On Mon, Jul 13, 2015 at 03:48:28PM +0200, Peter Zijlstra wrote: > @@ -239,9 +265,16 @@ static void pv_wait_head(struct qspinloc > cpu_relax(); > } > > - WRITE_ONCE(pn->state, vcpu_halted); > + /* > + * Either pv_kick_node() advanced us and ->state is already > + * vcpu_hashed and this store is superfluous, or this is the > + * first in which case the below cmpxchg() provides the > + * required barriers. > + */ > + WRITE_ONCE(pn->state, vcpu_hashed);
The easier option is of course to just move this store into the branch below. That immediately clarifies the logic and avoids the superfluous store. > if (!lp) { /* ONCE */ > lp = pv_hash(lock, pn); > + > /* > * lp must be set before setting _Q_SLOW_VAL > * -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/