.3060700@cs.wisc.edu> <1372112866.2013.104.camel@dabdike.int.hansenpartnership.com> <51C95C79.2080804@acm.org> <1372167923.2806.13.camel@dabdike> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from georges.telenet-ops.be ([195.130.137.68]:40191 "EHLO georges.telenet-ops.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752502Ab3FYPbc (ORCPT ); Tue, 25 Jun 2013 11:31:32 -0400 In-Reply-To: <1372167923.2806.13.camel@dabdike> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: Mike Christie , linux-scsi , Joe Lawrence , Tejun Heo , Chanho Min , David Milburn , Hannes Reinecke On 06/25/13 15:45, James Bottomley wrote: > On Tue, 2013-06-25 at 11:01 +0200, Bart Van Assche wrote: >> There is a difference though between moving the EH kthread_stop() call >> and the patch at the start of this thread: moving the EH kthread_stop() >> call does not prevent that an ioctl like SG_SCSI_RESET triggers an eh_* >> callback after scsi_remove_host() has finished. However, the >> scsi_begin_eh() / scsi_end_eh() functions do prevent that an ioctl can >> cause an eh_* callback to be invoked after scsi_remove_device() finished. > > OK, but this doesn't tell me what you're trying to achieve. > > An eh function is allowable as long as the host hadn't had the release > callback executed. That means you must have to have a reference to the > device/host to execute the eh function, which is currently guaranteed > for all invocations. That raises a new question: how is an LLD expected to clean up resources without triggering a race condition ? What you wrote means that it's not safe for an LLD to start cleaning up the resources needed by the eh_* callbacks immediately after scsi_remove_device() returns since it it not guaranteed that at that time all references to the device have already been dropped. Bart.