linux-kernel - Re: [PATCH RFC] BKL not necessary in cpuid

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Date:	Fri, 9 Oct 2009 17:55:21 -0400 (EDT)
From:	John Kacur <jkacur@...hat.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	tglx@...utronix.de, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	Clark Williams <williams@...hat.com>
Subject: Re: [PATCH RFC] BKL not necessary in cpuid_open

----- "Arnd Bergmann" <arnd@...db.de> wrote:

> On Wednesday 07 October 2009, John Kacur wrote:
> > 
> > I've been staring at the BKL lock in cpuid_open, and I can't see
> what it 
> > is protecting. However, I may have missed something - even something
> 
> > obvious, so comments are welcome.
> > 
> 
> Hi John,
> 
> In general, the lock_kernel() calls in any chardev open() file
> operation
> are the result of the BKL pushdown by Jon Corbet and others, which has
> happened
> some time last year[1]. I'd assume that the vast majority is not
> needed
> at all, so these are an easy target for removal.
> 
> 	Arnd
> 
> [1] http://lkml.indiana.edu/hypermail/linux/kernel/0805.2/0257.html

yup - I'm aware of all the hard work that many people put in before I ever looked at this.
Thomas asked the -rt folks to have a look at removing the bkl look during the rt-mini summit
in Dresden. I was looking for low hanging fruit to get started. The confusion was over what
was already implemented in tip/rt/bkl. I merely looked at the latest linus/master build.
The result was a good one though, because basically Thomas' work got pushed from tip/rt/bkl
into tip/master, and can hopefully be pushed upstream during the next merge window.

Even if getting starting means just reviewing what is in rt/bkl and not yet in linus/master,
I think that would be positive. I'm sure Thomas will stomp on me if I start to annoy him. :)

Thanks

John
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