linux-kernel - Re: [PATCH 11/11] usb: core: fix a race with usb_queue_reset

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Message-ID: <20150121135512.GA9889@hposo>
Date:	Wed, 21 Jan 2015 14:55:12 +0100
From:	Olivier Sobrie <olivier@...rie.be>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Jan Dumon <j.dumon@...ion.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH 11/11] usb: core: fix a race with usb_queue_reset_device()

Hello Alan,

On Tue, Jan 20, 2015 at 10:26:30AM -0500, Alan Stern wrote:
> On Tue, 20 Jan 2015, Olivier Sobrie wrote:
> 
> > When usb_queue_reset() is called it schedules a work in view of
> > resetting the usb interface. When the reset work is running, it
> > can be scheduled again (e.g. by the usb disconnect method of
> > the driver).
> > 
> > Consider that the reset work is queued again while the reset work
> > is running and that this work leads to a forced unbinding of the
> > usb interface (e.g. because a driver is bound to the interface
> > and has no pre/post_reset methods - see usb_reset_device()).
> > In such condition, usb_unbind_interface() gets called and this
> > function calls usb_cancel_queued_reset() which does nothing
> > because the flag "reset_running" is set to 1. The second reset
> > work that has been scheduled is therefore not cancelled.
> > Later, the usb_reset_device() tries to rebind the interface.
> > If it fails, then the usb interface context which contain the
> > reset work struct is freed and it most likely crash when the
> > second reset work tries to be run.
> 
> There was an earlier patch posted for testing (no results yet)  
> affecting this same region of code:
> 
> 	http://marc.info/?l=linux-usb&m=142064533924019&w=2
> 
> It should fix the problem described here, because (among other things) 
> it adds usb_get/put_intf calls to the delayed-reset routines.

I tested your patch. It also fixes the problem I observed.
You can drop mine.

For your info:

My test consists in powering down a usb hso modem while one of its
serial port is opened. It leads to two URB failures, each urb callback
queues a reset.
Without your fix (or without the one I sent), a crash happens after
less than ~20 power up/down sequences. With your fix, after more than
1000 power up/down I don't see any crash.

Thanks,

-- 
Olivier
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