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From: Oleg Nesterov <>
To: David Howells <>
Cc: Andrew Morton <>,
	Dmitry Torokhov <>,
	Jiri Pirko <>,
	"Paul E. McKenney" <>,
	Peter Zijlstra <>,
Subject: Re: [RFC,PATCH] workqueues: turn queue_work() into the "barrier" for work->func()
Date: Wed, 12 Nov 2008 12:58:04 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 11/11, David Howells wrote:
> Oleg Nesterov <> wrote:
> > I think the caller of queue_work() has all rights to expect that
> > the next invocation of work_func() must see "VAR == 1", but this
> > is not true if the work is already pending.
> As you said, queue_work() does test_and_set_bit() which implies smp_mb()
> either side of the function, so you're half way there, and run_workqueue()
> calls spin_unlock_irq() just before calling work_clear_pending()...  So might
> it make sense to move the work_clear_pending() into locked section?  Or would
> that require an smp_mb__before_clear_bit()?

This can't really help, afaics. We still need mb() between clear_bit(_PENDING)
and LOAD(VAR). Because unlock() is the "one way" barrier, LOAD(VAR) can leak
into the critical section, and it can be re-ordered with clear_bit() inside
the critical section.


      reply	other threads:[~2008-11-12 10:58 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-11-11 20:33 Oleg Nesterov
2008-11-11 22:46 ` David Howells
2008-11-12 11:58   ` Oleg Nesterov [this message]

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