Re: [PATCH 1/1] um: fix error return code in winch_tramp()

[Johannes Berg <johannes@sipsolutions.net>]

On Fri, 2022-05-20 at 08:55 -0700, Nathan Chancellor wrote:
> On Fri, May 20, 2022 at 08:08:01AM +0200, Thorsten Leemhuis wrote:
> > On 11.04.22 20:45, Richard Weinberger wrote:
> > > ----- Ursprüngliche Mail -----
> > > > Von: "Nathan Chancellor" <nathan@kernel.org>
> > > > I attempted to print out the error code but it seems like there is no
> > > > output in the console after "reboot: System halted". If I add an
> > > > unconditional print right before the call to os_set_fd_block(), I see it
> > > > during start up but I do not see it during shutdown. Is there some way
> > > > to see that console output during shutdown?
> > > 
> > > I think in this case the easiest way is attaching gdb with a breakpoint.
> > 
> > I noticed this in my list of open regressions. It seems there wasn't any
> > progress to get this regression fixed (please let me know in case I
> > missed something), but I guess nobody considered it urgent which is
> > likely not that much of a problem in this case.
> 
> Yes, sorry, I tried to get gdb to reveal something but I couldn't get it
> to work then I had to move onto other work. We have worked around this
> for the time being but it would still be nice to figure out what is
> going on here; I am just not sure when I am going to have time to
> participate in that process.
> 

This fixes it for me, can you check it?

diff --git a/arch/um/drivers/chan_user.c b/arch/um/drivers/chan_user.c
index 6040817c036f..25727ed648b7 100644
--- a/arch/um/drivers/chan_user.c
+++ b/arch/um/drivers/chan_user.c
@@ -220,7 +220,7 @@ static int winch_tramp(int fd, struct tty_port *port, int *fd_out,
 		       unsigned long *stack_out)
 {
 	struct winch_data data;
-	int fds[2], n, err;
+	int fds[2], n, err, pid;
 	char c;
 
 	err = os_pipe(fds, 1, 1);
@@ -238,8 +238,9 @@ static int winch_tramp(int fd, struct tty_port *port, int *fd_out,
 	 * problem with /dev/net/tun, which if held open by this
 	 * thread, prevents the TUN/TAP device from being reused.
 	 */
-	err = run_helper_thread(winch_thread, &data, CLONE_FILES, stack_out);
-	if (err < 0) {
+	pid = run_helper_thread(winch_thread, &data, CLONE_FILES, stack_out);
+	if (pid < 0) {
+		err = pid;
 		printk(UM_KERN_ERR "fork of winch_thread failed - errno = %d\n",
 		       -err);
 		goto out_close;
@@ -263,7 +264,7 @@ static int winch_tramp(int fd, struct tty_port *port, int *fd_out,
 		goto out_close;
 	}
 
-	return err;
+	return pid;
 
  out_close:
 	close(fds[1]);


Kind of obvious, really. :)

johannes