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Date: Fri, 18 Sep 2015 15:31:34 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Dmitry Vyukov <dvyukov@google.com>, ebiederm@xmission.com,
        Al Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>, mhocko@suse.cz,
        LKML <linux-kernel@vger.kernel.org>, ktsan@googlegroups.com,
        Kostya Serebryany <kcc@google.com>,
        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
Message-ID: <20150918133134.GB10241@redhat.com>
References: <1442496268-47803-1-git-send-email-dvyukov@google.com> <20150917160837.GA26050@redhat.com> <CACT4Y+YKmhz-+sugKt86CF2715YtoVz4ee+sRfDp2Wu==A4zPQ@mail.gmail.com> <20150917174456.GA30178@redhat.com> <CACT4Y+bnqMGjMV6FHHJWsx0YaxWmRqAM+YY7b5wz-7JmFBnwjA@mail.gmail.com> <20150917180919.GA32116@redhat.com> <20150918085156.GS3816@twins.programming.kicks-ass.net> <20150918132844.GA10241@redhat.com>
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Damn, sorry for noise,

On 09/18, Oleg Nesterov wrote:
>
> Now. In theory this this code is wrong:
>
> 	if (Y) {
> 		BUG_ON(X == 0);
> 	}

Of course without READ_ONCE() or barrier() in between this code
is buggy in any case. But I hope you understand what I tried to
say...

Oleg.