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Date: Fri, 18 Sep 2015 11:33:55 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Will Deacon <will.deacon@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>, Oleg Nesterov <oleg@redhat.com>,
        "ebiederm@xmission.com" <ebiederm@xmission.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
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        Andrey Konovalov <andreyknvl@google.com>,
        Alexander Potapenko <glider@google.com>,
        Hans Boehm <hboehm@google.com>
Subject: Re: [PATCH] kernel: fix data race in put_pid
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On Fri, Sep 18, 2015 at 10:28:20AM +0100, Will Deacon wrote:
> > #define atomic_read_ctrl(v) READ_ONCE_CTRL(&(v)->counter)
> 
> Funnily enough, I had this exact same discussion off-list yesterday
> afternoon, since I wrote some code relying on a ctrl dependency from
> an atomic_read to an atomic_xchg_relaxed.
> 
> So I guess I'm for the addition, but at the same time, could we make
> atomic_read and atomic_set generic too?

Nope (having just gone through them), there's a few archs that implement
them in asm or even outright function calls (see blackfin, metag,
powerpc, s390).

That said, the patch I just send should see them all be at least
{READ,WRITE}_ONCE, the asm one obviously qualify for that etc..