On 8/23/22 07:33, Vlastimil Babka wrote:
On 8/12/22 20:30, 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@xxxxxxxxxx>Thanks, added to slab.git for-6.0/fixes
Thanks for taking it. Cheers, Longman
