Messages in this thread | | | Date | Fri, 4 Jan 2019 18:37:16 +0000 | From | Catalin Marinas <> | Subject | Re: [PATCH] mm: kmemleak: Turn kmemleak_lock to spin lock and RCU primitives |
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On Fri, Jan 04, 2019 at 10:29:13PM +0800, zhe.he@windriver.com wrote: > It's not necessary to keep consistency between readers and writers of > kmemleak_lock. RCU is more proper for this case. And in order to gain better > performance, we turn the reader locks to RCU read locks and writer locks to > normal spin locks.
This won't work.
> @@ -515,9 +515,7 @@ static struct kmemleak_object *find_and_get_object(unsigned long ptr, int alias) > struct kmemleak_object *object; > > rcu_read_lock(); > - read_lock_irqsave(&kmemleak_lock, flags); > object = lookup_object(ptr, alias); > - read_unlock_irqrestore(&kmemleak_lock, flags);
The comment on lookup_object() states that the kmemleak_lock must be held. That's because we don't have an RCU-like mechanism for removing removing objects from the object_tree_root:
> > /* check whether the object is still available */ > if (object && !get_object(object)) > @@ -537,13 +535,13 @@ static struct kmemleak_object *find_and_remove_object(unsigned long ptr, int ali > unsigned long flags; > struct kmemleak_object *object; > > - write_lock_irqsave(&kmemleak_lock, flags); > + spin_lock_irqsave(&kmemleak_lock, flags); > object = lookup_object(ptr, alias); > if (object) { > rb_erase(&object->rb_node, &object_tree_root); > list_del_rcu(&object->object_list); > } > - write_unlock_irqrestore(&kmemleak_lock, flags); > + spin_unlock_irqrestore(&kmemleak_lock, flags);
So here, while list removal is RCU-safe, rb_erase() is not.
If you have time to implement an rb_erase_rcu(), than we could reduce the locking in kmemleak.
-- Catalin
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