On Thu, Dec 03, 2015 at 09:26:27PM +0100, Peter Zijlstra wrote:
> The best we can do is hardcode a variable name; maybe something like:
>
> #define smp_cond_acquire(ptr, expr) do { \
> typeof(*ptr) val; \
> while ((val = READ_ONCE(*ptr)), expr) \
> cpu_relax(); \
> smp_rmb(); /* ctrl + rmb := acquire */ \
> } while (0)
>
> Which would let us write:
>
> smp_cond_acquire(&lock->val.counter, !(val & _Q_LOCKED_PENDING_MASK));
So I'm thinking that might still be hard to use for you if the LDXR+WFE
has the regular LL/SC constraint of not allowing other loads in.
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