Re: [PATCH v3 3/3] md: protect md_thread with rcu

[Yu Kuai <yukuai1@huaweicloud.com>]

Hi, Logan!

在 2023/03/31 3:35, Logan Gunthorpe 写道:
> 
> A couple points:
> 
> I don't think we need a double pointer here. rcu_dereference() doesn't
> actually do anything but annotate the fact that we are accessing a
> pointer protected by rcu. It does require annotations on that pointer
> (__rcu) which is checked by sparse (I suspect this patch will produce a
> lot of sparse errors from kbuild bot).
> 
> I think all we need is:
> 
> void md_wakeup_thread(struct md_thread __rcu *rthread)
> {
> 	struct md_thread *thread;
>     	
> 	rcu_read_lock();
> 	thread = rcu_dereference(rthread);
> 	...
> 	rcu_read_unlock();
> 	
> }
> 
> The __rcu annotation will have to be added to all the pointers this
> function is called on as well as to md_register_thread() and
> md_unregister_thread(). And anything else that uses those pointers.
> Running sparse on the code and eliminating all new errors for the patch
> is important.

Yes, you're right, I'll remove patch 2 and update patch 3. And I'll try
to run sparse before sending the new version.

Thanks,
Kuai