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

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Message-ID: <27944.1240595625@redhat.com>
Date:	Fri, 24 Apr 2009 18:53:45 +0100
From:	David Howells <dhowells@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	dhowells@...hat.com, Ingo Molnar <mingo@...e.hu>,
	torvalds@...l.org, 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

Oleg Nesterov <oleg@...hat.com> wrote:

> Suppose that "event_indicated = 1" leaks into try_to_wake_up() after we
> read p->state.

In that case, it's entirely possible that the smp_wmb() in try_to_wake_up()
should actually be an smp_mb(), but that on whichever arch patch:

	commit 04e2f1741d235ba599037734878d72e57cb302b5
	Author: Linus Torvalds <torvalds@...dy.linux-foundation.org>
	Date:   Sat Feb 23 18:05:03 2008 -0800
	Subject: Add memory barrier semantics to wake_up() & co

was tested on, it made no difference.

David
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