[PATCH v3 2/2] mm: avoid slub allocation while holding list_lock

[Yu Zhao]

If we are already under list_lock, don't call kmalloc(). Otherwise we
will run into deadlock because kmalloc() also tries to grab the same
lock.

Fixing the problem by using a static bitmap instead.

  WARNING: possible recursive locking detected
  --------------------------------------------
  mount-encrypted/4921 is trying to acquire lock:
  (&(&n->list_lock)->rlock){-.-.}, at: ___slab_alloc+0x104/0x437

  but task is already holding lock:
  (&(&n->list_lock)->rlock){-.-.}, at: __kmem_cache_shutdown+0x81/0x3cb

  other info that might help us debug this:
   Possible unsafe locking scenario:

         CPU0
         ----
    lock(&(&n->list_lock)->rlock);
    lock(&(&n->list_lock)->rlock);

   *** DEADLOCK ***

Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
---
 mm/slub.c | 88 +++++++++++++++++++++++++++++--------------------------
 1 file changed, 47 insertions(+), 41 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 445ef8b2aec0..c1de01730648 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -441,19 +441,38 @@ static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
 }
 
 #ifdef CONFIG_SLUB_DEBUG
+static unsigned long object_map[BITS_TO_LONGS(MAX_OBJS_PER_PAGE)];
+static DEFINE_SPINLOCK(object_map_lock);
+
 /*
  * Determine a map of object in use on a page.
  *
  * Node listlock must be held to guarantee that the page does
  * not vanish from under us.
  */
-static void get_map(struct kmem_cache *s, struct page *page, unsigned long *map)
+static unsigned long *get_map(struct kmem_cache *s, struct page *page)
 {
 	void *p;
 	void *addr = page_address(page);
 
+	VM_BUG_ON(!irqs_disabled());
+
+	spin_lock(&object_map_lock);
+
+	bitmap_zero(object_map, page->objects);
+
 	for (p = page->freelist; p; p = get_freepointer(s, p))
-		set_bit(slab_index(p, s, addr), map);
+		set_bit(slab_index(p, s, addr), object_map);
+
+	return object_map;
+}
+
+static void put_map(unsigned long *map)
+{
+	VM_BUG_ON(map != object_map);
+	lockdep_assert_held(&object_map_lock);
+
+	spin_unlock(&object_map_lock);
 }
 
 static inline unsigned int size_from_object(struct kmem_cache *s)
@@ -3683,13 +3702,12 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
 #ifdef CONFIG_SLUB_DEBUG
 	void *addr = page_address(page);
 	void *p;
-	unsigned long *map = bitmap_zalloc(page->objects, GFP_ATOMIC);
-	if (!map)
-		return;
+	unsigned long *map;
+
 	slab_err(s, page, text, s->name);
 	slab_lock(page);
 
-	get_map(s, page, map);
+	map = get_map(s, page);
 	for_each_object(p, s, addr, page->objects) {
 
 		if (!test_bit(slab_index(p, s, addr), map)) {
@@ -3697,8 +3715,9 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
 			print_tracking(s, p);
 		}
 	}
+	put_map(map);
+
 	slab_unlock(page);
-	bitmap_free(map);
 #endif
 }
 
@@ -4384,19 +4403,19 @@ static int count_total(struct page *page)
 #endif
 
 #ifdef CONFIG_SLUB_DEBUG
-static void validate_slab(struct kmem_cache *s, struct page *page,
-						unsigned long *map)
+static void validate_slab(struct kmem_cache *s, struct page *page)
 {
 	void *p;
 	void *addr = page_address(page);
+	unsigned long *map;
+
+	slab_lock(page);
 
 	if (!check_slab(s, page) || !on_freelist(s, page, NULL))
-		return;
+		goto unlock;
 
 	/* Now we know that a valid freelist exists */
-	bitmap_zero(map, page->objects);
-
-	get_map(s, page, map);
+	map = get_map(s, page);
 	for_each_object(p, s, addr, page->objects) {
 		u8 val = test_bit(slab_index(p, s, addr), map) ?
 			 SLUB_RED_INACTIVE : SLUB_RED_ACTIVE;
@@ -4404,18 +4423,13 @@ static void validate_slab(struct kmem_cache *s, struct page *page,
 		if (!check_object(s, page, p, val))
 			break;
 	}
-}
-
-static void validate_slab_slab(struct kmem_cache *s, struct page *page,
-						unsigned long *map)
-{
-	slab_lock(page);
-	validate_slab(s, page, map);
+	put_map(map);
+unlock:
 	slab_unlock(page);
 }
 
 static int validate_slab_node(struct kmem_cache *s,
-		struct kmem_cache_node *n, unsigned long *map)
+		struct kmem_cache_node *n)
 {
 	unsigned long count = 0;
 	struct page *page;
@@ -4424,7 +4438,7 @@ static int validate_slab_node(struct kmem_cache *s,
 	spin_lock_irqsave(&n->list_lock, flags);
 
 	list_for_each_entry(page, &n->partial, slab_list) {
-		validate_slab_slab(s, page, map);
+		validate_slab(s, page);
 		count++;
 	}
 	if (count != n->nr_partial)
@@ -4435,7 +4449,7 @@ static int validate_slab_node(struct kmem_cache *s,
 		goto out;
 
 	list_for_each_entry(page, &n->full, slab_list) {
-		validate_slab_slab(s, page, map);
+		validate_slab(s, page);
 		count++;
 	}
 	if (count != atomic_long_read(&n->nr_slabs))
@@ -4452,15 +4466,11 @@ static long validate_slab_cache(struct kmem_cache *s)
 	int node;
 	unsigned long count = 0;
 	struct kmem_cache_node *n;
-	unsigned long *map = bitmap_alloc(oo_objects(s->max), GFP_KERNEL);
-
-	if (!map)
-		return -ENOMEM;
 
 	flush_all(s);
 	for_each_kmem_cache_node(s, node, n)
-		count += validate_slab_node(s, n, map);
-	bitmap_free(map);
+		count += validate_slab_node(s, n);
+
 	return count;
 }
 /*
@@ -4590,18 +4600,17 @@ static int add_location(struct loc_track *t, struct kmem_cache *s,
 }
 
 static void process_slab(struct loc_track *t, struct kmem_cache *s,
-		struct page *page, enum track_item alloc,
-		unsigned long *map)
+		struct page *page, enum track_item alloc)
 {
 	void *addr = page_address(page);
 	void *p;
+	unsigned long *map;
 
-	bitmap_zero(map, page->objects);
-	get_map(s, page, map);
-
+	map = get_map(s, page);
 	for_each_object(p, s, addr, page->objects)
 		if (!test_bit(slab_index(p, s, addr), map))
 			add_location(t, s, get_track(s, p, alloc));
+	put_map(map);
 }
 
 static int list_locations(struct kmem_cache *s, char *buf,
@@ -4612,11 +4621,9 @@ static int list_locations(struct kmem_cache *s, char *buf,
 	struct loc_track t = { 0, 0, NULL };
 	int node;
 	struct kmem_cache_node *n;
-	unsigned long *map = bitmap_alloc(oo_objects(s->max), GFP_KERNEL);
 
-	if (!map || !alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
-				     GFP_KERNEL)) {
-		bitmap_free(map);
+	if (!alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
+			     GFP_KERNEL)) {
 		return sprintf(buf, "Out of memory\n");
 	}
 	/* Push back cpu slabs */
@@ -4631,9 +4638,9 @@ static int list_locations(struct kmem_cache *s, char *buf,
 
 		spin_lock_irqsave(&n->list_lock, flags);
 		list_for_each_entry(page, &n->partial, slab_list)
-			process_slab(&t, s, page, alloc, map);
+			process_slab(&t, s, page, alloc);
 		list_for_each_entry(page, &n->full, slab_list)
-			process_slab(&t, s, page, alloc, map);
+			process_slab(&t, s, page, alloc);
 		spin_unlock_irqrestore(&n->list_lock, flags);
 	}
 
@@ -4682,7 +4689,6 @@ static int list_locations(struct kmem_cache *s, char *buf,
 	}
 
 	free_loc_track(&t);
-	bitmap_free(map);
 	if (!t.count)
 		len += sprintf(buf, "No data\n");
 	return len;
-- 
2.23.0.237.gc6a4ce50a0-goog