Re: [PATCH tip/core/rcu 1/3] membarrier: Provide register expedited private command

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

----- On Oct 5, 2017, at 8:24 AM, Peter Zijlstra peterz@infradead.org wrote:

> On Thu, Oct 05, 2017 at 02:12:50PM +0200, Peter Zijlstra wrote:
>> 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.
> 
> Also, for easier reading I would suggest putting { } around the block.

Will do, thanks,

Mathieu

> 
>> > +	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?
>> 
> > > +}

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com