linux-kernel - Re: [PATCH tip/core/rcu 01/14] rcu: Protect rcu_boost() lockless accesses with ACCESS

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Message-ID: <20150109135614.GI29390@twins.programming.kicks-ass.net>
Date:	Fri, 9 Jan 2015 14:56:14 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Davidlohr Bueso <dave@...olabs.net>, linux-kernel@...r.kernel.org,
	mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com,
	borntraeger@...ibm.com
Subject: Re: [PATCH tip/core/rcu 01/14] rcu: Protect rcu_boost() lockless
 accesses with ACCESS_ONCE()

On Fri, Jan 09, 2015 at 05:49:54AM -0800, Paul E. McKenney wrote:
> > That reminds me, I think the new conversion for stores will most likely
> > introduce silly arg bugs:
> > 
> > -       ACCESS_ONCE(a) = b;
> > +       ASSIGN_ONCE(b, a);
> 
> I was planning to do mine by hand for this sort of reason.
> 
> Or are you thinking of something more subtle than the case where
> "b" is an unparenthesized comma-separated expression?

I think he's revering to the wrong way around-ness of the thing.

Its a bit of a mixed bag on assignments, but for instance
rcu_assign_pointer() takes them the right way around, as does
atomic_set().

So yes, I think the ASSIGN_ONCE() thing got the arguments the wrong way
around.

We could maybe still change it, before its in too long ?
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