slub: remove kmalloc under list_lock from list_slab_objects() V2

list_slab_objects() is called when a slab is destroyed and there are
objects still left to list the objects in the syslog.  This is a pretty
rare event.

And there it seems we take the list_lock and call kmalloc while holding
that lock.

Perform the allocation in free_partial() before the list_lock is taken.

Fixes: bbd7d57b ("slub: Potential stack overflow")
Signed-off-by: Christopher Lameter <cl@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Yu Zhao <yuzhao@google.com>
Link: http://lkml.kernel.org/r/alpine.DEB.2.21.2002031721250.1668@www.lameter.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slub.c

@@ -3766,12 +3766,14 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
 }
 
 static void list_slab_objects(struct kmem_cache *s, struct page *page,
-							const char *text)
+			      const char *text, unsigned long *map)
 {
 #ifdef CONFIG_SLUB_DEBUG
 	void *addr = page_address(page);
 	void *p;
-	unsigned long *map;
+
+	if (!map)
+		return;
 
 	slab_err(s, page, text, s->name);
 	slab_lock(page);
@@ -3784,8 +3786,6 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
 			print_tracking(s, p);
 		}
 	}
-	put_map(map);
-
 	slab_unlock(page);
 #endif
 }
@@ -3799,6 +3799,11 @@ static void free_partial(struct kmem_cache *s, struct kmem_cache_node *n)
 {
 	LIST_HEAD(discard);
 	struct page *page, *h;
+	unsigned long *map = NULL;
+
+#ifdef CONFIG_SLUB_DEBUG
+	map = bitmap_alloc(oo_objects(s->max), GFP_KERNEL);
+#endif
 
 	BUG_ON(irqs_disabled());
 	spin_lock_irq(&n->list_lock);
@@ -3808,11 +3813,16 @@ static void free_partial(struct kmem_cache *s, struct kmem_cache_node *n)
 			list_add(&page->slab_list, &discard);
 		} else {
 			list_slab_objects(s, page,
-			"Objects remaining in %s on __kmem_cache_shutdown()");
+			  "Objects remaining in %s on __kmem_cache_shutdown()",
+			  map);
 		}
 	}
 	spin_unlock_irq(&n->list_lock);
 
+#ifdef CONFIG_SLUB_DEBUG
+	bitmap_free(map);
+#endif
+
 	list_for_each_entry_safe(page, h, &discard, slab_list)
 		discard_slab(s, page);
 }