Re: acm_port_shutdown hangs for 30 seconds

[Jookia <contact@jookia.org>]

On Wed, Jun 29, 2022 at 02:01:18PM +0200, Oliver Neukum wrote:
> You have something in the buffer, which the tty layer will try to send.
> 
> > In userspace the hang happens at a call to close() on the TTY, and using
> 
> The tty layer is supposed to wait a defined amount of time
> if a tty needs to drain.
> This amount (among many other things) is traditionally
> set with the TIOCSSERIAL ioctl()
> 
> > perf and ftrace it looks to be spending a lot of time poisoning urbs in
> > acm_port_shutdown.
> 
> That is a bit odd.
> 
> > - Is this a bug?
> 
> Maybe, but unlikely. If and only it takes much more time than the
> termios say.
> 
> > - Can I reduce the timeout somehow?
> 
> ioctl() TIOCSSERIAL. If that does not work,
> it's a bug.

This sounds like exactly what's happening. Next time I hit this issue
I'll see if changing closing_wait fixes this.

> 	HTH
> 		Oliver