[PATCH v3 01/16] perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and deref

[Paolo Bonzini]

On 11/4/21 15:18, Sean Christopherson wrote:
> If I'm interpeting Paolo's suggestion
> correctly, he's pointing out that oustanding stores to the function pointers in
> @cbs need to complete before assigning a non-NULL pointer to perf_guest_cbs,
> otherwise a perf event handler may see a valid pointer with half-baked callbacks.
> 
> I think smp_store_release() with a comment would be appropriate, assuming my
> above interpretation is correct.
> 

Yes, exactly.  It should even be rcu_assign_pointer(), matching the 
synchronize_rcu() in patch 1 (and the change can be done in patch 1, too).

Paolo