From: Oliver Neukum <oliver@neukum.org>
To: Alan Stern <stern@rowland.harvard.edu>
Subject: Re: [PATCH 4/5] usb_serial: Kill port mutex
Date: Thu, 8 Oct 2009 13:37:09 +0200
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Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, Greg KH <greg@kroah.com>,
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Am Mittwoch, 7. Oktober 2009 19:23:59 schrieb Alan Stern:
> > We can take the port->mutex lock in the throttle/unthrottle methods as
> > far as I can see - there are no obvious problem cases. We do call
> > ->throttle and ->unthrottle from the ldisc open but this occurs outside
> > of any call to the tty driver open/close method so I don't see any
> > deadlock.
> >
> > It adds an ordering of termios lock before port mutex when taking both
> > but that's not a problem and really implicit in the structure of the code
> > anyway.
>
> Does this imply that unthrottle should try to autoresume? ?There does
> appear to be a potential race between unthrottle and autosuspend.

The race exists. But I don't think unthrottle should autoresume.
It would be better to just set a flag and defer this to resume.
If the device supports remote wakeup there'll be no need to autoresume,
if not, throttle/unthrottle are too rare to justify the complexity.

	Regards
		Oliver

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