[PATCH v4 02/35] mm, slub: allocate private object map for debugfs listings

[Vlastimil Babka]

Slub has a static spinlock protected bitmap for marking which objects are on
freelist when it wants to list them, for situations where dynamically
allocating such map can lead to recursion or locking issues, and on-stack
bitmap would be too large.

The handlers of debugfs files alloc_traces and free_traces also currently use this
shared bitmap, but their syscall context makes it straightforward to allocate a
private map before entering locked sections, so switch these processing paths
to use a private bitmap.

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Christoph Lameter <cl@xxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
---
 mm/slub.c | 44 +++++++++++++++++++++++++++++---------------
 1 file changed, 29 insertions(+), 15 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index f5908e6b6fb1..211d380d94d1 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -454,6 +454,18 @@ static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
 static unsigned long object_map[BITS_TO_LONGS(MAX_OBJS_PER_PAGE)];
 static DEFINE_SPINLOCK(object_map_lock);
 
+static void __fill_map(unsigned long *obj_map, struct kmem_cache *s,
+		       struct page *page)
+{
+	void *addr = page_address(page);
+	void *p;
+
+	bitmap_zero(obj_map, page->objects);
+
+	for (p = page->freelist; p; p = get_freepointer(s, p))
+		set_bit(__obj_to_index(s, addr, p), obj_map);
+}
+
 #if IS_ENABLED(CONFIG_KUNIT)
 static bool slab_add_kunit_errors(void)
 {
@@ -483,17 +495,11 @@ static inline bool slab_add_kunit_errors(void) { return false; }
 static unsigned long *get_map(struct kmem_cache *s, struct page *page)
 	__acquires(&object_map_lock)
 {
-	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(__obj_to_index(s, addr, p), object_map);
+	__fill_map(object_map, s, page);
 
 	return object_map;
 }
@@ -4876,17 +4882,17 @@ 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)
+		struct page *page, enum track_item alloc,
+		unsigned long *obj_map)
 {
 	void *addr = page_address(page);
 	void *p;
-	unsigned long *map;
 
-	map = get_map(s, page);
+	__fill_map(obj_map, s, page);
+
 	for_each_object(p, s, addr, page->objects)
-		if (!test_bit(__obj_to_index(s, addr, p), map))
+		if (!test_bit(__obj_to_index(s, addr, p), obj_map))
 			add_location(t, s, get_track(s, p, alloc));
-	put_map(map);
 }
 #endif  /* CONFIG_DEBUG_FS   */
 #endif	/* CONFIG_SLUB_DEBUG */
@@ -5813,14 +5819,21 @@ static int slab_debug_trace_open(struct inode *inode, struct file *filep)
 	struct loc_track *t = __seq_open_private(filep, &slab_debugfs_sops,
 						sizeof(struct loc_track));
 	struct kmem_cache *s = file_inode(filep)->i_private;
+	unsigned long *obj_map;
+
+	obj_map = bitmap_alloc(oo_objects(s->oo), GFP_KERNEL);
+	if (!obj_map)
+		return -ENOMEM;
 
 	if (strcmp(filep->f_path.dentry->d_name.name, "alloc_traces") == 0)
 		alloc = TRACK_ALLOC;
 	else
 		alloc = TRACK_FREE;
 
-	if (!alloc_loc_track(t, PAGE_SIZE / sizeof(struct location), GFP_KERNEL))
+	if (!alloc_loc_track(t, PAGE_SIZE / sizeof(struct location), GFP_KERNEL)) {
+		bitmap_free(obj_map);
 		return -ENOMEM;
+	}
 
 	for_each_kmem_cache_node(s, node, n) {
 		unsigned long flags;
@@ -5831,12 +5844,13 @@ static int slab_debug_trace_open(struct inode *inode, struct file *filep)
 
 		spin_lock_irqsave(&n->list_lock, flags);
 		list_for_each_entry(page, &n->partial, slab_list)
-			process_slab(t, s, page, alloc);
+			process_slab(t, s, page, alloc, obj_map);
 		list_for_each_entry(page, &n->full, slab_list)
-			process_slab(t, s, page, alloc);
+			process_slab(t, s, page, alloc, obj_map);
 		spin_unlock_irqrestore(&n->list_lock, flags);
 	}
 
+	bitmap_free(obj_map);
 	return 0;
 }
 
-- 
2.32.0