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

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Date:	Thu, 16 Apr 2009 10:43:42 +0100
From:	David Howells <dhowells@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	dhowells@...hat.com, 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)

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.

David
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