mm/slub, kunit: Make slub_kunit unaffected by user specified flags

slub_kunit does not expect other debugging flags to be set when running
tests. When SLAB_RED_ZONE flag is set globally, test fails because the
flag affects number of errors reported.

To make slub_kunit unaffected by user specified debugging flags,
introduce SLAB_NO_USER_FLAGS to ignore them. With this flag, only flags
specified in the code are used and others are ignored.
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Link: https://lore.kernel.org/r/Yk0sY9yoJhFEXWOg@hyeyoo

include/linux/slab.h

@@ -112,6 +112,13 @@
 #define SLAB_KASAN		0
 #endif
 
+/*
+ * Ignore user specified debugging flags.
+ * Intended for caches created for self-tests so they have only flags
+ * specified in the code and other flags are ignored.
+ */
+#define SLAB_NO_USER_FLAGS	((slab_flags_t __force)0x10000000U)
+
 /* The following flags affect the page allocator grouping pages by mobility */
 /* Objects are reclaimable */
 #define SLAB_RECLAIM_ACCOUNT	((slab_flags_t __force)0x00020000U)

lib/slub_kunit.c

@@ -12,7 +12,7 @@ static int slab_errors;
 static void test_clobber_zone(struct kunit *test)
 {
 	struct kmem_cache *s = kmem_cache_create("TestSlub_RZ_alloc", 64, 0,
-				SLAB_RED_ZONE, NULL);
+				SLAB_RED_ZONE|SLAB_NO_USER_FLAGS, NULL);
 	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
 
 	kasan_disable_current();
@@ -30,7 +30,7 @@ static void test_clobber_zone(struct kunit *test)
 static void test_next_pointer(struct kunit *test)
 {
 	struct kmem_cache *s = kmem_cache_create("TestSlub_next_ptr_free", 64, 0,
-				SLAB_POISON, NULL);
+				SLAB_POISON|SLAB_NO_USER_FLAGS, NULL);
 	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
 	unsigned long tmp;
 	unsigned long *ptr_addr;
@@ -75,7 +75,7 @@ static void test_next_pointer(struct kunit *test)
 static void test_first_word(struct kunit *test)
 {
 	struct kmem_cache *s = kmem_cache_create("TestSlub_1th_word_free", 64, 0,
-				SLAB_POISON, NULL);
+				SLAB_POISON|SLAB_NO_USER_FLAGS, NULL);
 	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
 
 	kmem_cache_free(s, p);
@@ -90,7 +90,7 @@ static void test_first_word(struct kunit *test)
 static void test_clobber_50th_byte(struct kunit *test)
 {
 	struct kmem_cache *s = kmem_cache_create("TestSlub_50th_word_free", 64, 0,
-				SLAB_POISON, NULL);
+				SLAB_POISON|SLAB_NO_USER_FLAGS, NULL);
 	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
 
 	kmem_cache_free(s, p);
@@ -106,7 +106,7 @@ static void test_clobber_50th_byte(struct kunit *test)
 static void test_clobber_redzone_free(struct kunit *test)
 {
 	struct kmem_cache *s = kmem_cache_create("TestSlub_RZ_free", 64, 0,
-				SLAB_RED_ZONE, NULL);
+				SLAB_RED_ZONE|SLAB_NO_USER_FLAGS, NULL);
 	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
 
 	kasan_disable_current();

mm/slab.h

@@ -331,7 +331,7 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size,
 			  SLAB_ACCOUNT)
 #elif defined(CONFIG_SLUB)
 #define SLAB_CACHE_FLAGS (SLAB_NOLEAKTRACE | SLAB_RECLAIM_ACCOUNT | \
-			  SLAB_TEMPORARY | SLAB_ACCOUNT)
+			  SLAB_TEMPORARY | SLAB_ACCOUNT | SLAB_NO_USER_FLAGS)
 #else
 #define SLAB_CACHE_FLAGS (SLAB_NOLEAKTRACE)
 #endif
@@ -350,7 +350,8 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size,
 			      SLAB_NOLEAKTRACE | \
 			      SLAB_RECLAIM_ACCOUNT | \
 			      SLAB_TEMPORARY | \
-			      SLAB_ACCOUNT)
+			      SLAB_ACCOUNT | \
+			      SLAB_NO_USER_FLAGS)
 
 bool __kmem_cache_empty(struct kmem_cache *);
 int __kmem_cache_shutdown(struct kmem_cache *);

mm/slub.c

@@ -1584,6 +1584,9 @@ slab_flags_t kmem_cache_flags(unsigned int object_size,
 	slab_flags_t block_flags;
 	slab_flags_t slub_debug_local = slub_debug;
 
+	if (flags & SLAB_NO_USER_FLAGS)
+		return flags;
+
 	/*
 	 * If the slab cache is for debugging (e.g. kmemleak) then
 	 * don't store user (stack trace) information by default,