Re: [PATCH v3] slub: fix false-positive lockdep warning infree_partial()

From: Christoph Lameter
Date: Wed Feb 05 2014 - 15:42:41 EST

On Wed, 5 Feb 2014, Steven Rostedt wrote:

> Really? We are adding a spin lock for a case where it is not needed just to
> quiet lockdep?

Well its a very rarely used code path. Doesnt matter performance wise
since a slab cache should have no objects when its going to be removed.

> Now if it really isn't needed, then why don't we do the following instead of
> adding the overhead of taking a lock?
> static inline
> __remove_partial(struct kmem_cache_node *n, struct page *page)
> {
> list_del(&page->lru);
> n->nr_partial--;
> }
> static inline remove_partial(struct kmem_cache_node *n,
> struct page *page)
> {
> lockdep_assert_held(&n->list_lock);
> __remove_partial(n, page);
> }
> And then just call __remove_partial() where we don't need to check if the
> lock is held or not with a big comment to it.
> That, IMNSHO, is a much better solution

Ok with me. It just adds another variant of remove_partial.

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