linux-kernel - Re: [PATCH] fix misplaced mb() in rcu_enter/exit

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Date:	Mon, 17 Mar 2008 21:30:47 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	linux-rt-users@...r.kernel.org, mingo@...e.hu, ego@...ibm.com,
	dipankar@...ibm.com, tytso@...ibm.com, dvhltc@...ibm.com,
	akpm@...ux-foundation.org, josh@...edesktop.org,
	tglx@...utronix.de, niv@...ibm.com
Subject: Re: [PATCH] fix misplaced mb() in rcu_enter/exit_nohz()

On 03/16, Paul E. McKenney wrote:
> 
> In the process of writing up the mechanical proof of correctness for the
> dynticks/preemptable-RCU interface, I noticed misplaced memory barriers
> in rcu_enter_nohz() and rcu_exit_nohz().

Can't comment this patch, there is no rcu_enter_nohz() in my rcupreempt.h ;)

I'm not sure the code below is up to date, but what I have in
arch/s390/kernel/time.c is:

	stop_hz_timer:

		cpu_set(cpu, nohz_cpu_mask);
		
		if (rcu_needs_cpu(cpu) || local_softirq_pending()) {
			cpu_clear(cpu, nohz_cpu_mask);
			return;
		}

Don't we need smp_mb() after cpu_set() ?

Oleg.

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