On Mon, 15 Jan 2018, Mathieu Desnoyers wrote:
> +static int membarrier_shared_expedited(void)
> +{
> + int cpu;
> + bool fallback = false;
> + cpumask_var_t tmpmask;
> +
> + if (num_online_cpus() == 1)
> + return 0;
> +
> + /*
> + * Matches memory barriers around rq->curr modification in
> + * scheduler.
> + */
> + smp_mb(); /* system call entry is not a mb. */
> +
> + /*
> + * Expedited membarrier commands guarantee that they won't
> + * block, hence the GFP_NOWAIT allocation flag and fallback
> + * implementation.
> + */
> + if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) {
> + /* Fallback for OOM. */
> + fallback = true;
> + }
> +
> + cpus_read_lock();
> + for_each_online_cpu(cpu) {
> + struct task_struct *p;
> +
> + /*
> + * Skipping the current CPU is OK even through we can be
> + * migrated at any point. The current CPU, at the point
> + * where we read raw_smp_processor_id(), is ensured to
> + * be in program order with respect to the caller
> + * thread. Therefore, we can skip this CPU from the
> + * iteration.
> + */
> + if (cpu == raw_smp_processor_id())
> + continue;
> + rcu_read_lock();
> + p = task_rcu_dereference(&cpu_rq(cpu)->curr);
> + if (p && p->mm && (atomic_read(&p->mm->membarrier_state) &
> + MEMBARRIER_STATE_SHARED_EXPEDITED)) {
This does not make sense vs. the documentation:
> + * @MEMBARRIER_CMD_SHARED_EXPEDITED:
> + * Execute a memory barrier on all running threads
> + * part of a process which previously registered
> + * with MEMBARRIER_CMD_REGISTER_SHARED_EXPEDITED.
This should say:
> + * Execute a memory barrier on all running threads
> + * of all processes which previously registered
> + * with MEMBARRIER_CMD_REGISTER_SHARED_EXPEDITED.
And I really have to ask whether this should be named _GLOBAL_ instead of
_SHARED_.
Hmm?
Thanks,
tglx
