Messages in this thread | | | Date | Tue, 16 Nov 2010 14:04:13 +0100 | From | Oleg Nesterov <> | Subject | Re: [RFC/RFT PATCH v3] sched: automated per tty task groups |
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On 11/15, Mike Galbraith wrote: > > On Mon, 2010-11-15 at 13:57 +0100, Oleg Nesterov wrote: > > > And the exiting task can do a lot before it disappears, probably > > we shouldn't ignore ->autogroup.
I don't really understand what makes the exiting task different, but OK.
However, I must admit I dislike this check. Because, looking at this code, it is not clear why do we check PF_EXITING. It looks as if it is needed for correctness.
OK, this is minor. I think the patch is correct, just one nit below.
> > It can't protect the change of signal->autogroup, multiple callers > > can use different rq's. > > Guaranteed live ->autogroup should be good enough for heuristic use, and > had better be so. Having to take ->siglock in the fast path would kill > using ->signal.
Yes, sure, rq->lock should ensure signal->autogroup can't go away. (even if it can be changed under us). And it does, we are moving all threads before kref_put().
> +static void > +autogroup_move_group(struct task_struct *p, struct autogroup *ag) > +{ > + struct autogroup *prev; > + struct task_struct *t; > + > + prev = p->signal->autogroup; > + if (prev == ag) > + return; > + > + p->signal->autogroup = autogroup_kref_get(ag); > + sched_move_task(p); > + > + rcu_read_lock(); > + list_for_each_entry_rcu(t, &p->thread_group, thread_group) { > + sched_move_task(t); > + } > + rcu_read_unlock(); > + > + autogroup_kref_put(prev); > +}
Well, this looks a bit strange (but correct).
We are changing ->autogroup assuming the caller holds ->siglock. But if we hold ->siglock we do not need rcu_read_lock() to iterate over the thread_group, we can just do
p->signal->autogroup = autogroup_kref_get(ag);
t = p; do { sched_move_task(t); } while_each_thread(p, t);
Again, this is minor, I won't insist.
Oleg.
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