linux-kernel - Re: [PATCH] fix usb skeleton driver

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Message-ID: <CACVXFVOurE3oaA5GLPkDQLeHP4sT4i0B0J_RPG_u2CL-VSFP7Q@mail.gmail.com>
Date:	Thu, 7 Jun 2012 09:05:30 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Stefani Seibold <stefani@...bold.net>
Cc:	linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
	oneukum@...e.de, alan@...rguk.ukuu.org.uk,
	linux-usb@...r.kernel.org
Subject: Re: [PATCH] fix usb skeleton driver

On Wed, Jun 6, 2012 at 11:05 PM, Stefani Seibold <stefani@...bold.net> wrote:
>>
>> This one is not needed since we have minor_rwsem(drivers/usb/core/file.c)
>> to avoid the race.
>>
>
> The mutex is not for the minor handling, it is for the disconnect(). As

usb_deregister_dev is called by disconnect, and usb_deregister_dev
will acquire minor_rwsem, so there is no race between open and disconnect.
When skel_open is being called, the minor_rwsem has been held already,
so disconnect() will staying on acquiring minor_rwsem.

So sync_mutex is not necessary at all.

> mentioned in the previous posting, there is a race betwenn open() and
> connect().
>
> Oliver told me that a interface pointer can be already used by an other
> driver when the disconnect() was called.

If you mean dev->interface, that is protected by io_mutex already.


Thanks,
-- 
Ming Lei
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