linux-kernel - Re: [PATCH] doc: Update wake_up() & co. memory-barrier guarantees

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Message-ID: <Pine.LNX.4.44L0.1806260949130.1589-100000@iolanthe.rowland.org>
Date:   Tue, 26 Jun 2018 09:49:57 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Andrea Parri <andrea.parri@...rulasolutions.com>
cc:     linux-kernel@...r.kernel.org, <linux-doc@...r.kernel.org>,
        Will Deacon <will.deacon@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Akira Yokosawa <akiyks@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH] doc: Update wake_up() & co. memory-barrier guarantees

On Tue, 26 Jun 2018, Andrea Parri wrote:

> > > -A write memory barrier is implied by wake_up() and co.  if and only if they
> > > -wake something up.  The barrier occurs before the task state is cleared, and so
> > > -sits between the STORE to indicate the event and the STORE to set TASK_RUNNING:
> > > +A general memory barrier is executed by wake_up() if it wakes something up.
> > > +If it doesn't wake anything up then a memory barrier may or may not be
> > > +executed; you must not rely on it.  The barrier occurs before the task state
> > > +is accessed, in part., it sits between the STORE to indicate the event and
> > > +the STORE to set TASK_RUNNING:
> > 
> > Minor suggestion: Instead of "in part.", how about "that is"?
> > 
> > (I generally find "in part." to be at least a little confusing,
> > probably because "part" is itself a word and "in part" is a 
> > reasonably common phrase in English.)
> 
> Mmh, the fact is that that "before the task state is accessed" does want
> to include the LOAD from ->state to check for the task state (recall the
> pattern in [1])...; how about if I expand "in part." to "in particular"?

That would be acceptable.

Alan