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mm/slab_common: Deleting kobject in kmem_cache_destroy() without holding slab_mutex/cpu_hotplug_lock 

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: 5a836bf6b0 ("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>
This commit is contained in:
Waiman Long 2022-08-12 14:30:33 -04:00 committed by Vlastimil Babka
parent 1c23f9e627
commit 0495e337b7
1 changed files with 29 additions and 16 deletions
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45
mm/slab_common.c
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@ -392,6 +392,28 @@ kmem_cache_create(const char *name, unsigned int size, unsigned int align,
}
EXPORT_SYMBOL(kmem_cache_create);
#ifdef SLAB_SUPPORTS_SYSFS
/*
* For a given kmem_cache, kmem_cache_destroy() should only be called
* once or there will be a use-after-free problem. The actual deletion
* and release of the kobject does not need slab_mutex or cpu_hotplug_lock
* protection. So they are now done without holding those locks.
*
* Note that there will be a slight delay in the deletion of sysfs files
* if kmem_cache_release() is called indrectly from a work function.
*/
static void kmem_cache_release(struct kmem_cache *s)
{
sysfs_slab_unlink(s);
sysfs_slab_release(s);
}
#else
static void kmem_cache_release(struct kmem_cache *s)
{
slab_kmem_cache_release(s);
}
#endif
static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work)
{
LIST_HEAD(to_destroy);
@ -418,11 +440,7 @@ static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work)
list_for_each_entry_safe(s, s2, &to_destroy, list) {
debugfs_slab_release(s);
kfence_shutdown_cache(s);
#ifdef SLAB_SUPPORTS_SYSFS
sysfs_slab_release(s);
#else
slab_kmem_cache_release(s);
#endif
kmem_cache_release(s);
}
}
@ -437,20 +455,11 @@ static int shutdown_cache(struct kmem_cache *s)
list_del(&s->list);
if (s->flags & SLAB_TYPESAFE_BY_RCU) {
#ifdef SLAB_SUPPORTS_SYSFS
sysfs_slab_unlink(s);
#endif
list_add_tail(&s->list, &slab_caches_to_rcu_destroy);
schedule_work(&slab_caches_to_rcu_destroy_work);
} else {
kfence_shutdown_cache(s);
debugfs_slab_release(s);
#ifdef SLAB_SUPPORTS_SYSFS
sysfs_slab_unlink(s);
sysfs_slab_release(s);
#else
slab_kmem_cache_release(s);
#endif
}
return 0;
@ -465,14 +474,16 @@ void slab_kmem_cache_release(struct kmem_cache *s)
void kmem_cache_destroy(struct kmem_cache *s)
{
int refcnt;
if (unlikely(!s) || !kasan_check_byte(s))
return;
cpus_read_lock();
mutex_lock(&slab_mutex);
s->refcount--;
if (s->refcount)
refcnt = --s->refcount;
if (refcnt)
goto out_unlock;
WARN(shutdown_cache(s),
@ -481,6 +492,8 @@ void kmem_cache_destroy(struct kmem_cache *s)
out_unlock:
mutex_unlock(&slab_mutex);
cpus_read_unlock();
if (!refcnt && !(s->flags & SLAB_TYPESAFE_BY_RCU))
kmem_cache_release(s);
}
EXPORT_SYMBOL(kmem_cache_destroy);