linux-kernel - Re: [PATCH] kernel: fix data race in put

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Message-ID: <20150918093355.GK3604@twins.programming.kicks-ass.net>
Date:	Fri, 18 Sep 2015 11:33:55 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Will Deacon <will.deacon@....com>
Cc:	Dmitry Vyukov <dvyukov@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"ebiederm@...ssion.com" <ebiederm@...ssion.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	"mhocko@...e.cz" <mhocko@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>,
	"ktsan@...glegroups.com" <ktsan@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Hans Boehm <hboehm@...gle.com>
Subject: Re: [PATCH] kernel: fix data race in put_pid

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..


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