Merge branch 'slab/for-6.1/slub_validation_locking' into slab/for-next

My series [1] to fix validation races for caches with enabled debugging.

By decoupling the debug cache operation more from non-debug fastpaths,
additional locking simplifications were possible and done afterwards.

Additional cleanup of PREEMPT_RT specific code on top, by Thomas Gleixner.

[1] https://lore.kernel.org/all/20220823170400.26546-1-vbabka@suse.cz/

mm/slub.c

@@ -50,7 +50,7 @@
  *   1. slab_mutex (Global Mutex)
  *   2. node->list_lock (Spinlock)
  *   3. kmem_cache->cpu_slab->lock (Local lock)
- *   4. slab_lock(slab) (Only on some arches or for debugging)
+ *   4. slab_lock(slab) (Only on some arches)
  *   5. object_map_lock (Only for debugging)
  *
  *   slab_mutex
@@ -64,8 +64,9 @@
  *   The slab_lock is a wrapper around the page lock, thus it is a bit
  *   spinlock.
  *
- *   The slab_lock is only used for debugging and on arches that do not
- *   have the ability to do a cmpxchg_double. It only protects:
+ *   The slab_lock is only used on arches that do not have the ability
+ *   to do a cmpxchg_double. It only protects:
+ *
  *	A. slab->freelist	-> List of free objects in a slab
  *	B. slab->inuse		-> Number of objects in use
  *	C. slab->objects	-> Number of objects in slab
@@ -94,15 +95,20 @@
  *   allocating a long series of objects that fill up slabs does not require
  *   the list lock.
  *
+ *   For debug caches, all allocations are forced to go through a list_lock
+ *   protected region to serialize against concurrent validation.
+ *
  *   cpu_slab->lock local lock
  *
  *   This locks protect slowpath manipulation of all kmem_cache_cpu fields
  *   except the stat counters. This is a percpu structure manipulated only by
  *   the local cpu, so the lock protects against being preempted or interrupted
  *   by an irq. Fast path operations rely on lockless operations instead.
- *   On PREEMPT_RT, the local lock does not actually disable irqs (and thus
- *   prevent the lockless operations), so fastpath operations also need to take
- *   the lock and are no longer lockless.
+ *
+ *   On PREEMPT_RT, the local lock neither disables interrupts nor preemption
+ *   which means the lockless fastpath cannot be used as it might interfere with
+ *   an in-progress slow path operations. In this case the local lock is always
+ *   taken but it still utilizes the freelist for the common operations.
  *
  *   lockless fastpaths
  *
@@ -163,8 +169,9 @@
  * function call even on !PREEMPT_RT, use inline preempt_disable() there.
  */
 #ifndef CONFIG_PREEMPT_RT
-#define slub_get_cpu_ptr(var)	get_cpu_ptr(var)
-#define slub_put_cpu_ptr(var)	put_cpu_ptr(var)
+#define slub_get_cpu_ptr(var)		get_cpu_ptr(var)
+#define slub_put_cpu_ptr(var)		put_cpu_ptr(var)
+#define USE_LOCKLESS_FAST_PATH()	(true)
 #else
 #define slub_get_cpu_ptr(var)		\
 ({					\
@@ -176,6 +183,7 @@ do {					\
 	(void)(var);			\
 	migrate_enable();		\
 } while (0)
+#define USE_LOCKLESS_FAST_PATH()	(false)
 #endif
 
 #ifdef CONFIG_SLUB_DEBUG
@@ -447,7 +455,7 @@ slub_set_cpu_partial(struct kmem_cache *s, unsigned int nr_objects)
 /*
  * Per slab locking using the pagelock
  */
-static __always_inline void __slab_lock(struct slab *slab)
+static __always_inline void slab_lock(struct slab *slab)
 {
 	struct page *page = slab_page(slab);
 
@@ -455,7 +463,7 @@ static __always_inline void __slab_lock(struct slab *slab)
 	bit_spin_lock(PG_locked, &page->flags);
 }
 
-static __always_inline void __slab_unlock(struct slab *slab)
+static __always_inline void slab_unlock(struct slab *slab)
 {
 	struct page *page = slab_page(slab);
 
@@ -463,31 +471,19 @@ static __always_inline void __slab_unlock(struct slab *slab)
 	__bit_spin_unlock(PG_locked, &page->flags);
 }
 
-static __always_inline void slab_lock(struct slab *slab, unsigned long *flags)
-{
-	if (IS_ENABLED(CONFIG_PREEMPT_RT))
-		local_irq_save(*flags);
-	__slab_lock(slab);
-}
-
-static __always_inline void slab_unlock(struct slab *slab, unsigned long *flags)
-{
-	__slab_unlock(slab);
-	if (IS_ENABLED(CONFIG_PREEMPT_RT))
-		local_irq_restore(*flags);
-}
-
 /*
  * Interrupts must be disabled (for the fallback code to work right), typically
- * by an _irqsave() lock variant. Except on PREEMPT_RT where locks are different
- * so we disable interrupts as part of slab_[un]lock().
+ * by an _irqsave() lock variant. On PREEMPT_RT the preempt_disable(), which is
+ * part of bit_spin_lock(), is sufficient because the policy is not to allow any
+ * allocation/ free operation in hardirq context. Therefore nothing can
+ * interrupt the operation.
  */
 static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct slab *slab,
 		void *freelist_old, unsigned long counters_old,
 		void *freelist_new, unsigned long counters_new,
 		const char *n)
 {
-	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+	if (USE_LOCKLESS_FAST_PATH())
 		lockdep_assert_irqs_disabled();
 #if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
     defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
@@ -499,18 +495,15 @@ static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct slab *slab
 	} else
 #endif
 	{
-		/* init to 0 to prevent spurious warnings */
-		unsigned long flags = 0;
-
-		slab_lock(slab, &flags);
+		slab_lock(slab);
 		if (slab->freelist == freelist_old &&
 					slab->counters == counters_old) {
 			slab->freelist = freelist_new;
 			slab->counters = counters_new;
-			slab_unlock(slab, &flags);
+			slab_unlock(slab);
 			return true;
 		}
-		slab_unlock(slab, &flags);
+		slab_unlock(slab);
 	}
 
 	cpu_relax();
@@ -541,16 +534,16 @@ static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct slab *slab,
 		unsigned long flags;
 
 		local_irq_save(flags);
-		__slab_lock(slab);
+		slab_lock(slab);
 		if (slab->freelist == freelist_old &&
 					slab->counters == counters_old) {
 			slab->freelist = freelist_new;
 			slab->counters = counters_new;
-			__slab_unlock(slab);
+			slab_unlock(slab);
 			local_irq_restore(flags);
 			return true;
 		}
-		__slab_unlock(slab);
+		slab_unlock(slab);
 		local_irq_restore(flags);
 	}
 
@@ -566,7 +559,7 @@ static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct slab *slab,
 
 #ifdef CONFIG_SLUB_DEBUG
 static unsigned long object_map[BITS_TO_LONGS(MAX_OBJS_PER_PAGE)];
-static DEFINE_RAW_SPINLOCK(object_map_lock);
+static DEFINE_SPINLOCK(object_map_lock);
 
 static void __fill_map(unsigned long *obj_map, struct kmem_cache *s,
 		       struct slab *slab)
@@ -600,30 +593,6 @@ static bool slab_add_kunit_errors(void)
 static inline bool slab_add_kunit_errors(void) { return false; }
 #endif
 
-/*
- * Determine a map of objects in use in a slab.
- *
- * Node listlock must be held to guarantee that the slab does
- * not vanish from under us.
- */
-static unsigned long *get_map(struct kmem_cache *s, struct slab *slab)
-	__acquires(&object_map_lock)
-{
-	VM_BUG_ON(!irqs_disabled());
-
-	raw_spin_lock(&object_map_lock);
-
-	__fill_map(object_map, s, slab);
-
-	return object_map;
-}
-
-static void put_map(unsigned long *map) __releases(&object_map_lock)
-{
-	VM_BUG_ON(map != object_map);
-	raw_spin_unlock(&object_map_lock);
-}
-
 static inline unsigned int size_from_object(struct kmem_cache *s)
 {
 	if (s->flags & SLAB_RED_ZONE)
@@ -1329,17 +1298,14 @@ static inline int alloc_consistency_checks(struct kmem_cache *s,
 }
 
 static noinline int alloc_debug_processing(struct kmem_cache *s,
-					struct slab *slab,
-					void *object, unsigned long addr)
+					struct slab *slab, void *object)
 {
 	if (s->flags & SLAB_CONSISTENCY_CHECKS) {
 		if (!alloc_consistency_checks(s, slab, object))
 			goto bad;
 	}
 
-	/* Success perform special debug activities for allocs */
-	if (s->flags & SLAB_STORE_USER)
-		set_track(s, object, TRACK_ALLOC, addr);
+	/* Success. Perform special debug activities for allocs */
 	trace(s, slab, object, 1);
 	init_object(s, object, SLUB_RED_ACTIVE);
 	return 1;
@@ -1390,63 +1356,6 @@ static inline int free_consistency_checks(struct kmem_cache *s,
 	return 1;
 }
 
-/* Supports checking bulk free of a constructed freelist */
-static noinline int free_debug_processing(
-	struct kmem_cache *s, struct slab *slab,
-	void *head, void *tail, int bulk_cnt,
-	unsigned long addr)
-{
-	struct kmem_cache_node *n = get_node(s, slab_nid(slab));
-	void *object = head;
-	int cnt = 0;
-	unsigned long flags, flags2;
-	int ret = 0;
-	depot_stack_handle_t handle = 0;
-
-	if (s->flags & SLAB_STORE_USER)
-		handle = set_track_prepare();
-
-	spin_lock_irqsave(&n->list_lock, flags);
-	slab_lock(slab, &flags2);
-
-	if (s->flags & SLAB_CONSISTENCY_CHECKS) {
-		if (!check_slab(s, slab))
-			goto out;
-	}
-
-next_object:
-	cnt++;
-
-	if (s->flags & SLAB_CONSISTENCY_CHECKS) {
-		if (!free_consistency_checks(s, slab, object, addr))
-			goto out;
-	}
-
-	if (s->flags & SLAB_STORE_USER)
-		set_track_update(s, object, TRACK_FREE, addr, handle);
-	trace(s, slab, object, 0);
-	/* Freepointer not overwritten by init_object(), SLAB_POISON moved it */
-	init_object(s, object, SLUB_RED_INACTIVE);
-
-	/* Reached end of constructed freelist yet? */
-	if (object != tail) {
-		object = get_freepointer(s, object);
-		goto next_object;
-	}
-	ret = 1;
-
-out:
-	if (cnt != bulk_cnt)
-		slab_err(s, slab, "Bulk freelist count(%d) invalid(%d)\n",
-			 bulk_cnt, cnt);
-
-	slab_unlock(slab, &flags2);
-	spin_unlock_irqrestore(&n->list_lock, flags);
-	if (!ret)
-		slab_fix(s, "Object at 0x%p not freed", object);
-	return ret;
-}
-
 /*
  * Parse a block of slub_debug options. Blocks are delimited by ';'
  *
@@ -1666,16 +1575,18 @@ static inline
 void setup_slab_debug(struct kmem_cache *s, struct slab *slab, void *addr) {}
 
 static inline int alloc_debug_processing(struct kmem_cache *s,
-	struct slab *slab, void *object, unsigned long addr) { return 0; }
+	struct slab *slab, void *object) { return 0; }
 
-static inline int free_debug_processing(
+static inline void free_debug_processing(
 	struct kmem_cache *s, struct slab *slab,
 	void *head, void *tail, int bulk_cnt,
-	unsigned long addr) { return 0; }
+	unsigned long addr) {}
 
 static inline void slab_pad_check(struct kmem_cache *s, struct slab *slab) {}
 static inline int check_object(struct kmem_cache *s, struct slab *slab,
 			void *object, u8 val) { return 1; }
+static inline void set_track(struct kmem_cache *s, void *object,
+			     enum track_item alloc, unsigned long addr) {}
 static inline void add_full(struct kmem_cache *s, struct kmem_cache_node *n,
 					struct slab *slab) {}
 static inline void remove_full(struct kmem_cache *s, struct kmem_cache_node *n,
@@ -1967,11 +1878,13 @@ static struct slab *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
 		 */
 		slab = alloc_slab_page(alloc_gfp, node, oo);
 		if (unlikely(!slab))
-			goto out;
+			return NULL;
 		stat(s, ORDER_FALLBACK);
 	}
 
 	slab->objects = oo_objects(oo);
+	slab->inuse = 0;
+	slab->frozen = 0;
 
 	account_slab(slab, oo_order(oo), s, flags);
 
@@ -1998,15 +1911,6 @@ static struct slab *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
 		set_freepointer(s, p, NULL);
 	}
 
-	slab->inuse = slab->objects;
-	slab->frozen = 1;
-
-out:
-	if (!slab)
-		return NULL;
-
-	inc_slabs_node(s, slab_nid(slab), slab->objects);
-
 	return slab;
 }
 
@@ -2093,6 +1997,75 @@ static inline void remove_partial(struct kmem_cache_node *n,
 	n->nr_partial--;
 }
 
+/*
+ * Called only for kmem_cache_debug() caches instead of acquire_slab(), with a
+ * slab from the n->partial list. Remove only a single object from the slab, do
+ * the alloc_debug_processing() checks and leave the slab on the list, or move
+ * it to full list if it was the last free object.
+ */
+static void *alloc_single_from_partial(struct kmem_cache *s,
+		struct kmem_cache_node *n, struct slab *slab)
+{
+	void *object;
+
+	lockdep_assert_held(&n->list_lock);
+
+	object = slab->freelist;
+	slab->freelist = get_freepointer(s, object);
+	slab->inuse++;
+
+	if (!alloc_debug_processing(s, slab, object)) {
+		remove_partial(n, slab);
+		return NULL;
+	}
+
+	if (slab->inuse == slab->objects) {
+		remove_partial(n, slab);
+		add_full(s, n, slab);
+	}
+
+	return object;
+}
+
+/*
+ * Called only for kmem_cache_debug() caches to allocate from a freshly
+ * allocated slab. Allocate a single object instead of whole freelist
+ * and put the slab to the partial (or full) list.
+ */
+static void *alloc_single_from_new_slab(struct kmem_cache *s,
+					struct slab *slab)
+{
+	int nid = slab_nid(slab);
+	struct kmem_cache_node *n = get_node(s, nid);
+	unsigned long flags;
+	void *object;
+
+
+	object = slab->freelist;
+	slab->freelist = get_freepointer(s, object);
+	slab->inuse = 1;
+
+	if (!alloc_debug_processing(s, slab, object))
+		/*
+		 * It's not really expected that this would fail on a
+		 * freshly allocated slab, but a concurrent memory
+		 * corruption in theory could cause that.
+		 */
+		return NULL;
+
+	spin_lock_irqsave(&n->list_lock, flags);
+
+	if (slab->inuse == slab->objects)
+		add_full(s, n, slab);
+	else
+		add_partial(n, slab, DEACTIVATE_TO_HEAD);
+
+	inc_slabs_node(s, nid, slab->objects);
+	spin_unlock_irqrestore(&n->list_lock, flags);
+
+	return object;
+}
+
 /*
  * Remove slab from the partial list, freeze it and
  * return the pointer to the freelist.
@@ -2173,6 +2146,13 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
 		if (!pfmemalloc_match(slab, gfpflags))
 			continue;
 
+		if (kmem_cache_debug(s)) {
+			object = alloc_single_from_partial(s, n, slab);
+			if (object)
+				break;
+			continue;
+		}
+
 		t = acquire_slab(s, n, slab, object == NULL);
 		if (!t)
 			break;
@@ -2779,6 +2759,110 @@ static inline unsigned long node_nr_objs(struct kmem_cache_node *n)
 {
 	return atomic_long_read(&n->total_objects);
 }
+
+/* Supports checking bulk free of a constructed freelist */
+static noinline void free_debug_processing(
+	struct kmem_cache *s, struct slab *slab,
+	void *head, void *tail, int bulk_cnt,
+	unsigned long addr)
+{
+	struct kmem_cache_node *n = get_node(s, slab_nid(slab));
+	struct slab *slab_free = NULL;
+	void *object = head;
+	int cnt = 0;
+	unsigned long flags;
+	bool checks_ok = false;
+	depot_stack_handle_t handle = 0;
+
+	if (s->flags & SLAB_STORE_USER)
+		handle = set_track_prepare();
+
+	spin_lock_irqsave(&n->list_lock, flags);
+
+	if (s->flags & SLAB_CONSISTENCY_CHECKS) {
+		if (!check_slab(s, slab))
+			goto out;
+	}
+
+	if (slab->inuse < bulk_cnt) {
+		slab_err(s, slab, "Slab has %d allocated objects but %d are to be freed\n",
+			 slab->inuse, bulk_cnt);
+		goto out;
+	}
+
+next_object:
+
+	if (++cnt > bulk_cnt)
+		goto out_cnt;
+
+	if (s->flags & SLAB_CONSISTENCY_CHECKS) {
+		if (!free_consistency_checks(s, slab, object, addr))
+			goto out;
+	}
+
+	if (s->flags & SLAB_STORE_USER)
+		set_track_update(s, object, TRACK_FREE, addr, handle);
+	trace(s, slab, object, 0);
+	/* Freepointer not overwritten by init_object(), SLAB_POISON moved it */
+	init_object(s, object, SLUB_RED_INACTIVE);
+
+	/* Reached end of constructed freelist yet? */
+	if (object != tail) {
+		object = get_freepointer(s, object);
+		goto next_object;
+	}
+	checks_ok = true;
+
+out_cnt:
+	if (cnt != bulk_cnt)
+		slab_err(s, slab, "Bulk free expected %d objects but found %d\n",
+			 bulk_cnt, cnt);
+
+out:
+	if (checks_ok) {
+		void *prior = slab->freelist;
+
+		/* Perform the actual freeing while we still hold the locks */
+		slab->inuse -= cnt;
+		set_freepointer(s, tail, prior);
+		slab->freelist = head;
+
+		/* Do we need to remove the slab from full or partial list? */
+		if (!prior) {
+			remove_full(s, n, slab);
+		} else if (slab->inuse == 0 &&
+			   n->nr_partial >= s->min_partial) {
+			remove_partial(n, slab);
+			stat(s, FREE_REMOVE_PARTIAL);
+		}
+
+		/* Do we need to discard the slab or add to partial list? */
+		if (slab->inuse == 0 && n->nr_partial >= s->min_partial) {
+			slab_free = slab;
+		} else if (!prior) {
+			add_partial(n, slab, DEACTIVATE_TO_TAIL);
+			stat(s, FREE_ADD_PARTIAL);
+		}
+	}
+
+	if (slab_free) {
+		/*
+		 * Update the counters while still holding n->list_lock to
+		 * prevent spurious validation warnings
+		 */
+		dec_slabs_node(s, slab_nid(slab_free), slab_free->objects);
+	}
+
+	spin_unlock_irqrestore(&n->list_lock, flags);
+
+	if (!checks_ok)
+		slab_fix(s, "Object at 0x%p not freed", object);
+
+	if (slab_free) {
+		stat(s, FREE_SLAB);
+		free_slab(s, slab_free);
+	}
+}
 #endif /* CONFIG_SLUB_DEBUG */
 
 #if defined(CONFIG_SLUB_DEBUG) || defined(CONFIG_SYSFS)
@@ -3027,36 +3111,52 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 		return NULL;
 	}
 
+	stat(s, ALLOC_SLAB);
+
+	if (kmem_cache_debug(s)) {
+		freelist = alloc_single_from_new_slab(s, slab);
+
+		if (unlikely(!freelist))
+			goto new_objects;
+
+		if (s->flags & SLAB_STORE_USER)
+			set_track(s, freelist, TRACK_ALLOC, addr);
+
+		return freelist;
+	}
+
 	/*
 	 * No other reference to the slab yet so we can
 	 * muck around with it freely without cmpxchg
 	 */
 	freelist = slab->freelist;
 	slab->freelist = NULL;
+	slab->inuse = slab->objects;
+	slab->frozen = 1;
 
-	stat(s, ALLOC_SLAB);
+	inc_slabs_node(s, slab_nid(slab), slab->objects);
 
 check_new_slab:
 
 	if (kmem_cache_debug(s)) {
-		if (!alloc_debug_processing(s, slab, freelist, addr)) {
-			/* Slab failed checks. Next slab needed */
-			goto new_slab;
-		} else {
-			/*
-			 * For debug case, we don't load freelist so that all
-			 * allocations go through alloc_debug_processing()
-			 */
-			goto return_single;
-		}
+		/*
+		 * For debug caches here we had to go through
+		 * alloc_single_from_partial() so just store the tracking info
+		 * and return the object
+		 */
+		if (s->flags & SLAB_STORE_USER)
+			set_track(s, freelist, TRACK_ALLOC, addr);
+		return freelist;
 	}
 
-	if (unlikely(!pfmemalloc_match(slab, gfpflags)))
+	if (unlikely(!pfmemalloc_match(slab, gfpflags))) {
 		/*
 		 * For !pfmemalloc_match() case we don't load freelist so that
 		 * we don't make further mismatched allocations easier.
 		 */
-		goto return_single;
+		deactivate_slab(s, slab, get_freepointer(s, freelist));
+		return freelist;
+	}
 
 retry_load_slab:
 
@@ -3080,11 +3180,6 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 	c->slab = slab;
 
 	goto load_freelist;
-
-return_single:
-
-	deactivate_slab(s, slab, get_freepointer(s, freelist));
-	return freelist;
 }
 
 /*
@@ -3188,14 +3283,8 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s, struct list_l
 
 	object = c->freelist;
 	slab = c->slab;
-	/*
-	 * We cannot use the lockless fastpath on PREEMPT_RT because if a
-	 * slowpath has taken the local_lock_irqsave(), it is not protected
-	 * against a fast path operation in an irq handler. So we need to take
-	 * the slow path which uses local_lock. It is still relatively fast if
-	 * there is a suitable cpu freelist.
-	 */
-	if (IS_ENABLED(CONFIG_PREEMPT_RT) ||
+
+	if (!USE_LOCKLESS_FAST_PATH() ||
 	    unlikely(!object || !slab || !node_match(slab, node))) {
 		object = __slab_alloc(s, gfpflags, node, addr, c);
 	} else {
@@ -3309,9 +3398,10 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
 	if (kfence_free(head))
 		return;
 
-	if (kmem_cache_debug(s) &&
-	    !free_debug_processing(s, slab, head, tail, cnt, addr))
+	if (kmem_cache_debug(s)) {
+		free_debug_processing(s, slab, head, tail, cnt, addr);
 		return;
+	}
 
 	do {
 		if (unlikely(n)) {
@@ -3431,6 +3521,7 @@ static __always_inline void do_slab_free(struct kmem_cache *s,
 	void *tail_obj = tail ? : head;
 	struct kmem_cache_cpu *c;
 	unsigned long tid;
+	void **freelist;
 
 redo:
 	/*
@@ -3445,9 +3536,13 @@ static __always_inline void do_slab_free(struct kmem_cache *s,
 	/* Same with comment on barrier() in slab_alloc_node() */
 	barrier();
 
-	if (likely(slab == c->slab)) {
-#ifndef CONFIG_PREEMPT_RT
-		void **freelist = READ_ONCE(c->freelist);
+	if (unlikely(slab != c->slab)) {
+		__slab_free(s, slab, head, tail_obj, cnt, addr);
+		return;
+	}
+
+	if (USE_LOCKLESS_FAST_PATH()) {
+		freelist = READ_ONCE(c->freelist);
 
 		set_freepointer(s, tail_obj, freelist);
 
@@ -3459,16 +3554,8 @@ static __always_inline void do_slab_free(struct kmem_cache *s,
 			note_cmpxchg_failure("slab_free", s, tid);
 			goto redo;
 		}
-#else /* CONFIG_PREEMPT_RT */
-		/*
-		 * We cannot use the lockless fastpath on PREEMPT_RT because if
-		 * a slowpath has taken the local_lock_irqsave(), it is not
-		 * protected against a fast path operation in an irq handler. So
-		 * we need to take the local_lock. We shouldn't simply defer to
-		 * __slab_free() as that wouldn't use the cpu freelist at all.
-		 */
-		void **freelist;
-
+	} else {
+		/* Update the free list under the local lock */
 		local_lock(&s->cpu_slab->lock);
 		c = this_cpu_ptr(s->cpu_slab);
 		if (unlikely(slab != c->slab)) {
@@ -3483,11 +3570,8 @@ static __always_inline void do_slab_free(struct kmem_cache *s,
 		c->tid = next_tid(tid);
 
 		local_unlock(&s->cpu_slab->lock);
-#endif
-		stat(s, FREE_FASTPATH);
-	} else
-		__slab_free(s, slab, head, tail_obj, cnt, addr);
-
+	}
+	stat(s, FREE_FASTPATH);
 }
 
 static __always_inline void slab_free(struct kmem_cache *s, struct slab *slab,
@@ -3896,6 +3980,7 @@ static void early_kmem_cache_node_alloc(int node)
 	slab = new_slab(kmem_cache_node, GFP_NOWAIT, node);
 
 	BUG_ON(!slab);
+	inc_slabs_node(kmem_cache_node, slab_nid(slab), slab->objects);
 	if (slab_nid(slab) != node) {
 		pr_err("SLUB: Unable to allocate memory from node %d\n", node);
 		pr_err("SLUB: Allocating a useless per node structure in order to be able to continue\n");
@@ -3910,7 +3995,6 @@ static void early_kmem_cache_node_alloc(int node)
 	n = kasan_slab_alloc(kmem_cache_node, n, GFP_KERNEL, false);
 	slab->freelist = get_freepointer(kmem_cache_node, n);
 	slab->inuse = 1;
-	slab->frozen = 0;
 	kmem_cache_node->node[node] = n;
 	init_kmem_cache_node(n);
 	inc_slabs_node(kmem_cache_node, node, slab->objects);
@@ -4197,23 +4281,21 @@ static void list_slab_objects(struct kmem_cache *s, struct slab *slab,
 {
 #ifdef CONFIG_SLUB_DEBUG
 	void *addr = slab_address(slab);
-	unsigned long flags;
-	unsigned long *map;
 	void *p;
 
 	slab_err(s, slab, text, s->name);
-	slab_lock(slab, &flags);
 
-	map = get_map(s, slab);
+	spin_lock(&object_map_lock);
+	__fill_map(object_map, s, slab);
+
 	for_each_object(p, s, addr, slab->objects) {
 
-		if (!test_bit(__obj_to_index(s, addr, p), map)) {
+		if (!test_bit(__obj_to_index(s, addr, p), object_map)) {
 			pr_err("Object 0x%p @offset=%tu\n", p, p - addr);
 			print_tracking(s, p);
 		}
 	}
-	put_map(map);
-	slab_unlock(slab, &flags);
+	spin_unlock(&object_map_lock);
 #endif
 }
 
@@ -4462,6 +4544,7 @@ static int __kmem_cache_do_shrink(struct kmem_cache *s)
 			if (free == slab->objects) {
 				list_move(&slab->slab_list, &discard);
 				n->nr_partial--;
+				dec_slabs_node(s, node, slab->objects);
 			} else if (free <= SHRINK_PROMOTE_MAX)
 				list_move(&slab->slab_list, promote + free - 1);
 		}
@@ -4477,7 +4560,7 @@ static int __kmem_cache_do_shrink(struct kmem_cache *s)
 
 		/* Release empty slabs */
 		list_for_each_entry_safe(slab, t, &discard, slab_list)
-			discard_slab(s, slab);
+			free_slab(s, slab);
 
 		if (slabs_node(s, node))
 			ret = 1;
@@ -4779,12 +4862,9 @@ static void validate_slab(struct kmem_cache *s, struct slab *slab,
 {
 	void *p;
 	void *addr = slab_address(slab);
-	unsigned long flags;
-
-	slab_lock(slab, &flags);
 
 	if (!check_slab(s, slab) || !on_freelist(s, slab, NULL))
-		goto unlock;
+		return;
 
 	/* Now we know that a valid freelist exists */
 	__fill_map(obj_map, s, slab);
@@ -4795,8 +4875,6 @@ static void validate_slab(struct kmem_cache *s, struct slab *slab,
 		if (!check_object(s, slab, p, val))
 			break;
 	}
-unlock:
-	slab_unlock(slab, &flags);
 }
 
 static int validate_slab_node(struct kmem_cache *s,
@@ -5400,7 +5478,7 @@ static ssize_t validate_store(struct kmem_cache *s,
 {
 	int ret = -EINVAL;
 
-	if (buf[0] == '1') {
+	if (buf[0] == '1' && kmem_cache_debug(s)) {
 		ret = validate_slab_cache(s);
 		if (ret >= 0)
 			ret = length;