Re: [patch] spinlocks: remove 'volatile'

Linus Torvalds
2006-07-06T18:01:07Z

On Thu, 6 Jul 2006, linux-os (Dick Johnson) wrote:
>
> Linus, you may have been reading too many novels.
>
> If I have some code that does:
>
> extern int spinner;
>
> funct(){
> while(spinner)
> ;
>
> The 'C' compiler has no choice but to actually make that memory access
> and read the variable because the variable is in another module (a.k.a.
> file).

You don't know how C works, do you?

You also have no idea of what out-of-order memory accesses do to OS code,
right?

THE FACT IS, "volatile" IS USELESS, BADLY DEFINED, AND AN ALMOST
COMPLETELY SURE SIGN OF BUGS.

Go on, do your own OS, and try to use "volatile" in it as the
serialization abstraction. I personally will guarantee that you will fail.
But hey, you can prove me wrong.

In the meantime, in Linux, "volatile" is considered a bug in any but the
two special cases I already mentioned.

Linus