From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH 00/40] Staging: hv: Driver cleanup Date: Fri, 1 Jul 2011 04:21:36 -0400 Message-ID: <20110701082136.GE28322@infradead.org> References: <1309358301-8488-1-git-send-email-kys@microsoft.com> <20110630193346.GA22707@infradead.org> <6E21E5352C11B742B20C142EB499E0480816C36D@TK5EX14MBXC126.redmond.corp.microsoft.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <6E21E5352C11B742B20C142EB499E0480816C36D@TK5EX14MBXC126.redmond.corp.microsoft.com> Sender: linux-kernel-owner@vger.kernel.org To: KY Srinivasan Cc: Christoph Hellwig , "gregkh@suse.de" , "linux-kernel@vger.kernel.org" , "devel@linuxdriverproject.org" , "virtualization@lists.osdl.org" List-Id: virtualization@lists.linuxfoundation.org On Thu, Jun 30, 2011 at 11:28:27PM +0000, KY Srinivasan wrote: > > On Wed, Jun 29, 2011 at 07:38:21AM -0700, K. Y. Srinivasan wrote: > > > Further cleanup of the hv drivers: > > > > > > 1) Cleanup the reference counting mess for both stor and net devices. > > > > I really don't understand the need for reference counting on the storage > > side, especially now that you only have a SCSI driver. The SCSI > > midlayer does proper counting on it's objects (Scsi_Host, scsi_device, > > scsi_cmnd), so you'll get that for free given that SCSI drivers just > > piggyback on the midlayer lifetime rules. > > The reference counting allows us to properly deal with messages coming back from the host > to the guest with a racing remove of the device. I am told these messages could potentially be > not a response to a message sent from the guest. To deal with that the scsi subsystem has a two stage teardown for the SCSI host. First you call scsi_remove_host, at which point no new I/O to it can be started. After that you can wait for all outstanding messages, and finally you do a scsi_host_put to drop the long-term reference to it, and eventually free it.