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

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Message-ID: <Pine.LNX.4.44L0.0908222236100.11562-100000@netrider.rowland.org>
Date:	Sat, 22 Aug 2009 22:51:27 -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

Alan:

There's a problem with the tty->ops->shutdown method.  It needs to
release the last port reference owned by the current tty.  But when was
that reference originally acquired?  Evidently during the first time
serial_open() was called for the current tty.

The problem is that serial_open() has no way to know if a particular 
invocation is the first one for this tty!  The ASYNCB_INITIALIZED flag 
doesn't help, because it might not get set during the first call (i.e., 
if an error occurs).

To do this right, we need a flag in the tty_struct or the tty_port
which serial_open() can set when acquiring that first reference and
shutdown method can clear.  Should I add such a flag?

Alan Stern

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