Sleeping in RCU list traversal

Tetsuo Handa
2007-10-07T10:38:50Z

Hello.

Peter Zijlstra wrote:
> > Can I sleep between rcu_read_lock() and rcu_read_unlock() ?
> > As far as I saw, rcu_read_lock() makes in_atomic() true, so I think I can't sleep.
> You can indeed not sleep in an rcu_read_lock() section. However, you
> could grab a reference on an item, stop the iteration, drop
> rcu_read_lock. Do you thing, re-acquire rcu_read_lock(), drop the ref,
> and continue the iteration.

Something like this?

rcu_read_lock();
list_for_each_rcu(p, ...) {
ptr = list_entry(p, struct ..., list);
/* Grab a reference to "ptr". */
rcu_read_unlock();
my_task_that_may_sleep(ptr);
rcu_read_lock();
/* Drop a reference to "ptr". */
}
rcu_read_unlock();

Regarding my case, memory region pointed by "ptr" never be removed.
Do I need to grab a reference to "ptr" ?

Regards.