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

From: Arnd Bergmann
Date: Thu Apr 01 2010 - 05:07:49 EST

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.

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