[PATCH v2 1/2] mm/slub, kunit: add SLAB_SKIP_KFENCE flag for cache creation

[Feng Tang]

When kfence is enabled, the buffer allocated from the test case
could be from a kfence pool, and the operation could be also
caught and reported by kfence first, causing the case to fail.

With default kfence setting, this is very difficult to be triggered.
By changing CONFIG_KFENCE_NUM_OBJECTS from 255 to 16383, and
CONFIG_KFENCE_SAMPLE_INTERVAL from 100 to 5, the allocation from
kfence did hit 7 times in different slub_kunit cases out of 900
times of boot test.

To avoid this, initially we tried is_kfence_address() to check this
and repeated allocation till finding a non-kfence address. Vlastimil
Babka suggested SLAB_SKIP_KFENCE flag could be used to achieve this
more simply.

Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
---
 lib/slub_kunit.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/lib/slub_kunit.c b/lib/slub_kunit.c
index 7a0564d7cb7a..a303adf8f11c 100644
--- a/lib/slub_kunit.c
+++ b/lib/slub_kunit.c
@@ -6,13 +6,15 @@
 #include <linux/kernel.h>
 #include "../mm/slab.h"
 
+#define DEFAULT_FLAGS	(SLAB_SKIP_KFENCE | SLAB_NO_USER_FLAGS)
+
 static struct kunit_resource resource;
 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|SLAB_NO_USER_FLAGS, NULL);
+				SLAB_RED_ZONE|DEFAULT_FLAGS, NULL);
 	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
 
 	kasan_disable_current();
@@ -30,7 +32,7 @@ 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|SLAB_NO_USER_FLAGS, NULL);
+				SLAB_POISON|DEFAULT_FLAGS, NULL);
 	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
 	unsigned long tmp;
 	unsigned long *ptr_addr;
@@ -75,7 +77,7 @@ 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|SLAB_NO_USER_FLAGS, NULL);
+				SLAB_POISON|DEFAULT_FLAGS, NULL);
 	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
 
 	kmem_cache_free(s, p);
@@ -90,7 +92,7 @@ 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|SLAB_NO_USER_FLAGS, NULL);
+				SLAB_POISON|DEFAULT_FLAGS, NULL);
 	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
 
 	kmem_cache_free(s, p);
@@ -106,7 +108,7 @@ 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|SLAB_NO_USER_FLAGS, NULL);
+				SLAB_RED_ZONE|DEFAULT_FLAGS, NULL);
 	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
 
 	kasan_disable_current();
-- 
2.34.1