linux-kernel - Re: [PATCH 6/6] procfs: Kill the bkl in ioctl

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Message-Id: <201004011107.13774.arnd@arndb.de>
Date:	Thu, 1 Apr 2010 11:07:13 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	John Kacur <jkacur@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Al Viro <viro@...iv.linux.org.uk>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 6/6] procfs: Kill the bkl in ioctl

On Wednesday 31 March 2010, Alan Cox wrote:
> > The recursive users that I've removed in my series are the block, tty,
> > input and sound subsystems, as well as the init code.
> 
> There are some very subtle recursive cases in the tty code - hangup
> triggered close and consoles being an absolute gem I've just had to debug
> in my lock removal bits so far...

Yes, I've seen some of them. What I meant above is that with
CONFIG_TTY_MUTEX=y, the TTY code no longer uses the BKL in a
nested way, and quite likely no either code does either.

The TTY code with my patch now has tty_lock() for all cases that
I concluded are never nested in another tty_lock, and tty_lock_nested()
for those I did not understand or that I know they are nested (the
latter type usually comes with a comment). The only difference
between the two is a WARN_ON(tty_locked()) in tty_lock, so we can
see where the analysis was wrong.

	Arnd
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