> Hello.
>
> Thank you for pointing out.
>
> Jun WANG wrote:
> > >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" ?
> >
> > In Document/RCU/whatisRCU.txt
> > Note that the value returned by rcu_dereference() is valid
> > only within the enclosing RCU read-side critical section.
> Excuse me, but I think "p" is used only between rcu_read_lock() and
> rcu_read_unlock().
> Is it illegal to use "ptr" after rcu_read_unlock() if "ptr" is obtained
> before rcu_read_unlock() ?
>
> Regards.
>
I'm sorry,I think I got your idea, if you do not need ptr in
my_task_that_may_sleep(), why you need to grab a reference to "ptr". If
your my_task_that_may_sleep() needs ptr, and according to the
>"memory region pointed by "ptr" never be removed." you say,
it is ok to use "ptr" after rcu_read_ulock(). The basic idea behind RCU
is to split updates into "removal" and "reclamation" phases. If you
memory region pointed by "ptr" will not "reclamation" in sleep, it is ok
Regards.
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