Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

On Fri, Aug 17, 2007 at 11:54:33AM -0700, Arjan van de Ven wrote:

On Fri, 2007-08-17 at 12:50 -0600, Chris Friesen wrote:

quoted

Linus Torvalds wrote:

quoted

 - in other words, the *only* possible meaning for "volatile" is a purely 
   single-CPU meaning. And if you only have a single CPU involved in the 
   process, the "volatile" is by definition pointless (because even 
   without a volatile, the compiler is required to make the C code appear 
   consistent as far as a single CPU is concerned).

I assume you mean "except for IO-related code and 'random' values like 
jiffies" as you mention later on?  I assume other values set in 
interrupt handlers would count as "random" from a volatility perspective?

quoted

So anybody who argues for "volatile" fixing bugs is fundamentally 
incorrect. It does NO SUCH THING. By arguing that, such people only show 
that you have no idea what they are talking about.

What about reading values modified in interrupt handlers, as in your 
"random" case?  Or is this a bug where the user of atomic_read() is 
invalidly expecting a read each time it is called?

the interrupt handler case is an SMP case since you do not know
beforehand what cpu your interrupt handler will run on.

With the exception of per-CPU variables, yes.

							Thanx, Paul