linux-kernel - Re: [PATCH] usb: f_mass_storage: test whether thread is running before starting another

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Date:	Wed, 6 Apr 2016 11:05:52 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Michal Nazarewicz <mina86@...a86.com>
cc:	Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
	Tony Lindgren <tony@...mide.com>,
	<linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>,
	Felipe Balbi <felipe.balbi@...ux.intel.com>,
	Bin Liu <b-liu@...com>, <pali.rohar@...il.com>
Subject: Re: [PATCH] usb: f_mass_storage: test whether thread is running
 before starting another

On Wed, 6 Apr 2016, Michal Nazarewicz wrote:

> On Tue, Apr 05 2016, Alan Stern wrote:
> > Suppose one usb_function is carrying out an I/O operation while
> > another one in the same config gets a Set-Interface request from the
> > host.
> 
> That cannot happen.  A single instance of mass_storage cannot¹ be added
> twice to the same configuration.
> 
> ¹ To be more precise, not via configfs.  A legacy gadget could do that,
>   but that would be a bug in that legacy driver, not f_mass_storage.
>   Moreover, no current legacy gadgets do that though so IMO this is an
>   academic discussion.

Okay.  Then I suggest adding this explanation to the patch description.

BTW, is configfs capable of adding a single instance twice in different 
configs?  Or is that again something only legacy gadgets can do?

Alan Stern