linux-kernel - possible locking bug in tty

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Message-Id: <201005022247.33857.arnd@arndb.de>
Date:	Sun, 2 May 2010 22:47:33 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Alan Cox <alan@...ux.intel.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	"Greg Kroah-Hartman" <gregkh@...e.de>
Subject: possible locking bug in tty_open

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().

	Arnd
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