Messages in this thread | | | Subject | Re: [PATCH] slub: Fix sysfs duplicate filename creation when slub_debug=O | From | Miles Chen <> | Date | Wed, 8 Nov 2017 13:32:18 +0800 |
| |
On Tue, 2017-11-07 at 09:22 -0600, Christopher Lameter wrote: > On Tue, 7 Nov 2017, miles.chen@mediatek.com wrote: > > > When slub_debug=O is set. It is possible to clear debug flags > > for an "unmergeable" slab cache in kmem_cache_open(). > > It makes the "unmergeable" cache became "mergeable" in sysfs_slab_add(). > > Right but that is only if disable_higher_order_debug is set.
yes
> > > These caches will generate their "unique IDs" by create_unique_id(), > > but it is possible to create identical unique IDs. In my experiment, > > sgpool-128, names_cache, biovec-256 generate the same ID ":Ft-0004096" > > and the kernel reports "sysfs: cannot create duplicate filename > > '/kernel/slab/:Ft-0004096'". > > Ok then the aliasing failed for some reason. The creation of the unique id > and the alias detection needs to be in sync otherwise duplicate filenames > are created. What is the difference there?
The aliasing failed because find_mergeable() returns if (flags & SLAB_NEVER_MERGE) is true. So we do not go to search for alias caches.
__kmem_cache_alias() find_mergeable() kmem_cache_flags() --> setup flag by the slub_debug if (flags & SLAB_NEVER_MERGE) return NULL; ... search alias logic...
The flags maybe changed if disable_higher_order_debug=1. So the unmergeable cache becomes mergeable later.
> > The clearing of the DEBUG_METADATA_FLAGS looks ok to me. kmem_cache_alias > should do the same right? > Yes, I think clearing DEBUG_METADATA flags in kmem_cache_alias is another solution for this issue.
We will need to do calculate_sizes() by using original flags and compare the order of s->size and s->object_size when disable_higher_order_debug=1.
| |