On Wed, Nov 27, 2013 at 02:44:58PM +0100, Thomas Gleixner wrote: > On Wed, 27 Nov 2013, Russell King - ARM Linux wrote: > > > On Wed, Nov 27, 2013 at 01:32:31PM +0000, Russell King - ARM Linux wrote: > > > On Wed, Nov 27, 2013 at 02:29:41PM +0100, Thomas Gleixner wrote: > > > > Though the kobject is the only thing which has a delayed work embedded > > > > inside struct kmem_cache. And the debug object splat points at the > > > > kmem_cache_free() of the struct kmem_cache itself. That's why I > > > > assumed the wreckage around that place. And indeed: > > > > > > > > kmem_cache_destroy(s) > > > > __kmem_cache_shutdown(s) > > > > sysfs_slab_remove(s) > > > > .... > > > > kobject_put(&s->kobj) > > > > kref_put(&kobj->kref, kobject_release); > > > > kobject_release(kref) > > > > #ifdef CONFIG_DEBUG_KOBJECT_RELEASE > > > > schedule_delayed_work(&kobj->release) > > > > #else > > > > kobject_cleanup(kobj) > > > > #endif > > > > > > > > So in the CONFIG_DEBUG_KOBJECT_RELEASE=y case, schedule_delayed_work() > > > > _IS_ called which arms the timer. debugobjects catches the attempt to > > > > free struct kmem_cache which contains the armed timer. > > > > > > You fail to show where the free is in the above path. > > > > Right, there's a kmem_cache_free(kmem_cache, s); by the slob code > > after the above sequence, which is The Bug(tm). > > > > As I said, a kobject has its own lifetime. If you embed that into > > another structure, that structure inherits the lifetime of the kobject, > > which is from the point at which it's created to the point at which the > > kobject's release function is called. > > > > So no, the code here is buggy. The kobject debugging has yet again > > found a violation of the kobject lifetime rules. slub needs fixing. > > I leave that discussion to you, greg and the slub folks. /me grabs some popcorn from tglx It's really not that much of a discussion, Documentation/kobject.txt has said this for years, it's as if no one even reads documentation anymore... If you embed a kobject into a structure, you have to use the kobject for the reference counting of the structure, otherwise it's a bug. If you don't want to use a kobject to reference count the structure, don't embed it into it, use a pointer. Are "slabs" never freed in the slub allocator? Surely someone should have seen the huge "this kobject doesn't have a release function" error message that the kernel should have spit out for it? Just make the kobject "dynamic" instead of embedded in struct kmem_cache and all will be fine. I can't believe this code has been broken for this long. thanks, greg k-h -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>