linux-kernel - Re: [RFC 22/22] tcm_loop: Add multi-fabric Linux/SCSI LLD fabric module

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Message-Id: <1283752861.556.200.camel@haakon2.linux-iscsi.org>
Date:	Sun, 05 Sep 2010 23:01:01 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Greg KH <gregkh@...e.de>, linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Mike Christie <michaelc@...wisc.edu>,
	Christoph Hellwig <hch@....de>, Hannes Reinecke <hare@...e.de>,
	James Bottomley <James.Bottomley@...e.de>,
	Jens Axboe <axboe@...nel.dk>,
	Boaz Harrosh <bharrosh@...asas.com>
Subject: Re: [RFC 22/22] tcm_loop: Add multi-fabric Linux/SCSI LLD fabric
	module

On Sun, 2010-09-05 at 22:38 -0700, Dmitry Torokhov wrote:
> On Sun, Sep 05, 2010 at 10:21:20PM -0700, Nicholas A. Bellinger wrote:
> > On Sun, 2010-09-05 at 22:17 -0700, Greg KH wrote:
> > > On Sun, Sep 05, 2010 at 10:08:16PM -0700, Dmitry Torokhov wrote:
> > > > On Sun, Sep 05, 2010 at 02:51:19PM -0700, Nicholas A. Bellinger wrote:
> > > > > On Sun, 2010-09-05 at 13:30 -0700, Dmitry Torokhov wrote:
> > > > > > On Mon, Aug 30, 2010 at 02:23:23AM -0700, Nicholas A. Bellinger wrote:
> > > > > > > +
> > > > > > > +static void tcm_loop_primary_release(struct device *dev)
> > > > > > > +{
> > > > > > > +	return;
> > > > > > > +}
> > > > > > > +
> > > > > > > +static struct device tcm_loop_primary = {
> > > > > > > +	.init_name		= "tcm_loop_0",
> > > > > > > +	.release		= tcm_loop_primary_release,
> > > > > > > +};
> > > > > > > +
> > > > > > 
> > > > > > No, you can not have statically allocated devices and dummy release
> > > > > > functions.
> > > > > > 
> > > > > 
> > > > > Last time I checked this is still what mainline
> > > > > drivers/scsi/scsi_debug.c is doing for struct device pseudo_primary:
> > > > > 
> > > > > static void pseudo_0_release(struct device *dev)
> > > > > {
> > > > >         if (SCSI_DEBUG_OPT_NOISE & scsi_debug_opts)
> > > > >                 printk(KERN_INFO "scsi_debug: pseudo_0_release() called\n");
> > > > > }
> > > > > 
> > > > > static struct device pseudo_primary = {
> > > > >         .init_name      = "pseudo_0",
> > > > >         .release        = pseudo_0_release,
> > > > > };
> > > > > 
> > > > > so for these type of things in TCM_Loop I tend to follow what scsi_debug does,
> > > > >  so I don't exactly see a issue here atm.  Anybody else have comments..?
> > > > 
> > > > The kobject embedded in the device structure is refcounted and it's
> > > > lifetime may be different from lifetime of your module. If somebody
> > > > happen to hold reference to the driver while your module is being
> > > > unloaded bad things will happen.
> > > > 
> > > > I am sure Greg has something on this topic ready for cut-and-paste.
> > > 
> > > Documentation/kobject.txt :)
> > 
> > I still don't get it..?  Does this mean that scsi_debug and TCM_Loop are
> > currently broken wrt to this item or not..?
> > 
> 
> Yes they are broken.

Hi Dmitry and Greg,

Would you mind giving a bit more specific idea as to what a patch to fix
this issue would involve for an emulated struct device usage..?  I would
be happy to generate patches for scsi_debug and TCM_loop to resolve this
issue, but I need a bit more information what I should be looking at.

Thanks,

--nab


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