linux-kernel - Re: [patch] cpufreq: mark cpufreq_tsc() as core_initcall

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Message-ID: <20061118212542.GA235@oleg>
Date:	Sun, 19 Nov 2006 00:25:42 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Paul E. McKenney" <paulmck@...ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [patch] cpufreq: mark cpufreq_tsc() as core_initcall_sync

On 11/18, Alan Stern wrote:
>
> By the way, I think the fastpath for synchronize_srcu() should be safe, 
> now that you have added the memory barriers into srcu_read_lock() and 
> srcu_read_unlock().  You might as well try putting it in.

I still think the fastpath should do mb() unconditionally to be correct.

> Although now that I look at it again, you have forgotten to put smp_mb()
> after the atomic_inc() call and before the atomic_dec().

As I see it, currently we don't need this barrier because synchronize_srcu()
does synchronize_sched() before reading ->hardluckref.

But if we add the fastpath into synchronize_srcu() then yes, we need mb()
after atomic_inc().

Unless I totally confused :)

Oleg.

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