Messages in this thread | | | Date | Mon, 6 Feb 2023 17:04:07 +0100 | From | Sebastian Andrzej Siewior <> | Subject | Re: [PATCH v4] kernel/fork: beware of __put_task_struct calling context |
| |
On 2023-02-06 16:27:12 [+0100], Oleg Nesterov wrote: > On 02/06, Sebastian Andrzej Siewior wrote: > > > > On 2023-02-06 10:04:47 [-0300], Wander Lairson Costa wrote: > > > > > @@ -857,6 +857,29 @@ void __put_task_struct(struct task_struct *tsk) > > … > > > +void __put_task_struct(struct task_struct *tsk) > > > +{ > > > + if (IS_ENABLED(CONFIG_PREEMPT_RT) && (!preemptible() || !in_task())) > > > > Is it safe to use the rcu member in any case? > > I thinks it is safe but deserves a comment. I guess Wander misunderstood > me when I asked him to do this... > > __put_task_struct() is called when refcount_dec_and_test(&t->usage) succeeds. > > This means that it can't "conflict" with put_task_struct_rcu_user() which > abuses ->rcu the same way; rcu_users has a reference so task->usage can't > be zero after rcu_users 1 -> 0 transition.
Sounds good.
> > If so why not use it > > unconditionally? > > performance ?
All the free() part is moved from the caller into rcu.
> > And... I still don't like the name of delayed_put_task_struct_rcu() to me > ___put_task_struct_rcu() looks a bit less confusing, note that we already > have delayed_put_task_struct(). But this is minor.
So if we do it unconditionally then we could get rid of put_task_struct_rcu_user(). Otherwise we could use put_task_struct_rcu_user() in that timer callback because it will lead to lockdep warnings once printk is fixed.
> Oleg. Sebastian
| |