linux-kernel - Re: [PATCH 2/2] [RFC] Remove BKL from fs/locks.c

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Message-Id: <201004152236.19732.arnd@arndb.de>
Date:	Thu, 15 Apr 2010 22:36:19 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	Trond Myklebust <trond.myklebust@....uio.no>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Christoph Hellwig <hch@....de>,
	Miklos Szeredi <mszeredi@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, John Kacur <jkacur@...hat.com>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 2/2] [RFC] Remove BKL from fs/locks.c

On Wednesday 14 April 2010 23:04:03 J. Bruce Fields wrote:
> The lockd thread is entirely under the BKL--it takes it at the top of
> fs/lockd/svc.c:lockd(), and drops it at the bottom.  It's possible
> there may be code that lockd runs that assumes mutual exclusion with
> code in locks.c, but I don't know.

That one seems interesting as the lockd thread calls lots of sleeping
functions as well as file lock code that takes the BKL again, both
of which of course is not allowed when converting to a spinlock.

I just attempted to blindly convert lockd to taking lock_flocks()
in place of the BKL and releasing it where necessary, but quickly gave
up because this seems rather pointless. It basically never does
anything interesting between places where it would need to drop the
lock.

	Arnd
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