From: Jonathan Corbet <corbet@lwn.net>
To: Jonathan Corbet <corbet@lwn.net>
Cc: John Kacur <jkacur@redhat.com>,
Alan Cox <alan@lxorguk.ukuu.org.uk>,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Frederic Weisbecker <fweisbec@gmail.com>,
Christoph Hellwig <hch@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
Vincent^M^J Sanders <vince@simtec.co.uk>,
Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH] sound_core.c: Remove BKL from soundcore_open
Date: Sun, 11 Oct 2009 11:15:43 -0600 [thread overview]
Message-ID: <20091011111543.1cbb9a0e@tpl.lwn.net> (raw)
In-Reply-To: <20091011092015.37a69847@bike.lwn.net>
On Sun, 11 Oct 2009 09:20:15 -0600
Jonathan Corbet <corbet@lwn.net> wrote:
> Changing the
> BKL to a mutex is a real semantic change which requires a real survey
> of the code affected.
One other aspect of this I forgot to mention...it's actually possible
(if unlikely) that one of those lower-level open routines depends on
the BKL's release-on-sleep semantics. Swapping in a mutex would change
that behavior, possibly resulting in deadlocks.
I think it was Alan who once pointed out that the BKL is badly
misnamed. It isn't really a lock, it's a modified execution
environment designed to let naive kernel code think it's still running
in a uniprocessor, no-preemption situation. Replacing the BKL with a
different lock changes that environment, so one has to be *really*
careful about looking for any assumptions which may remain in the code.
That's why BKL-hunting is harder than it looks - and why the BKL has
hung around for all these years.
jon
next prev parent reply other threads:[~2009-10-11 17:16 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-10 23:24 [PATCH] sound_core.c: Remove BKL from soundcore_open John Kacur
2009-10-10 23:42 ` Alan Cox
2009-10-11 0:25 ` John Kacur
2009-10-11 11:33 ` Frederic Weisbecker
2009-10-11 12:41 ` John Kacur
2009-10-11 14:12 ` Oliver Neukum
2009-10-11 20:40 ` Frederic Weisbecker
2009-10-11 21:25 ` John Kacur
2009-10-12 6:05 ` Takashi Iwai
2009-10-12 8:37 ` John Kacur
2009-10-12 10:17 ` Takashi Iwai
2009-10-12 10:42 ` John Kacur
2009-10-11 15:20 ` Jonathan Corbet
2009-10-11 17:15 ` Jonathan Corbet [this message]
2009-10-11 17:37 ` Arjan van de Ven
2009-10-11 19:17 ` Alan Cox
2009-10-11 19:26 ` Arjan van de Ven
2009-10-11 20:51 ` Alan Cox
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