linux-kernel - Re: [RFC][PATCH] reiserfs vs BKL

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Date:	Sat, 21 Apr 2007 12:14:41 -0400
From:	Jeff Mahoney <jeffm@...e.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	reiserfs-list@...esys.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Chris Mason <chris.mason@...cle.com>,
	Nikita Danilov <nikita@...sterfs.com>
Subject: Re: [RFC][PATCH] reiserfs vs BKL

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Peter Zijlstra wrote:
> Replace all the lock_kernel() instances with reiserfs_write_lock(sb),
> and make that use an actual per super-block mutex instead of
> lock_kernel().
> 
> This should make reiserfs safe from PREEMPT_BKL=n, since it seems to
> rely on being able to schedule. Also, it removes the dependency on the
> BKL, and thereby is not prone to cause prio inversion with remaining BKL
> users (notably tty).
> 
> Compile tested only, since I didn't dare boot it.

NACK.

Believe me, I would *love* to nuke the BKL from reiserfs, but a search
and replace of this nature is just wrong. reiserfs_write_lock() using
the BKL isn't an accident - it depends on its nesting properties. If you
did try to boot this kernel, you'd deadlock pretty quickly.

This one has been on my TODO list for a long time. Interestingly, I've
been doing reiserfs xattr development recently using 2.6.21-rc7-git2,
and I'm not seeing any of these messages.

# CONFIG_PREEMPT_NONE is not set
CONFIG_PREEMPT_VOLUNTARY=y
# CONFIG_PREEMPT is not set
# CONFIG_PREEMPT_BKL is not set

- -Jeff

- --
Jeff Mahoney
SUSE Labs
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