linux-kernel - Re: 2.6.31-rc5 regression: Oops when USB Serial disconnected while in use

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Message-ID: <Pine.LNX.4.44L0.0908210958100.2912-100000@iolanthe.rowland.org>
Date:	Fri, 21 Aug 2009 10:02:51 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	Bruno Prémont <bonbons@...ux-vserver.org>,
	Greg KH <greg@...ah.com>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: 2.6.31-rc5 regression: Oops when USB Serial disconnected while
 in use

On Thu, 20 Aug 2009, Alan Cox wrote:

> So the tty layer always went that way so that the awkward cases around an
> opening failing with a hangup just go away. For the normal drivers which
> basically do
> 
> open:
> 	tty layer open work
> 		open hardware and set ASYNCB_INITIALIZED
> 	block for carrier
> 
> close:
> 	if (!hung_up) {
> 		if initialized
> 			shutdown()
> 	}
> 
> the USB layer works really hard to be completely different (in part
> because the old code simply didn't implement open semantics properly or
> hangup correctly - hence things like mgetty fail on them).
> 
> The later patches I was working on were trying to get USB serial to the
> point where the model was that drv->open/drv->close were the hardware
> init/shutdown and did indeed get called in nice matching open/close pairs
> and not re-entered or called unserialized.

That is indeed the best approach.  How much is still needed to make it 
work?

> Nice spot on the ASYNC v ASYNCB bug Alan btw

Hah!  Crashing with a big oops was a pretty strong hint that something
was wrong.  The tricky part was grovelling through the disassembly 
listing and figuring out why the offsets were so huge.  :-)

Alan Stern

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