kcsan: test: Add test cases for memory barrier instrumentation

Adds test cases to check that memory barriers are instrumented
correctly, and detection of missing memory barriers is working as
intended if CONFIG_KCSAN_STRICT=y.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/kcsan/kcsan_test.c b/kernel/kcsan/kcsan_test.c
index ec05487..5bf9455 100644 (file)
--- a/kernel/kcsan/kcsan_test.c
+++ b/kernel/kcsan/kcsan_test.c
@@ -16,9 +16,12 @@
 #define pr_fmt(fmt) "kcsan_test: " fmt
 
 #include <kunit/test.h>
+#include <linux/atomic.h>
+#include <linux/bitops.h>
 #include <linux/jiffies.h>
 #include <linux/kcsan-checks.h>
 #include <linux/kernel.h>
+#include <linux/mutex.h>
 #include <linux/sched.h>
 #include <linux/seqlock.h>
 #include <linux/spinlock.h>
@@ -305,6 +308,16 @@ static DEFINE_SEQLOCK(test_seqlock);
 __no_kcsan
 static noinline void sink_value(long v) { WRITE_ONCE(test_sink, v); }
 
+/*
+ * Generates a delay and some accesses that enter the runtime but do not produce
+ * data races.
+ */
+static noinline void test_delay(int iter)
+{
+       while (iter--)
+               sink_value(READ_ONCE(test_sink));
+}
+
 static noinline void test_kernel_read(void) { sink_value(test_var); }
 
 static noinline void test_kernel_write(void)
@@ -466,8 +479,219 @@ static noinline void test_kernel_xor_1bit(void)
        kcsan_nestable_atomic_end();
 }
 
+#define TEST_KERNEL_LOCKED(name, acquire, release)             \
+       static noinline void test_kernel_##name(void)           \
+       {                                                       \
+               long *flag = &test_struct.val[0];               \
+               long v = 0;                                     \
+               if (!(acquire))                                 \
+                       return;                                 \
+               while (v++ < 100) {                             \
+                       test_var++;                             \
+                       barrier();                              \
+               }                                               \
+               release;                                        \
+               test_delay(10);                                 \
+       }
+
+TEST_KERNEL_LOCKED(with_memorder,
+                  cmpxchg_acquire(flag, 0, 1) == 0,
+                  smp_store_release(flag, 0));
+TEST_KERNEL_LOCKED(wrong_memorder,
+                  cmpxchg_relaxed(flag, 0, 1) == 0,
+                  WRITE_ONCE(*flag, 0));
+TEST_KERNEL_LOCKED(atomic_builtin_with_memorder,
+                  __atomic_compare_exchange_n(flag, &v, 1, 0, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED),
+                  __atomic_store_n(flag, 0, __ATOMIC_RELEASE));
+TEST_KERNEL_LOCKED(atomic_builtin_wrong_memorder,
+                  __atomic_compare_exchange_n(flag, &v, 1, 0, __ATOMIC_RELAXED, __ATOMIC_RELAXED),
+                  __atomic_store_n(flag, 0, __ATOMIC_RELAXED));
+
 /* ===== Test cases ===== */
 
+/*
+ * Tests that various barriers have the expected effect on internal state. Not
+ * exhaustive on atomic_t operations. Unlike the selftest, also checks for
+ * too-strict barrier instrumentation; these can be tolerated, because it does
+ * not cause false positives, but at least we should be aware of such cases.
+ */
+static void test_barrier_nothreads(struct kunit *test)
+{
+#ifdef CONFIG_KCSAN_WEAK_MEMORY
+       struct kcsan_scoped_access *reorder_access = &current->kcsan_ctx.reorder_access;
+#else
+       struct kcsan_scoped_access *reorder_access = NULL;
+#endif
+       arch_spinlock_t arch_spinlock = __ARCH_SPIN_LOCK_UNLOCKED;
+       DEFINE_SPINLOCK(spinlock);
+       DEFINE_MUTEX(mutex);
+       atomic_t dummy;
+
+       KCSAN_TEST_REQUIRES(test, reorder_access != NULL);
+       KCSAN_TEST_REQUIRES(test, IS_ENABLED(CONFIG_SMP));
+
+#define __KCSAN_EXPECT_BARRIER(access_type, barrier, order_before, name)                       \
+       do {                                                                                    \
+               reorder_access->type = (access_type) | KCSAN_ACCESS_SCOPED;                     \
+               reorder_access->size = sizeof(test_var);                                        \
+               barrier;                                                                        \
+               KUNIT_EXPECT_EQ_MSG(test, reorder_access->size,                                 \
+                                   order_before ? 0 : sizeof(test_var),                        \
+                                   "improperly instrumented type=(" #access_type "): " name);  \
+       } while (0)
+#define KCSAN_EXPECT_READ_BARRIER(b, o)  __KCSAN_EXPECT_BARRIER(0, b, o, #b)
+#define KCSAN_EXPECT_WRITE_BARRIER(b, o) __KCSAN_EXPECT_BARRIER(KCSAN_ACCESS_WRITE, b, o, #b)
+#define KCSAN_EXPECT_RW_BARRIER(b, o)    __KCSAN_EXPECT_BARRIER(KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE, b, o, #b)
+
+       /* Force creating a valid entry in reorder_access first. */
+       test_var = 0;
+       while (test_var++ < 1000000 && reorder_access->size != sizeof(test_var))
+               __kcsan_check_read(&test_var, sizeof(test_var));
+       KUNIT_ASSERT_EQ(test, reorder_access->size, sizeof(test_var));
+
+       kcsan_nestable_atomic_begin(); /* No watchpoints in called functions. */
+
+       KCSAN_EXPECT_READ_BARRIER(mb(), true);
+       KCSAN_EXPECT_READ_BARRIER(wmb(), false);
+       KCSAN_EXPECT_READ_BARRIER(rmb(), true);
+       KCSAN_EXPECT_READ_BARRIER(smp_mb(), true);
+       KCSAN_EXPECT_READ_BARRIER(smp_wmb(), false);
+       KCSAN_EXPECT_READ_BARRIER(smp_rmb(), true);
+       KCSAN_EXPECT_READ_BARRIER(dma_wmb(), false);
+       KCSAN_EXPECT_READ_BARRIER(dma_rmb(), true);
+       KCSAN_EXPECT_READ_BARRIER(smp_mb__before_atomic(), true);
+       KCSAN_EXPECT_READ_BARRIER(smp_mb__after_atomic(), true);
+       KCSAN_EXPECT_READ_BARRIER(smp_mb__after_spinlock(), true);
+       KCSAN_EXPECT_READ_BARRIER(smp_store_mb(test_var, 0), true);
+       KCSAN_EXPECT_READ_BARRIER(smp_load_acquire(&test_var), false);
+       KCSAN_EXPECT_READ_BARRIER(smp_store_release(&test_var, 0), true);
+       KCSAN_EXPECT_READ_BARRIER(xchg(&test_var, 0), true);
+       KCSAN_EXPECT_READ_BARRIER(xchg_release(&test_var, 0), true);
+       KCSAN_EXPECT_READ_BARRIER(xchg_relaxed(&test_var, 0), false);
+       KCSAN_EXPECT_READ_BARRIER(cmpxchg(&test_var, 0,  0), true);
+       KCSAN_EXPECT_READ_BARRIER(cmpxchg_release(&test_var, 0,  0), true);
+       KCSAN_EXPECT_READ_BARRIER(cmpxchg_relaxed(&test_var, 0,  0), false);
+       KCSAN_EXPECT_READ_BARRIER(atomic_read(&dummy), false);
+       KCSAN_EXPECT_READ_BARRIER(atomic_read_acquire(&dummy), false);
+       KCSAN_EXPECT_READ_BARRIER(atomic_set(&dummy, 0), false);
+       KCSAN_EXPECT_READ_BARRIER(atomic_set_release(&dummy, 0), true);
+       KCSAN_EXPECT_READ_BARRIER(atomic_add(1, &dummy), false);
+       KCSAN_EXPECT_READ_BARRIER(atomic_add_return(1, &dummy), true);
+       KCSAN_EXPECT_READ_BARRIER(atomic_add_return_acquire(1, &dummy), false);
+       KCSAN_EXPECT_READ_BARRIER(atomic_add_return_release(1, &dummy), true);
+       KCSAN_EXPECT_READ_BARRIER(atomic_add_return_relaxed(1, &dummy), false);
+       KCSAN_EXPECT_READ_BARRIER(atomic_fetch_add(1, &dummy), true);
+       KCSAN_EXPECT_READ_BARRIER(atomic_fetch_add_acquire(1, &dummy), false);
+       KCSAN_EXPECT_READ_BARRIER(atomic_fetch_add_release(1, &dummy), true);
+       KCSAN_EXPECT_READ_BARRIER(atomic_fetch_add_relaxed(1, &dummy), false);
+       KCSAN_EXPECT_READ_BARRIER(test_and_set_bit(0, &test_var), true);
+       KCSAN_EXPECT_READ_BARRIER(test_and_clear_bit(0, &test_var), true);
+       KCSAN_EXPECT_READ_BARRIER(test_and_change_bit(0, &test_var), true);
+       KCSAN_EXPECT_READ_BARRIER(clear_bit_unlock(0, &test_var), true);
+       KCSAN_EXPECT_READ_BARRIER(__clear_bit_unlock(0, &test_var), true);
+       KCSAN_EXPECT_READ_BARRIER(clear_bit_unlock_is_negative_byte(0, &test_var), true);
+       KCSAN_EXPECT_READ_BARRIER(arch_spin_lock(&arch_spinlock), false);
+       KCSAN_EXPECT_READ_BARRIER(arch_spin_unlock(&arch_spinlock), true);
+       KCSAN_EXPECT_READ_BARRIER(spin_lock(&spinlock), false);
+       KCSAN_EXPECT_READ_BARRIER(spin_unlock(&spinlock), true);
+       KCSAN_EXPECT_READ_BARRIER(mutex_lock(&mutex), false);
+       KCSAN_EXPECT_READ_BARRIER(mutex_unlock(&mutex), true);
+
+       KCSAN_EXPECT_WRITE_BARRIER(mb(), true);
+       KCSAN_EXPECT_WRITE_BARRIER(wmb(), true);
+       KCSAN_EXPECT_WRITE_BARRIER(rmb(), false);
+       KCSAN_EXPECT_WRITE_BARRIER(smp_mb(), true);
+       KCSAN_EXPECT_WRITE_BARRIER(smp_wmb(), true);
+       KCSAN_EXPECT_WRITE_BARRIER(smp_rmb(), false);
+       KCSAN_EXPECT_WRITE_BARRIER(dma_wmb(), true);
+       KCSAN_EXPECT_WRITE_BARRIER(dma_rmb(), false);
+       KCSAN_EXPECT_WRITE_BARRIER(smp_mb__before_atomic(), true);
+       KCSAN_EXPECT_WRITE_BARRIER(smp_mb__after_atomic(), true);
+       KCSAN_EXPECT_WRITE_BARRIER(smp_mb__after_spinlock(), true);
+       KCSAN_EXPECT_WRITE_BARRIER(smp_store_mb(test_var, 0), true);
+       KCSAN_EXPECT_WRITE_BARRIER(smp_load_acquire(&test_var), false);
+       KCSAN_EXPECT_WRITE_BARRIER(smp_store_release(&test_var, 0), true);
+       KCSAN_EXPECT_WRITE_BARRIER(xchg(&test_var, 0), true);
+       KCSAN_EXPECT_WRITE_BARRIER(xchg_release(&test_var, 0), true);
+       KCSAN_EXPECT_WRITE_BARRIER(xchg_relaxed(&test_var, 0), false);
+       KCSAN_EXPECT_WRITE_BARRIER(cmpxchg(&test_var, 0,  0), true);
+       KCSAN_EXPECT_WRITE_BARRIER(cmpxchg_release(&test_var, 0,  0), true);
+       KCSAN_EXPECT_WRITE_BARRIER(cmpxchg_relaxed(&test_var, 0,  0), false);
+       KCSAN_EXPECT_WRITE_BARRIER(atomic_read(&dummy), false);
+       KCSAN_EXPECT_WRITE_BARRIER(atomic_read_acquire(&dummy), false);
+       KCSAN_EXPECT_WRITE_BARRIER(atomic_set(&dummy, 0), false);
+       KCSAN_EXPECT_WRITE_BARRIER(atomic_set_release(&dummy, 0), true);
+       KCSAN_EXPECT_WRITE_BARRIER(atomic_add(1, &dummy), false);
+       KCSAN_EXPECT_WRITE_BARRIER(atomic_add_return(1, &dummy), true);
+       KCSAN_EXPECT_WRITE_BARRIER(atomic_add_return_acquire(1, &dummy), false);
+       KCSAN_EXPECT_WRITE_BARRIER(atomic_add_return_release(1, &dummy), true);
+       KCSAN_EXPECT_WRITE_BARRIER(atomic_add_return_relaxed(1, &dummy), false);
+       KCSAN_EXPECT_WRITE_BARRIER(atomic_fetch_add(1, &dummy), true);
+       KCSAN_EXPECT_WRITE_BARRIER(atomic_fetch_add_acquire(1, &dummy), false);
+       KCSAN_EXPECT_WRITE_BARRIER(atomic_fetch_add_release(1, &dummy), true);
+       KCSAN_EXPECT_WRITE_BARRIER(atomic_fetch_add_relaxed(1, &dummy), false);
+       KCSAN_EXPECT_WRITE_BARRIER(test_and_set_bit(0, &test_var), true);
+       KCSAN_EXPECT_WRITE_BARRIER(test_and_clear_bit(0, &test_var), true);
+       KCSAN_EXPECT_WRITE_BARRIER(test_and_change_bit(0, &test_var), true);
+       KCSAN_EXPECT_WRITE_BARRIER(clear_bit_unlock(0, &test_var), true);
+       KCSAN_EXPECT_WRITE_BARRIER(__clear_bit_unlock(0, &test_var), true);
+       KCSAN_EXPECT_WRITE_BARRIER(clear_bit_unlock_is_negative_byte(0, &test_var), true);
+       KCSAN_EXPECT_WRITE_BARRIER(arch_spin_lock(&arch_spinlock), false);
+       KCSAN_EXPECT_WRITE_BARRIER(arch_spin_unlock(&arch_spinlock), true);
+       KCSAN_EXPECT_WRITE_BARRIER(spin_lock(&spinlock), false);
+       KCSAN_EXPECT_WRITE_BARRIER(spin_unlock(&spinlock), true);
+       KCSAN_EXPECT_WRITE_BARRIER(mutex_lock(&mutex), false);
+       KCSAN_EXPECT_WRITE_BARRIER(mutex_unlock(&mutex), true);
+
+       KCSAN_EXPECT_RW_BARRIER(mb(), true);
+       KCSAN_EXPECT_RW_BARRIER(wmb(), true);
+       KCSAN_EXPECT_RW_BARRIER(rmb(), true);
+       KCSAN_EXPECT_RW_BARRIER(smp_mb(), true);
+       KCSAN_EXPECT_RW_BARRIER(smp_wmb(), true);
+       KCSAN_EXPECT_RW_BARRIER(smp_rmb(), true);
+       KCSAN_EXPECT_RW_BARRIER(dma_wmb(), true);
+       KCSAN_EXPECT_RW_BARRIER(dma_rmb(), true);
+       KCSAN_EXPECT_RW_BARRIER(smp_mb__before_atomic(), true);
+       KCSAN_EXPECT_RW_BARRIER(smp_mb__after_atomic(), true);
+       KCSAN_EXPECT_RW_BARRIER(smp_mb__after_spinlock(), true);
+       KCSAN_EXPECT_RW_BARRIER(smp_store_mb(test_var, 0), true);
+       KCSAN_EXPECT_RW_BARRIER(smp_load_acquire(&test_var), false);
+       KCSAN_EXPECT_RW_BARRIER(smp_store_release(&test_var, 0), true);
+       KCSAN_EXPECT_RW_BARRIER(xchg(&test_var, 0), true);
+       KCSAN_EXPECT_RW_BARRIER(xchg_release(&test_var, 0), true);
+       KCSAN_EXPECT_RW_BARRIER(xchg_relaxed(&test_var, 0), false);
+       KCSAN_EXPECT_RW_BARRIER(cmpxchg(&test_var, 0,  0), true);
+       KCSAN_EXPECT_RW_BARRIER(cmpxchg_release(&test_var, 0,  0), true);
+       KCSAN_EXPECT_RW_BARRIER(cmpxchg_relaxed(&test_var, 0,  0), false);
+       KCSAN_EXPECT_RW_BARRIER(atomic_read(&dummy), false);
+       KCSAN_EXPECT_RW_BARRIER(atomic_read_acquire(&dummy), false);
+       KCSAN_EXPECT_RW_BARRIER(atomic_set(&dummy, 0), false);
+       KCSAN_EXPECT_RW_BARRIER(atomic_set_release(&dummy, 0), true);
+       KCSAN_EXPECT_RW_BARRIER(atomic_add(1, &dummy), false);
+       KCSAN_EXPECT_RW_BARRIER(atomic_add_return(1, &dummy), true);
+       KCSAN_EXPECT_RW_BARRIER(atomic_add_return_acquire(1, &dummy), false);
+       KCSAN_EXPECT_RW_BARRIER(atomic_add_return_release(1, &dummy), true);
+       KCSAN_EXPECT_RW_BARRIER(atomic_add_return_relaxed(1, &dummy), false);
+       KCSAN_EXPECT_RW_BARRIER(atomic_fetch_add(1, &dummy), true);
+       KCSAN_EXPECT_RW_BARRIER(atomic_fetch_add_acquire(1, &dummy), false);
+       KCSAN_EXPECT_RW_BARRIER(atomic_fetch_add_release(1, &dummy), true);
+       KCSAN_EXPECT_RW_BARRIER(atomic_fetch_add_relaxed(1, &dummy), false);
+       KCSAN_EXPECT_RW_BARRIER(test_and_set_bit(0, &test_var), true);
+       KCSAN_EXPECT_RW_BARRIER(test_and_clear_bit(0, &test_var), true);
+       KCSAN_EXPECT_RW_BARRIER(test_and_change_bit(0, &test_var), true);
+       KCSAN_EXPECT_RW_BARRIER(clear_bit_unlock(0, &test_var), true);
+       KCSAN_EXPECT_RW_BARRIER(__clear_bit_unlock(0, &test_var), true);
+       KCSAN_EXPECT_RW_BARRIER(clear_bit_unlock_is_negative_byte(0, &test_var), true);
+       KCSAN_EXPECT_RW_BARRIER(arch_spin_lock(&arch_spinlock), false);
+       KCSAN_EXPECT_RW_BARRIER(arch_spin_unlock(&arch_spinlock), true);
+       KCSAN_EXPECT_RW_BARRIER(spin_lock(&spinlock), false);
+       KCSAN_EXPECT_RW_BARRIER(spin_unlock(&spinlock), true);
+       KCSAN_EXPECT_RW_BARRIER(mutex_lock(&mutex), false);
+       KCSAN_EXPECT_RW_BARRIER(mutex_unlock(&mutex), true);
+
+       kcsan_nestable_atomic_end();
+}
+
 /* Simple test with normal data race. */
 __no_kcsan
 static void test_basic(struct kunit *test)
@@ -1039,6 +1263,90 @@ static void test_1bit_value_change(struct kunit *test)
                KUNIT_EXPECT_TRUE(test, match);
 }
 
+__no_kcsan
+static void test_correct_barrier(struct kunit *test)
+{
+       struct expect_report expect = {
+               .access = {
+                       { test_kernel_with_memorder, &test_var, sizeof(test_var), __KCSAN_ACCESS_RW(KCSAN_ACCESS_WRITE) },
+                       { test_kernel_with_memorder, &test_var, sizeof(test_var), __KCSAN_ACCESS_RW(0) },
+               },
+       };
+       bool match_expect = false;
+
+       test_struct.val[0] = 0; /* init unlocked */
+       begin_test_checks(test_kernel_with_memorder, test_kernel_with_memorder);
+       do {
+               match_expect = report_matches_any_reordered(&expect);
+       } while (!end_test_checks(match_expect));
+       KUNIT_EXPECT_FALSE(test, match_expect);
+}
+
+__no_kcsan
+static void test_missing_barrier(struct kunit *test)
+{
+       struct expect_report expect = {
+               .access = {
+                       { test_kernel_wrong_memorder, &test_var, sizeof(test_var), __KCSAN_ACCESS_RW(KCSAN_ACCESS_WRITE) },
+                       { test_kernel_wrong_memorder, &test_var, sizeof(test_var), __KCSAN_ACCESS_RW(0) },
+               },
+       };
+       bool match_expect = false;
+
+       test_struct.val[0] = 0; /* init unlocked */
+       begin_test_checks(test_kernel_wrong_memorder, test_kernel_wrong_memorder);
+       do {
+               match_expect = report_matches_any_reordered(&expect);
+       } while (!end_test_checks(match_expect));
+       if (IS_ENABLED(CONFIG_KCSAN_WEAK_MEMORY))
+               KUNIT_EXPECT_TRUE(test, match_expect);
+       else
+               KUNIT_EXPECT_FALSE(test, match_expect);
+}
+
+__no_kcsan
+static void test_atomic_builtins_correct_barrier(struct kunit *test)
+{
+       struct expect_report expect = {
+               .access = {
+                       { test_kernel_atomic_builtin_with_memorder, &test_var, sizeof(test_var), __KCSAN_ACCESS_RW(KCSAN_ACCESS_WRITE) },
+                       { test_kernel_atomic_builtin_with_memorder, &test_var, sizeof(test_var), __KCSAN_ACCESS_RW(0) },
+               },
+       };
+       bool match_expect = false;
+
+       test_struct.val[0] = 0; /* init unlocked */
+       begin_test_checks(test_kernel_atomic_builtin_with_memorder,
+                         test_kernel_atomic_builtin_with_memorder);
+       do {
+               match_expect = report_matches_any_reordered(&expect);
+       } while (!end_test_checks(match_expect));
+       KUNIT_EXPECT_FALSE(test, match_expect);
+}
+
+__no_kcsan
+static void test_atomic_builtins_missing_barrier(struct kunit *test)
+{
+       struct expect_report expect = {
+               .access = {
+                       { test_kernel_atomic_builtin_wrong_memorder, &test_var, sizeof(test_var), __KCSAN_ACCESS_RW(KCSAN_ACCESS_WRITE) },
+                       { test_kernel_atomic_builtin_wrong_memorder, &test_var, sizeof(test_var), __KCSAN_ACCESS_RW(0) },
+               },
+       };
+       bool match_expect = false;
+
+       test_struct.val[0] = 0; /* init unlocked */
+       begin_test_checks(test_kernel_atomic_builtin_wrong_memorder,
+                         test_kernel_atomic_builtin_wrong_memorder);
+       do {
+               match_expect = report_matches_any_reordered(&expect);
+       } while (!end_test_checks(match_expect));
+       if (IS_ENABLED(CONFIG_KCSAN_WEAK_MEMORY))
+               KUNIT_EXPECT_TRUE(test, match_expect);
+       else
+               KUNIT_EXPECT_FALSE(test, match_expect);
+}
+
 /*
  * Generate thread counts for all test cases. Values generated are in interval
  * [2, 5] followed by exponentially increasing thread counts from 8 to 32.
@@ -1088,6 +1396,7 @@ static const void *nthreads_gen_params(const void *prev, char *desc)
 
 #define KCSAN_KUNIT_CASE(test_name) KUNIT_CASE_PARAM(test_name, nthreads_gen_params)
 static struct kunit_case kcsan_test_cases[] = {
+       KUNIT_CASE(test_barrier_nothreads),
        KCSAN_KUNIT_CASE(test_basic),
        KCSAN_KUNIT_CASE(test_concurrent_races),
        KCSAN_KUNIT_CASE(test_novalue_change),
@@ -1112,6 +1421,10 @@ static struct kunit_case kcsan_test_cases[] = {
        KCSAN_KUNIT_CASE(test_seqlock_noreport),
        KCSAN_KUNIT_CASE(test_atomic_builtins),
        KCSAN_KUNIT_CASE(test_1bit_value_change),
+       KCSAN_KUNIT_CASE(test_correct_barrier),
+       KCSAN_KUNIT_CASE(test_missing_barrier),
+       KCSAN_KUNIT_CASE(test_atomic_builtins_correct_barrier),
+       KCSAN_KUNIT_CASE(test_atomic_builtins_missing_barrier),
        {},
 };
 
@@ -1176,6 +1489,9 @@ static int test_init(struct kunit *test)
        observed.nlines = 0;
        spin_unlock_irqrestore(&observed.lock, flags);
 
+       if (strstr(test->name, "nothreads"))
+               return 0;
+
        if (!torture_init_begin((char *)test->name, 1))
                return -EBUSY;
 
@@ -1218,6 +1534,9 @@ static void test_exit(struct kunit *test)
        struct task_struct **stop_thread;
        int i;
 
+       if (strstr(test->name, "nothreads"))
+               return;
+
        if (torture_cleanup_begin())
                return;