linux-kernel - Re: [PATCH 4/5] usb_serial: Kill port mutex

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Date:	Wed, 7 Oct 2009 14:52:21 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	Oliver Neukum <oliver@...kum.org>, Greg KH <greg@...ah.com>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>
Subject: Re: [PATCH 4/5] usb_serial: Kill port mutex

On Wed, 7 Oct 2009, Alan Cox wrote:

> > > It would probably be cleaner if they could lock against each other
> > 
> > What you mean isn't clear.  After all, open sometimes has to call
> > resume.  So how could resume lock against open?
> 
> Probably it needs a counting lock as the code is currently structured -
> which is a bit ugly. What paths do we end up going through the device
> open method into resume in the same thread ?

Currently there are no such paths.  I keep forgetting that the resume
is done in serial_install() rather than serial_open().  Eventually the
tty_port reorganization will probably force the resume to move into the
activate method.

However in the option and sierra drivers there is a perverse path from
close to resume: Both their close methods call
usb_autopm_get_interface().  This could be removed without much
trouble; perhaps we should do so.

Alan Stern

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