On Thu, Mar 19, 2015 at 01:25:36PM +0100, Peter Zijlstra wrote:
> +static struct qspinlock **pv_hash(struct qspinlock *lock)
> +{
> + u32 hash = hash_ptr(lock, PV_LOCK_HASH_BITS);
> + struct pv_hash_bucket *hb, *end;
> +
> + if (!hash)
> + hash = 1;
> +
> + hb = &__pv_lock_hash[hash_align(hash)];
> + for (;;) {
> + for (end = hb + PV_HB_PER_LINE; hb < end; hb++) {
> + if (cmpxchg(&hb->lock, NULL, HB_RESERVED)) {
That should be: !cmpxchg(), bit disturbing that that booted.
> + WRITE_ONCE(hb->cpu, smp_processor_id());
> + /*
> + * Since we must read lock first and cpu
> + * second, we must write cpu first and lock
> + * second, therefore use HB_RESERVE to mark an
> + * entry in use before writing the values.
> + *
> + * This can cause hb_hash_find() to not find a
> + * cpu even though _Q_SLOW_VAL, this is not a
> + * problem since we re-check l->locked before
> + * going to sleep and the unlock will have
> + * cleared l->locked already.
> + */
> + smp_wmb(); /* matches rmb from pv_hash_find */
> + WRITE_ONCE(hb->lock, lock);
> + goto done;
> + }
> + }
> +
> + hash = lfsr(hash, PV_LOCK_HASH_BITS);
> + hb = &__pv_lock_hash[hash_align(hash)];
> + }
> +
> +done:
> + return &hb->lock;
> +}
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