tests: mem_protect: fix corruption issue

This test has a problem, specifically in the scenario for
test_mem_domain_remove_partitions. A low priority thread (10)
is created which is expected to produce an exception. Then
the following happens:

- The thread indeed crashes and ends up in the custom fatal
  error handler, on the stack used for exceptions
- The call to ztest_test_pass() is made
- ztest_test_pass() gives the test_end_signal semaphore
- We then context switch to the ztest main thread which is
  higher priority, leaving the thread that crashed context
  switched out *on the exception stack*
- More tests are run, and some of them also produce exceptions
- Eventually we do a sleep and the original crashed thread is
  swapped in again
- Since several other exceptions have taken place on the
  exception stack since then, resuming context results in
  an unexpected error, causing the test to fail

Only seems to affect arches that have a dedicated stack for
exceptions, like x86_64. For now, increase the priority of
the child thread so it's cleaned up immediately. Longer-term,
this all needs to be re-thought in the test case to make this
less fragile.

Signed-off-by: Andrew Boie <[email protected]>

Author: Andrew Boie

tests/kernel/mem_protect/mem_protect/src/mem_domain.c

@@ -91,7 +91,7 @@ static inline void set_valid_fault_value(int test_case_number)
 /* Userspace function */
 void mem_domain_for_user(void *tc_number, void *p2, void *p3)
 {
-	set_valid_fault_value((uintptr_t)tc_number);
+	set_valid_fault_value((int)tc_number);
 
 	mem_domain_buf[0] = 10U;
 	if (valid_fault == false) {
@@ -523,7 +523,7 @@ void test_mem_domain_remove_partitions(void *p1, void *p2, void *p3)
 			MEM_DOMAIN_STACK_SIZE,
 			mem_domain_test_6_1,
 			NULL, NULL, NULL,
-			10, K_USER | K_INHERIT_PERMS, K_NO_WAIT);
+			-1, K_USER | K_INHERIT_PERMS, K_NO_WAIT);
 
 
 	k_sem_take(&sync_sem, K_MSEC(100));
@@ -536,7 +536,7 @@ void test_mem_domain_remove_partitions(void *p1, void *p2, void *p3)
 			MEM_DOMAIN_STACK_SIZE,
 			mem_domain_test_6_2,
 			NULL, NULL, NULL,
-			10, K_USER | K_INHERIT_PERMS, K_NO_WAIT);
+			-1, K_USER | K_INHERIT_PERMS, K_NO_WAIT);
 
 	k_sem_take(&sync_sem, SYNC_SEM_TIMEOUT);