linux-kernel - Re: [PATCH tip/core/rcu 01/21] doc: READ_ONCE() now implies smp_barrier

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Date:   Mon, 4 Dec 2017 23:57:54 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
        edumazet@...gle.com, fweisbec@...il.com, oleg@...hat.com
Subject: Re: [PATCH tip/core/rcu 01/21] doc: READ_ONCE() now implies
 smp_barrier_depends()

On Mon, Dec 04, 2017 at 10:39:05PM +0000, David Howells wrote:
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > > Good point!  How about as shown in the updated patch below?
> > 
> > Humm, I thought the idea was to completely remove read_barrier_depends
> > from the lkmm and memory-barriers.txt, making it an Alpha implementation
> > detail.
> 
> memory-barriers.txt explains how the barriers used by the kernel work, amongst
> other things.

The thing is, read-barrier-depends will no longer be used. read-read
dependencies will henceforth be assumed to 'just work'.

> Don't forget, btw, that Blackfin uses it also.

We should delete that blackfin code, its beyond insane.