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authorWaiman Long <longman@redhat.com>2022-08-12 21:30:33 +0300
committerVlastimil Babka <vbabka@suse.cz>2022-09-01 13:10:31 +0300
commit0495e337b7039191dfce6e03f5f830454b1fae6b (patch)
tree06272a39133e7954c4b90edf227703f7959aa1e6 /mm/slab_common.c
parent1c23f9e627a7b412978b4e852793c5e3c3efc555 (diff)
downloadlinux-0495e337b7039191dfce6e03f5f830454b1fae6b.tar.xz
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: 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>
Diffstat (limited to 'mm/slab_common.c')
-rw-r--r--mm/slab_common.c45
1 files changed, 29 insertions, 16 deletions
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 17996649cfe3..07b948288f84 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -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);