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

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Date:	Thu, 8 Oct 2009 15:43:01 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, 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

Am Mittwoch, 7. Oktober 2009 23:34:12 schrieb Alan Stern:
> I'm losing track of the original point of this thread.  IIRC, the
> problem is how the resume method should know whether or not to submit
> the receive URB(s).  It can't afford to acquire the port mutex because
> it might be called by open or close, at which time the mutex is already
> held.
>
> Other schemes could work, but to me it seems simplest to rely on a flag
> protected by a spinlock.  The flag would mean "URBs are supposed to be
> queued unless we are suspended".  It would be set by open and
> unthrottle, and cleared by close and throttle.

1. Why a spinlock?
2. Can we get by with only one flag?

	Regards
		Oliver


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