linux-kernel - Re: [PATCH tip/core/rcu 13/22] rcu: Fix grace-period hangs due to race with CPU offline

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Message-ID: <20180626174424.GK2494@hirez.programming.kicks-ass.net>
Date:   Tue, 26 Jun 2018 19:44:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     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 13/22] rcu: Fix grace-period hangs due to
 race with CPU offline

On Tue, Jun 26, 2018 at 10:10:39AM -0700, Paul E. McKenney wrote:
> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
> index 3def94fc9c74..6683da6e4ecc 100644
> --- a/kernel/rcu/tree.h
> +++ b/kernel/rcu/tree.h
> @@ -363,6 +363,10 @@ struct rcu_state {
>  	const char *name;			/* Name of structure. */
>  	char abbr;				/* Abbreviated name. */
>  	struct list_head flavors;		/* List of RCU flavors. */
> +
> +	spinlock_t ofl_lock ____cacheline_internodealigned_in_smp;

Are you really sure you didn't mean to use ____cacheline_aligned_in_smp
? This internode crap gives you full page alignment under certain rare
configs.