um: Switch to the pthread-based helper in sigio workaround

The write_sigio thread and UML kernel thread share the same errno,
which can lead to conflicts when both call syscalls concurrently.
Switch to the pthread-based helper to address this issue.

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20250319135523.97050-4-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: btw616

arch/um/os-Linux/sigio.c

@@ -21,8 +21,7 @@
  * Protected by sigio_lock(), also used by sigio_cleanup, which is an
  * exitcall.
  */
-static int write_sigio_pid = -1;
-static unsigned long write_sigio_stack;
+static struct os_helper_thread *write_sigio_td;
 
 /*
  * These arrays are initialized before the sigio thread is started, and
@@ -48,15 +47,15 @@ static struct pollfds current_poll;
 static struct pollfds next_poll;
 static struct pollfds all_sigio_fds;
 
-static int write_sigio_thread(void *unused)
+static void *write_sigio_thread(void *unused)
 {
 	struct pollfds *fds, tmp;
 	struct pollfd *p;
 	int i, n, respond_fd;
 	char c;
 
-	os_set_pdeathsig();
-	os_fix_helper_signals();
+	os_fix_helper_thread_signals();
+
 	fds = &current_poll;
 	while (1) {
 		n = poll(fds->poll, fds->used, -1);
@@ -98,7 +97,7 @@ static int write_sigio_thread(void *unused)
 		}
 	}
 
-	return 0;
+	return NULL;
 }
 
 static int need_poll(struct pollfds *polls, int n)
@@ -152,11 +151,10 @@ static void update_thread(void)
 	return;
  fail:
 	/* Critical section start */
-	if (write_sigio_pid != -1) {
-		os_kill_process(write_sigio_pid, 1);
-		free_stack(write_sigio_stack, 0);
+	if (write_sigio_td) {
+		os_kill_helper_thread(write_sigio_td);
+		write_sigio_td = NULL;
 	}
-	write_sigio_pid = -1;
 	close(sigio_private[0]);
 	close(sigio_private[1]);
 	close(write_sigio_fds[0]);
@@ -220,7 +218,7 @@ int __ignore_sigio_fd(int fd)
 	 * sigio_cleanup has already run, then update_thread will hang
 	 * or fail because the thread is no longer running.
 	 */
-	if (write_sigio_pid == -1)
+	if (!write_sigio_td)
 		return -EIO;
 
 	for (i = 0; i < current_poll.used; i++) {
@@ -279,14 +277,14 @@ static void write_sigio_workaround(void)
 	int err;
 	int l_write_sigio_fds[2];
 	int l_sigio_private[2];
-	int l_write_sigio_pid;
+	struct os_helper_thread *l_write_sigio_td;
 
 	/* We call this *tons* of times - and most ones we must just fail. */
 	sigio_lock();
-	l_write_sigio_pid = write_sigio_pid;
+	l_write_sigio_td = write_sigio_td;
 	sigio_unlock();
 
-	if (l_write_sigio_pid != -1)
+	if (l_write_sigio_td)
 		return;
 
 	err = os_pipe(l_write_sigio_fds, 1, 1);
@@ -312,7 +310,7 @@ static void write_sigio_workaround(void)
 	 * Did we race? Don't try to optimize this, please, it's not so likely
 	 * to happen, and no more than once at the boot.
 	 */
-	if (write_sigio_pid != -1)
+	if (write_sigio_td)
 		goto out_free;
 
 	current_poll = ((struct pollfds) { .poll 	= p,
@@ -325,18 +323,15 @@ static void write_sigio_workaround(void)
 	memcpy(write_sigio_fds, l_write_sigio_fds, sizeof(l_write_sigio_fds));
 	memcpy(sigio_private, l_sigio_private, sizeof(l_sigio_private));
 
-	write_sigio_pid = run_helper_thread(write_sigio_thread, NULL,
-					    CLONE_FILES | CLONE_VM,
-					    &write_sigio_stack);
-
-	if (write_sigio_pid < 0)
+	err = os_run_helper_thread(&write_sigio_td, write_sigio_thread, NULL);
+	if (err < 0)
 		goto out_clear;
 
 	sigio_unlock();
 	return;
 
 out_clear:
-	write_sigio_pid = -1;
+	write_sigio_td = NULL;
 	write_sigio_fds[0] = -1;
 	write_sigio_fds[1] = -1;
 	sigio_private[0] = -1;
@@ -394,12 +389,11 @@ void maybe_sigio_broken(int fd)
 
 static void sigio_cleanup(void)
 {
-	if (write_sigio_pid == -1)
+	if (!write_sigio_td)
 		return;
 
-	os_kill_process(write_sigio_pid, 1);
-	free_stack(write_sigio_stack, 0);
-	write_sigio_pid = -1;
+	os_kill_helper_thread(write_sigio_td);
+	write_sigio_td = NULL;
 }
 
 __uml_exitcall(sigio_cleanup);