Re: allow preemption in check_task_state

[Peter Zijlstra]

On Mon, Feb 10, 2014 at 06:17:12PM +0100, Nicholas Mc Guire wrote:
> maybe I'm missing/missunderstanding something here but
> pi_unlock -> arch_spin_unlock is a full mb() 

Nope, arch_spin_unlock() on x86 is a single add[wb] without LOCK prefix.

The lock and unlock primitives are in general specified to have ACQUIRE
resp. RELEASE semantics.

See Documentation/memory-barriers.txt for far too much head-hurting
details.
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