Re: [RFC][PATCH 2/5] mutex: Use p->oncpu for the adaptive spin

[Oleg Nesterov]

On 12/16, Peter Zijlstra wrote:
>
> So yea, I think we can simplify all this even further, but we do need a
> smp_rmb() in between those two checks, hmm, and RCU.

I am not sure we need rmb() or even read_barrier_depends(), I think
the simple barrier() should be enough. Although rcu_dereference()
may be more clean.

We don't really care about the "correct" result of *owner. All we need,
we should ensure it is safe to dereference this address. If CPU itself
does something like "readahead" before we verified "lock->owner == owner"
under RCU lock, this shouldn't lead to the fault.

Oleg.

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