Messages in this thread | | | Date | Mon, 15 Aug 2022 10:01:50 -0400 | Subject | Re: [PATCH v3] mm/slab_common: Deleting kobject in kmem_cache_destroy() without holding slab_mutex/cpu_hotplug_lock | From | Waiman Long <> |
| |
On 8/13/22 14:25, Roman Gushchin wrote: > On Fri, Aug 12, 2022 at 02:30:33PM -0400, Waiman Long wrote: >> A circular locking problem is reported by lockdep due to the following >> circular locking dependency. >> >> +--> cpu_hotplug_lock --> slab_mutex --> kn->active --+ >> | | >> +-----------------------------------------------------+ >> >> The forward cpu_hotplug_lock ==> slab_mutex ==> kn->active dependency >> happens in >> >> kmem_cache_destroy(): cpus_read_lock(); mutex_lock(&slab_mutex); >> ==> sysfs_slab_unlink() >> ==> kobject_del() >> ==> kernfs_remove() >> ==> __kernfs_remove() >> ==> kernfs_drain(): rwsem_acquire(&kn->dep_map, ...); >> >> The backward kn->active ==> cpu_hotplug_lock dependency happens in >> >> kernfs_fop_write_iter(): kernfs_get_active(); >> ==> slab_attr_store() >> ==> cpu_partial_store() >> ==> flush_all(): cpus_read_lock() >> >> One way to break this circular locking chain is to avoid holding >> cpu_hotplug_lock and slab_mutex while deleting the kobject in >> sysfs_slab_unlink() which should be equivalent to doing a write_lock >> and write_unlock pair of the kn->active virtual lock. >> >> Since the kobject structures are not protected by slab_mutex or the >> cpu_hotplug_lock, we can certainly release those locks before doing >> the delete operation. >> >> Move sysfs_slab_unlink() and sysfs_slab_release() to the newly >> created kmem_cache_release() and call it outside the slab_mutex & >> cpu_hotplug_lock critical sections. There will be a slight delay >> in the deletion of sysfs files if kmem_cache_release() is called >> indirectly from a work function. >> >> Signed-off-by: Waiman Long <longman@redhat.com> > Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev> > > Thank you, Waiman! > Thanks for your suggestions that make this patch better.
Cheers, Longman
| |