linux-kernel - Re: question on read_barrier

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Message-ID: <1397747767.6428.4.camel@linux-fkkt.site>
Date:	Thu, 17 Apr 2014 17:16:07 +0200
From:	Oliver Neukum <oneukum@...e.de>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: question on read_barrier_depends

On Wed, 2014-04-16 at 11:26 -0400, Alan Stern wrote:

> In addition, the following code in kfifo_get() does this:
> 
> 			*(typeof(__tmp->type))__val = \
> 				(__is_kfifo_ptr(__tmp) ? \
> 				((typeof(__tmp->type))__kfifo->data) : \
> 				(__tmp->buf) \
> 				)[__kfifo->out & __tmp->kfifo.mask]; \
> 			smp_wmb(); \
> 			__kfifo->out++; \
> 
> It looks like the smp_wmb() should really be smp_mb(), because it 
> separates the _read_ for val from the _write_ of kfifo->out.

But where is kfifo->out read at all?

	Regards
		Oliver



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