Re: [patch 134/149] x86, paravirt: Add a global synchronization point for pvclock

[H. Peter Anvin]

On 07/14/2010 10:34 AM, Jeremy Fitzhardinge wrote:
> On 07/14/2010 10:30 AM, H. Peter Anvin wrote:
>> If gcc ever starts reordering volatile operations, including "asm
>> volatile", the kernel will break, and will be unfixable.  Just about
>> every single driver will break.  All over the kernel we're explicitly or
>> implicitly making the assumption that volatile operations are strictly
>> ordered by the compiler with respect to each other.
> 
> Can you give an example?  All the cases I've seen rely on the ordering
> properties of "memory" clobbers, which is sound.  (And volatile
> variables are a completely unrelated issue, of course.)
> 

I/O ports, for example.

	-hpa

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