Re: why are some atomic_t's not volatile, while most are?

[Chris Snook]

Chris Friesen wrote:
> Chris Snook wrote:
>
> > This is not a problem, since indirect references will cause the CPU to 
> > fetch the data from memory/cache anyway.
>
> Isn't Zan's sample code (that shows the problem) already using indirect 
> references?

Yeah, I misinterpreted his conclusion.  I thought about this for a 
while, and realized that it's perfectly legal for the compiler to re-use 
a value obtained from atomic_read.  All that matters is that the read 
itself was atomic.  The use (or non-use) of the volatile keyword is 
really more relevant to the other atomic operations.  If you want to 
guarantee a re-read from memory, use barrier().  This, incidentally, 
uses volatile under the hood.

	-- Chris
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/