Re: call_function_many: fix list delete vs add race

[Benjamin Herrenschmidt]

On Mon, 2011-01-31 at 22:17 +0100, Peter Zijlstra wrote:
> That's wrong:
> 
>  ->foo =
>  LOCK
>  UNLOCK
>  ->bar =
> 
> can be re-ordered as:
> 
>  LOCK
>  ->bar =
>  ->foo =
>  UNLOCK

Can it ? I though UNLOCK had a write barrier semantic ? It does on power
at least :-) It should have since it shall prevent stores inside the
lock region to pass the store of the unlock itself anyways.

So yes, ->bar = can leak into the lock, as can ->foo =, but they can't
be re-ordered vs. each other because the implied barrier will keep ->foo
= in the same "domain" as the unlock itself.

Or do other archs do something really nasty here that don't provide this
guarantee ?

Cheers,
Ben.


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