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Subject: Re: [Fwd: [patch] media video cx23888 driver: ported to new kfifo
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From: Stefani Seibold <stefani@seibold.net>
To: Andrew Morton <akpm@linux-foundation.org>
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Date: Fri, 18 Dec 2009 23:09:26 +0100
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Am Freitag, den 18.12.2009, 14:00 -0800 schrieb Andrew Morton:
> On Fri, 18 Dec 2009 22:57:22 +0100
> Stefani Seibold <stefani@seibold.net> wrote:
> 
> > But kfifo_len() did not
> > requiere a lock in my opinion. It is save to use without a look. 
> 
> What do you mean by this?  Safe in general, or safe in this particular driver?
> 

Safe until you don't call kfifo_reset(). kfifo_reset() is evil, because
it it the only function which breaks the single read/writer concept. 

This function modifies the in and the out fifo counters. Thats why i
introduced the kfifo_reset_out() function, which set the out to the
value of in, which means the fifo is empty. This function can be call
from the receiver of a fifo without locking.  

Stefani