Re: [PATCH 01/11] mm/slab: hold a slab_mutex when calling __kmem_cache_shrink()

From: Nikolay Borisov
Date: Thu Mar 31 2016 - 06:53:23 EST

On 03/28/2016 08:26 AM, js1304@xxxxxxxxx wrote:
> From: Joonsoo Kim <>
> Major kmem_cache metadata in slab subsystem is synchronized with
> the slab_mutex. In SLAB, if some of them is changed, node's shared
> array cache would be freed and re-populated. If __kmem_cache_shrink()
> is called at the same time, it will call drain_array() with n->shared
> without holding node lock so problem can happen.
> We can fix this small theoretical race condition by holding node lock
> in drain_array(), but, holding a slab_mutex in kmem_cache_shrink()
> looks more appropriate solution because stable state would make things
> less error-prone and this is not performance critical path.
> In addtion, annotate on SLAB functions.

Just a nit but would it not be better instead of doing comment-style
annotation to use lockdep_assert_held/_once. In both cases for someone
to understand what locks have to be held will go and read the source. In
my mind it's easier to miss a comment line, rather than the
lockdep_assert. Furthermore in case lockdep is enabled a locking
violation would spew useful info to dmesg.