Messages in this thread | | | Date | Mon, 6 Feb 2023 17:27:58 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH v4] kernel/fork: beware of __put_task_struct calling context |
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On 02/06, Sebastian Andrzej Siewior wrote: > > On 2023-02-06 16:27:12 [+0100], Oleg Nesterov wrote: > > > > If so why not use it > > > unconditionally? > > > > performance ? > > All the free() part is moved from the caller into rcu.
sorry, I don't understand,
> > > > > 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().
Yes. But the whole purpose of rcu_users is that we want to avoid the unconditional rcu grace period before free_task() ?
Just in case... please note that delayed_put_task_struct() delays refcount_sub(t->usage), not free_task().
Why do we need this? Consider
rcu_read_lock();
task = find-task-in-rcu-protected-list;
// Safe, task->usage can't be zero get_task_struct(task);
rcu_read_unlock();
> Otherwise we could use put_task_struct_rcu_user() in that timer > callback because it will lead to lockdep warnings once printk is fixed.
IIUC there are more in-atomic callers of put_task_struct(). But perhaps I misunderstood you...
Oleg.
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