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SubjectRe: [PATCH tip/core/rcu 1/3] membarrier: Provide register expedited private command
On Wed, Oct 04, 2017 at 02:37:53PM -0700, Paul E. McKenney wrote:
> diff --git a/arch/powerpc/kernel/membarrier.c b/arch/powerpc/kernel/membarrier.c
> new file mode 100644
> index 000000000000..b0d79a5f5981
> --- /dev/null
> +++ b/arch/powerpc/kernel/membarrier.c
> @@ -0,0 +1,45 @@

> +void membarrier_arch_register_private_expedited(struct task_struct *p)
> +{
> + struct task_struct *t;
> +
> + if (get_nr_threads(p) == 1) {
> + set_thread_flag(TIF_MEMBARRIER_PRIVATE_EXPEDITED);
> + return;
> + }
> + /*
> + * Coherence of TIF_MEMBARRIER_PRIVATE_EXPEDITED against thread
> + * fork is protected by siglock.
> + */
> + spin_lock(&p->sighand->siglock);
> + for_each_thread(p, t)
> + set_ti_thread_flag(task_thread_info(t),
> + TIF_MEMBARRIER_PRIVATE_EXPEDITED);

I'm not sure this works correctly vs CLONE_VM without CLONE_THREAD.

> + spin_unlock(&p->sighand->siglock);
> + /*
> + * Ensure all future scheduler executions will observe the new
> + * thread flag state for this process.
> + */
> + synchronize_sched();

This relies on the flag being read inside rq->lock, right?

> +}

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