linux-kernel - Re: BUG: NULL pointer deref in tty port / uart

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Message-ID: <20110518153636.5cdcdd78@lxorguk.ukuu.org.uk>
Date:	Wed, 18 May 2011 15:36:36 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Alan Cox <alan@...ux.intel.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Kay Sievers <kay.sievers@...y.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Arnd Bergmann <arnd@...db.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: BUG: NULL pointer deref in tty port / uart

> have the same issue.. looks like we should not NULL the port->tty
> if there's blocked open, but not sure what's exactly the logic
> behind "port's block_open and count" ..

A pending open is not a user of the tty as far as the rest of the stack
is concerned. I also don't see why clearing port->tty is causing this
crash because nothing on that path should ever be going via port->tty and
it isn't safe to do so.

> attached patch fixes it for me

But still breaks on hangup where we can't do that.

Where is port->tty getting misused to cause the crash, that is the bit
I'm missing somewhere.
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