linux-kernel - Re: [PATCH] slow_work_execute() needs mb() before test_bit(SLOW_WORK

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Message-ID: <20090416141510.GC6532@redhat.com>
Date:	Thu, 16 Apr 2009 16:15:10 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Howells <dhowells@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Serge Hallyn <serue@...ibm.com>,
	Steve Dickson <steved@...hat.com>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Daire Byrne <Daire.Byrne@...mestore.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] slow_work_execute() needs mb() before
	test_bit(SLOW_WORK_PENDING)

On 04/16, David Howells wrote:
>
> Oleg Nesterov <oleg@...hat.com> wrote:
>
> > But why do we need the barrier before clear_bit(SLOW_WORK_EXECUTING) ?
> > We do have one after test_and_clear_bit(SLOW_WORK_PENDING) above, and it
> > should be enough, no?
>
> No.  There lock is covering work->ops->execute(work) too, and that is after
> the clearance of SLOW_WORK_PENDING.  The UNLOCK-class barrier must go between
> execution and clearance of the execution lock bit.

Ah. Now I see.

It is still not clear to me whether we need a barrier after clear_bit_unlock.

Thanks David!

Oleg.

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