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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.
Fixes: 5a836bf6b09f ("mm: slub: move flush_cpu_slab() invocations __free_slab() invocations out of IRQ context")
Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: David Rientjes <rientjes@google.com>
Link: https://lore.kernel.org/all/YwOImVd+nRUsSAga@hyeyoo/
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
0495e337b7