linux-kernel - Re: [PATCH] IPMI: Fix some RCU problems

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Date:	Wed, 3 Jan 2007 13:22:32 -0800
From:	Andrew Morton <akpm@...l.org>
To:	minyard@....org
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Carol Hebert <cah@...ibm.com>,
	OpenIPMI Developers <openipmi-developer@...ts.sourceforge.net>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH] IPMI: Fix some RCU problems

On Wed, 3 Jan 2007 09:31:30 -0600
Corey Minyard <minyard@....org> wrote:

>   found:
> +	smp_rmb();
>  	/* Note that each existing user holds a refcount to the interface. */
>  	kref_get(&intf->refcount);
>  
> @@ -2761,6 +2763,7 @@
>  		kref_put(&intf->refcount, intf_free);
>  	} else {
>  		/* After this point the interface is legal to use. */
> +		smp_wmb(); /* Keep memory order straight for RCU readers. */
>  		intf->intf_num = i;
>  		mutex_unlock(&ipmi_interfaces_mutex);
>  		call_smi_watchers(i, intf->si_dev);
> @@ -3924,6 +3927,8 @@
>  			/* Interface was not ready yet. */
>  			continue;
>  
> +		smp_rmb();
> +

It's nice to always have a comment explaining the use of open-coded
barriers.  Because often the reader is left wondered what on earth it's
barriering against what on earth else.

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