SLUB: accurately compare debug flags during slab cache merge

This was posted on Aug 28 and fixes an issue that could cause troubles
when slab caches >=128k are created.

http://marc.info/?l=linux-mm&m=118798149918424&w=2

Currently we simply add the debug flags unconditional when checking for a
matching slab.  This creates issues for sysfs processing when slabs exist
that are exempt from debugging due to their huge size or because only a
subset of slabs was selected for debugging.

We need to only add the flags if kmem_cache_open() would also add them.

Create a function to calculate the flags that would be set
if the cache would be opened and use that function to determine
the flags before looking for a compatible slab.

[akpm@linux-foundation.org: fixlets]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slub.c

@@ -986,7 +986,9 @@ out:
 
 __setup("slub_debug", setup_slub_debug);
 
-static void kmem_cache_open_debug_check(struct kmem_cache *s)
+static unsigned long kmem_cache_flags(unsigned long objsize,
+	unsigned long flags, const char *name,
+	void (*ctor)(void *, struct kmem_cache *, unsigned long))
 {
 	/*
 	 * The page->offset field is only 16 bit wide. This is an offset
@@ -1000,19 +1002,21 @@ static void kmem_cache_open_debug_check(struct kmem_cache *s)
 	 * Debugging or ctor may create a need to move the free
 	 * pointer. Fail if this happens.
 	 */
-	if (s->objsize >= 65535 * sizeof(void *)) {
-		BUG_ON(s->flags & (SLAB_RED_ZONE | SLAB_POISON |
+	if (objsize >= 65535 * sizeof(void *)) {
+		BUG_ON(flags & (SLAB_RED_ZONE | SLAB_POISON |
 				SLAB_STORE_USER | SLAB_DESTROY_BY_RCU));
-		BUG_ON(s->ctor);
-	}
-	else
+		BUG_ON(ctor);
+	} else {
 		/*
 		 * Enable debugging if selected on the kernel commandline.
 		 */
 		if (slub_debug && (!slub_debug_slabs ||
-		    strncmp(slub_debug_slabs, s->name,
+		    strncmp(slub_debug_slabs, name,
 		    	strlen(slub_debug_slabs)) == 0))
-				s->flags |= slub_debug;
+				flags |= slub_debug;
+	}
+
+	return flags;
 }
 #else
 static inline void setup_object_debug(struct kmem_cache *s,
@@ -1029,7 +1033,12 @@ static inline int slab_pad_check(struct kmem_cache *s, struct page *page)
 static inline int check_object(struct kmem_cache *s, struct page *page,
 			void *object, int active) { return 1; }
 static inline void add_full(struct kmem_cache_node *n, struct page *page) {}
-static inline void kmem_cache_open_debug_check(struct kmem_cache *s) {}
+static inline unsigned long kmem_cache_flags(unsigned long objsize,
+	unsigned long flags, const char *name,
+	void (*ctor)(void *, struct kmem_cache *, unsigned long))
+{
+	return flags;
+}
 #define slub_debug 0
 #endif
 /*
@@ -2088,9 +2097,8 @@ static int kmem_cache_open(struct kmem_cache *s, gfp_t gfpflags,
 	s->name = name;
 	s->ctor = ctor;
 	s->objsize = size;
-	s->flags = flags;
 	s->align = align;
-	kmem_cache_open_debug_check(s);
+	s->flags = kmem_cache_flags(size, flags, name, ctor);
 
 	if (!calculate_sizes(s))
 		goto error;
@@ -2660,7 +2668,7 @@ static int slab_unmergeable(struct kmem_cache *s)
 }
 
 static struct kmem_cache *find_mergeable(size_t size,
-		size_t align, unsigned long flags,
+		size_t align, unsigned long flags, const char *name,
 		void (*ctor)(void *, struct kmem_cache *, unsigned long))
 {
 	struct kmem_cache *s;
@@ -2674,6 +2682,7 @@ static struct kmem_cache *find_mergeable(size_t size,
 	size = ALIGN(size, sizeof(void *));
 	align = calculate_alignment(flags, align, size);
 	size = ALIGN(size, align);
+	flags = kmem_cache_flags(size, flags, name, NULL);
 
 	list_for_each_entry(s, &slab_caches, list) {
 		if (slab_unmergeable(s))
@@ -2682,8 +2691,7 @@ static struct kmem_cache *find_mergeable(size_t size,
 		if (size > s->size)
 			continue;
 
-		if (((flags | slub_debug) & SLUB_MERGE_SAME) !=
-			(s->flags & SLUB_MERGE_SAME))
+		if ((flags & SLUB_MERGE_SAME) != (s->flags & SLUB_MERGE_SAME))
 				continue;
 		/*
 		 * Check if alignment is compatible.
@@ -2707,7 +2715,7 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 	struct kmem_cache *s;
 
 	down_write(&slub_lock);
-	s = find_mergeable(size, align, flags, ctor);
+	s = find_mergeable(size, align, flags, name, ctor);
 	if (s) {
 		s->refcount++;
 		/*