Merge tag 'kselftest-fix-2024-07-04' of git://git.kernel.org/pub/scm/linux/kernel/git/mic/linux

Pull Kselftest fix from Mickaël Salaün:
 "Fix Kselftests timeout.

  We can't use CLONE_VFORK, since that blocks the parent - and thus the
  timeout handling - until the child exits or execve's.

  Go back to using plain fork()"

* tag 'kselftest-fix-2024-07-04' of git://git.kernel.org/pub/scm/linux/kernel/git/mic/linux:
  selftests/harness: Fix tests timeout and race condition

Author: torvalds

tools/testing/selftests/kselftest_harness.h

@@ -66,8 +66,6 @@
 #include <sys/wait.h>
 #include <unistd.h>
 #include <setjmp.h>
-#include <syscall.h>
-#include <linux/sched.h>
 
 #include "kselftest.h"
 
@@ -82,17 +80,6 @@
 #  define TH_LOG_ENABLED 1
 #endif
 
-/* Wait for the child process to end but without sharing memory mapping. */
-static inline pid_t clone3_vfork(void)
-{
-	struct clone_args args = {
-		.flags = CLONE_VFORK,
-		.exit_signal = SIGCHLD,
-	};
-
-	return syscall(__NR_clone3, &args, sizeof(args));
-}
-
 /**
  * TH_LOG()
  *
@@ -437,7 +424,7 @@ static inline pid_t clone3_vfork(void)
 		} \
 		if (setjmp(_metadata->env) == 0) { \
 			/* _metadata and potentially self are shared with all forks. */ \
-			child = clone3_vfork(); \
+			child = fork(); \
 			if (child == 0) { \
 				fixture_name##_setup(_metadata, self, variant->data); \
 				/* Let setup failure terminate early. */ \
@@ -1016,7 +1003,14 @@ void __wait_for_test(struct __test_metadata *t)
 		.sa_flags = SA_SIGINFO,
 	};
 	struct sigaction saved_action;
-	int status;
+	/*
+	 * Sets status so that WIFEXITED(status) returns true and
+	 * WEXITSTATUS(status) returns KSFT_FAIL.  This safe default value
+	 * should never be evaluated because of the waitpid(2) check and
+	 * SIGALRM handling.
+	 */
+	int status = KSFT_FAIL << 8;
+	int child;
 
 	if (sigaction(SIGALRM, &action, &saved_action)) {
 		t->exit_code = KSFT_FAIL;
@@ -1028,7 +1022,15 @@ void __wait_for_test(struct __test_metadata *t)
 	__active_test = t;
 	t->timed_out = false;
 	alarm(t->timeout);
-	waitpid(t->pid, &status, 0);
+	child = waitpid(t->pid, &status, 0);
+	if (child == -1 && errno != EINTR) {
+		t->exit_code = KSFT_FAIL;
+		fprintf(TH_LOG_STREAM,
+			"# %s: Failed to wait for PID %d (errno: %d)\n",
+			t->name, t->pid, errno);
+		return;
+	}
+
 	alarm(0);
 	if (sigaction(SIGALRM, &saved_action, NULL)) {
 		t->exit_code = KSFT_FAIL;
@@ -1083,6 +1085,7 @@ void __wait_for_test(struct __test_metadata *t)
 				WTERMSIG(status));
 		}
 	} else {
+		t->exit_code = KSFT_FAIL;
 		fprintf(TH_LOG_STREAM,
 			"# %s: Test ended in some other way [%u]\n",
 			t->name,
@@ -1218,6 +1221,7 @@ void __run_test(struct __fixture_metadata *f,
 	struct __test_xfail *xfail;
 	char test_name[1024];
 	const char *diagnostic;
+	int child;
 
 	/* reset test struct */
 	t->exit_code = KSFT_PASS;
@@ -1236,15 +1240,16 @@ void __run_test(struct __fixture_metadata *f,
 	fflush(stdout);
 	fflush(stderr);
 
-	t->pid = clone3_vfork();
-	if (t->pid < 0) {
+	child = fork();
+	if (child < 0) {
 		ksft_print_msg("ERROR SPAWNING TEST CHILD\n");
 		t->exit_code = KSFT_FAIL;
-	} else if (t->pid == 0) {
+	} else if (child == 0) {
 		setpgrp();
 		t->fn(t, variant);
 		_exit(t->exit_code);
 	} else {
+		t->pid = child;
 		__wait_for_test(t);
 	}
 	ksft_print_msg("         %4s  %s\n",