> +/*
> + * hpref_hp_get: Obtain a reference to a stable object, protected either
> + * by hazard pointer (fast-path) or using reference
> + * counter as fall-back.
> + */
> +static inline
> +bool hpref_hp_get(struct hpref_node **node_p, struct hpref_ctx *ctx)
> +{
> + int cpu = rseq_current_cpu_raw();
> + struct hpref_percpu_slots *cpu_slots = rseq_percpu_ptr(hpref_percpu_slots, cpu);
> + struct hpref_slot *slot = &cpu_slots->slots[cpu_slots->current_slot];
> + bool use_refcount = false;
> + struct hpref_node *node, *node2;
> + unsigned int next_slot;
> +
> +retry:
> + node = uatomic_load(node_p, CMM_RELAXED);
> + if (!node)
> + return false;
> + /* Use rseq to try setting current slot hp. Store B. */
> + if (rseq_load_cbne_store__ptr(RSEQ_MO_RELAXED, RSEQ_PERCPU_CPU_ID,
> + (intptr_t *) &slot->node, (intptr_t) NULL,
> + (intptr_t) node, cpu)) {
> + slot = &cpu_slots->slots[HPREF_EMERGENCY_SLOT];
Can @cpu be possibly changed? if it can, it seems @cpu and @cpu_slots
should be updated first.
> + use_refcount = true;
> + /*
> + * This may busy-wait for another reader using the
> + * emergency slot to transition to refcount.
> + */
> + caa_cpu_relax();
> + goto retry;
> + }
