selftests/vm: fix errno handling in mrelease_test

mrelease_test should return KSFT_SKIP when process_mrelease is not
defined, but due to a perror call consuming the errno, it returns
KSFT_FAIL.

This patch decides the exit code before calling perror.

[[e-mail]: fix remaining instances of errno mishandling]
Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 33776141b812 ("selftests: vm: add process_mrelease tests")
Signed-off-by: Adam Sindelar <[e-mail]>
Reviewed-by: David Vernet <[e-mail]>
Reviewed-by: Suren Baghdasaryan <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/testing/selftests/vm/mrelease_test.c

···
 /* The process_mrelease calls in this test are expected to fail */
 static void run_negative_tests(int pidfd)
 {
+	int res;
 	/* Test invalid flags. Expect to fail with EINVAL error code. */
 	if (!syscall(__NR_process_mrelease, pidfd, (unsigned int)-1) ||
 			errno != EINVAL) {
+		res = (errno == ENOSYS ? KSFT_SKIP : KSFT_FAIL);
 		perror("process_mrelease with wrong flags");
-		exit(errno == ENOSYS ? KSFT_SKIP : KSFT_FAIL);
+		exit(res);
 	}
 	/*
 	 * Test reaping while process is alive with no pending SIGKILL.
 	 * Expect to fail with EINVAL error code.
 	 */
 	if (!syscall(__NR_process_mrelease, pidfd, 0) || errno != EINVAL) {
+		res = (errno == ENOSYS ? KSFT_SKIP : KSFT_FAIL);
 		perror("process_mrelease on a live process");
-		exit(errno == ENOSYS ? KSFT_SKIP : KSFT_FAIL);
+		exit(res);
 	}
 }
 
···
 
 	/* Test a wrong pidfd */
 	if (!syscall(__NR_process_mrelease, -1, 0) || errno != EBADF) {
+		res = (errno == ENOSYS ? KSFT_SKIP : KSFT_FAIL);
 		perror("process_mrelease with wrong pidfd");
-		exit(errno == ENOSYS ? KSFT_SKIP : KSFT_FAIL);
+		exit(res);
 	}
 
 	/* Start the test with 1MB child memory allocation */
···
 	run_negative_tests(pidfd);
 
 	if (kill(pid, SIGKILL)) {
+		res = (errno == ENOSYS ? KSFT_SKIP : KSFT_FAIL);
 		perror("kill");
-		exit(errno == ENOSYS ? KSFT_SKIP : KSFT_FAIL);
+		exit(res);
 	}
 
 	success = (syscall(__NR_process_mrelease, pidfd, 0) == 0);
···
 		if (errno == ESRCH) {
 			retry = (size <= MAX_SIZE_MB);
 		} else {
+			res = (errno == ENOSYS ? KSFT_SKIP : KSFT_FAIL);
 			perror("process_mrelease");
 			waitpid(pid, NULL, 0);
-			exit(errno == ENOSYS ? KSFT_SKIP : KSFT_FAIL);
+			exit(res);
 		}
 	}