linux-kernel - Re: [PATCH] It may not be assumed that wake_up(), finish

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Message-ID: <20090423212434.GA20556@elte.hu>
Date:	Thu, 23 Apr 2009 23:24:34 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Howells <dhowells@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>, serue@...ibm.com,
	viro@...iv.linux.org.uk,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] It may not be assumed that wake_up(), finish_wait()
	and co. imply a memory barrier

* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Thu, 23 Apr 2009, David Howells wrote:
> > 
> > Well, Ingo's point is it could be left up to the caller of 
> > wake_up() to supply the barrier:

Well, i mainly reacted to your documentation patch which was 
incorrect as it said wake-up implies a _FULL_ memory barrier.

I also suggested that lockless code should have its barriers clearly 
documented and they should not really rely on kernel facilities 
acting as memory barriers.

Then i also suggested that maybe in the future we could remove the 
smp_wmb() from try_to_wake_up(). That was just an afterthought, and 
a rather stupid one at that, as Linus quickly noted :-)

	Ingo
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