kfence: make test case compatible with run time set sample interval

The parameter kfence_sample_interval can be set via boot parameter and
late shell command, which is convenient for automated tests and KFENCE
parameter optimization.  However, KFENCE test case just uses
compile-time CONFIG_KFENCE_SAMPLE_INTERVAL, which will make KFENCE test
case not run as users desired.  Export kfence_sample_interval, so that
KFENCE test case can use run-time-set sample interval.

Link: https://lkml.kernel.org/r/20220207034432.185532-1-liupeng256@huawei.com
Signed-off-by: Peng Liu <liupeng256@huawei.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Christian Knig <christian.koenig@amd.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/kfence.h

@@ -17,6 +17,8 @@
 #include <linux/atomic.h>
 #include <linux/static_key.h>
 
+extern unsigned long kfence_sample_interval;
+
 /*
  * We allocate an even number of pages, as it simplifies calculations to map
  * address to metadata indices; effectively, the very first page serves as an

mm/kfence/core.c

@@ -47,7 +47,8 @@
 
 static bool kfence_enabled __read_mostly;
 
-static unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL;
+unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL;
+EXPORT_SYMBOL_GPL(kfence_sample_interval); /* Export for test modules. */
 
 #ifdef MODULE_PARAM_PREFIX
 #undef MODULE_PARAM_PREFIX

mm/kfence/kfence_test.c

@@ -268,13 +268,13 @@ static void *test_alloc(struct kunit *test, size_t size, gfp_t gfp, enum allocat
 	 * 100x the sample interval should be more than enough to ensure we get
 	 * a KFENCE allocation eventually.
 	 */
-	timeout = jiffies + msecs_to_jiffies(100 * CONFIG_KFENCE_SAMPLE_INTERVAL);
+	timeout = jiffies + msecs_to_jiffies(100 * kfence_sample_interval);
 	/*
 	 * Especially for non-preemption kernels, ensure the allocation-gate
 	 * timer can catch up: after @resched_after, every failed allocation
 	 * attempt yields, to ensure the allocation-gate timer is scheduled.
 	 */
-	resched_after = jiffies + msecs_to_jiffies(CONFIG_KFENCE_SAMPLE_INTERVAL);
+	resched_after = jiffies + msecs_to_jiffies(kfence_sample_interval);
 	do {
 		if (test_cache)
 			alloc = kmem_cache_alloc(test_cache, gfp);
@@ -608,7 +608,7 @@ static void test_gfpzero(struct kunit *test)
 	int i;
 
 	/* Skip if we think it'd take too long. */
-	KFENCE_TEST_REQUIRES(test, CONFIG_KFENCE_SAMPLE_INTERVAL <= 100);
+	KFENCE_TEST_REQUIRES(test, kfence_sample_interval <= 100);
 
 	setup_test_cache(test, size, 0, NULL);
 	buf1 = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY);
@@ -739,7 +739,7 @@ static void test_memcache_alloc_bulk(struct kunit *test)
 	 * 100x the sample interval should be more than enough to ensure we get
 	 * a KFENCE allocation eventually.
 	 */
-	timeout = jiffies + msecs_to_jiffies(100 * CONFIG_KFENCE_SAMPLE_INTERVAL);
+	timeout = jiffies + msecs_to_jiffies(100 * kfence_sample_interval);
 	do {
 		void *objects[100];
 		int i, num = kmem_cache_alloc_bulk(test_cache, GFP_ATOMIC, ARRAY_SIZE(objects),