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Date: Mon, 31 Aug 2015 20:33:35 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>, Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        David Howells <dhowells@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Jonathan Corbet <corbet@lwn.net>
Subject: Re: wake_up_process implied memory barrier clarification
Message-ID: <20150831183335.GA26333@redhat.com>
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On 08/31, Boqun Feng wrote:
>
> Fair enough, I went too far. How about just a single paragraph saying
> that:
>
> The wake_up(), wait_event() and their friends have proper barriers in
> them, but these implicity barriers are only for the correctness for
> sleep and wakeup. So don't rely on these barriers for things that are
> neither wait-conditons nor task states.
>
> Is that OK to you?

Ask Paul ;) but personally I agree.

To me, the only thing a user should know about wake_up/try_to_wake_up
and barriers is that you do not need another barrier between setting
condition and waking up.

Oleg.