linux-kernel - Re: possible locking bug in tty

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Message-ID: <20100504104305.29e7ada7@linux.intel.com>
Date:	Tue, 4 May 2010 10:43:05 +0100
From:	Alan Cox <alan@...ux.intel.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	"Greg Kroah-Hartman" <gregkh@...e.de>
Subject: Re: possible locking bug in tty_open

On Sun, 2 May 2010 22:47:33 +0200
Arnd Bergmann <arnd@...db.de> wrote:

> While playing some more with my TTY BKL patches, I stumbled over
> what looks like a bug in tty_open, introduced in e8c6210 
> "tty: push the BKL down into the handlers a bit":
> 
> After the "retry_open:" label, we first get the tty_mutex
> and then the BKL. However a the end of tty_open, we jump
> back to retry_open with the BKL still held. If we run into
> this case, the tty_open function will be left with the BKL
> still held.
> 
> It may be impossible to actually trigger this bug, because
> the path is only taken if a tty driver open function returns
> -ERESTARTSYS without setting signal_pending().

It looks pretty much impossible to trigger but it's definitely a bug.
I'll send Greg a patch
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