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Message-ID: <20190328162641.GC19441@redhat.com>
Date: Thu, 28 Mar 2019 17:26:42 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Jann Horn <jannh@...gle.com>
Cc: Joel Fernandes <joel@...lfernandes.org>,
"Paul E. McKenney" <paulmck@...ux.ibm.com>,
Kees Cook <keescook@...omium.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
LKML <linux-kernel@...r.kernel.org>,
Android Kernel Team <kernel-team@...roid.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Matthew Wilcox <willy@...radead.org>,
Michal Hocko <mhocko@...e.com>,
"Reshetova, Elena" <elena.reshetova@...el.com>
Subject: Re: [PATCH] Convert struct pid count to refcount_t
On 03/28, Jann Horn wrote:
>
> Since we're just talking about RCU stuff now, adding Paul McKenney to
> the thread.
Since you added Paul let me add more confusion to this thread ;)
There were some concerns about the lack of barriers in put_pid(), but I can't
find that old discussion and I forgot the result of that discussion...
Paul, could you confirm that this code
CPU_0 CPU_1
X = 1; if (READ_ONCE(Y))
mb(); X = 2;
Y = 1; BUG_ON(X != 2);
is correct? I think it is, control dependency pairs with mb(), right?
If not, then put_pid() needs atomic_read_acquire() as it was proposed in that
discussion.
Oleg.
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