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Message-ID: <20190606074849.GD3402@hirez.programming.kicks-ass.net>
Date: Thu, 6 Jun 2019 09:48:49 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc: rcu@...r.kernel.org, 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,
dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
oleg@...hat.com, joel@...lfernandes.org
Subject: Re: [PATCH tip/core/rcu 6/9] rcu: Upgrade sync_exp_work_done() to
smp_mb()
On Thu, May 30, 2019 at 08:00:12AM -0700, Paul E. McKenney wrote:
> The sync_exp_work_done() function uses smp_mb__before_atomic(), but
> there is no obvious atomic in the ensuing code. The ordering is
> absolutely required for grace periods to work correctly, so this
> commit upgrades the smp_mb__before_atomic() to smp_mb().
>
Did this commit want a Fixes: line? Such that robots can find the right
kernels to backport this to?
> Reported-by: Andrea Parri <andrea.parri@...rulasolutions.com>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
> ---
> kernel/rcu/tree_exp.h | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
> index 9c990df880d1..d969650a72c6 100644
> --- a/kernel/rcu/tree_exp.h
> +++ b/kernel/rcu/tree_exp.h
> @@ -259,8 +259,7 @@ static bool sync_exp_work_done(unsigned long s)
> {
> if (rcu_exp_gp_seq_done(s)) {
> trace_rcu_exp_grace_period(rcu_state.name, s, TPS("done"));
> - /* Ensure test happens before caller kfree(). */
> - smp_mb__before_atomic(); /* ^^^ */
> + smp_mb(); /* Ensure test happens before caller kfree(). */
> return true;
> }
> return false;
> --
> 2.17.1
>
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