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From: David Howells <dhowells@redhat.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: dhowells@redhat.com, Oleg Nesterov <oleg@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Trond.Myklebust@netapp.com, serue@us.ibm.com, steved@redhat.com,
	viro@zeniv.linux.org.uk,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Nick Piggin <nickpiggin@yahoo.com.au>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Document that wake_up(), complete() and co. imply a full memory barrier
Date: Wed, 22 Apr 2009 16:12:06 +0100	[thread overview]
Message-ID: <4664.1240413126@redhat.com> (raw)
In-Reply-To: <20090422135134.GA5249@elte.hu>

Ingo Molnar <mingo@elte.hu> wrote:

> No. They dont generally imply a full memory barrier versus any
> arbitrary prior (or following) memory access.
>
> try_to_wake_up() has an smp_wmb() so it is a write memory barrier
> (but not necessarily a read memory barrier). Otherwise there are
> spinlocks there but spinlocks are not explicit 'full memory
> barriers'.

Blech.  That's a good point LOCK...UNLOCK does not imply a full barrier.

So we can't assume that complete(), wake_up() and co. imply any barriers.

All we can assume is that try_to_wake_up() implies a write barrier, but we
can't assume that that will be called via __wake_up_common().

David

  parent reply	other threads:[~2009-04-22 15:13 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-04-13 18:17 [PATCH] slow_work_thread() should do the exclusive wait Oleg Nesterov
2009-04-13 19:03 ` Trond Myklebust
2009-04-13 19:14   ` Oleg Nesterov
2009-04-13 21:40   ` David Howells
2009-04-13 21:48     ` Oleg Nesterov
2009-04-13 21:57       ` Trond Myklebust
2009-04-13 22:24         ` Oleg Nesterov
2009-04-15 23:27           ` Andrew Morton
2009-04-16  9:10             ` David Howells
2009-04-16 14:33               ` Oleg Nesterov
2009-04-22 13:37                 ` [PATCH] Document that wake_up(), complete() and co. imply a full memory barrier David Howells
2009-04-22 13:51                   ` Ingo Molnar
2009-04-22 14:39                     ` Oleg Nesterov
2009-04-22 14:56                       ` Ingo Molnar
2009-04-22 15:07                         ` Oleg Nesterov
2009-04-22 15:12                     ` David Howells [this message]
2009-04-22 15:19                       ` Ingo Molnar
2009-04-22 16:23                       ` David Howells
2009-04-22 17:57                         ` Ingo Molnar
2009-04-23 16:32                           ` [PATCH] It may not be assumed that wake_up(), finish_wait() and co. imply a " David Howells
2009-04-23 16:55                             ` Oleg Nesterov
2009-04-24 11:46                               ` David Howells
2009-04-24 15:08                                 ` Paul E. McKenney
2009-04-24 17:08                                   ` Oleg Nesterov
2009-04-24 17:43                                     ` Paul E. McKenney
2009-04-24 17:48                                   ` David Howells
2009-04-24 18:06                                     ` Paul E. McKenney
2009-04-28 10:18                                       ` David Howells
2009-04-28 13:00                                         ` Paul E. McKenney
2009-04-24 17:28                                 ` Oleg Nesterov
2009-04-24 17:53                                   ` David Howells
2009-04-24 18:30                                     ` Oleg Nesterov
2009-04-23 17:07                             ` Linus Torvalds
2009-04-23 20:35                               ` David Howells
2009-04-23 21:12                                 ` Linus Torvalds
2009-04-23 21:24                                   ` Ingo Molnar
2009-04-23 16:36                           ` [PATCH] Document that wake_up(), complete() and co. imply a full " Oleg Nesterov
2009-04-23 20:37                             ` David Howells
2009-04-23 16:00             ` [PATCH] slow_work_thread() should do the exclusive wait David Howells
2009-04-23 16:18               ` Oleg Nesterov
2009-04-13 21:35 ` David Howells

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