[patch 0/1] fix async usb removal

[Okash Khawaja]

On Wed, Aug 09, 2017 at 08:00:06PM +0200, Samuel Thibault wrote:
> Okash Khawaja, on mar. 08 ao??t 2017 06:51:58 +0100, wrote:
> > On Mon, Aug 07, 2017 at 11:18:44PM +0200, Samuel Thibault wrote:
> > > >  static void spk_ttyio_send_xchar(char ch)
> > > >  {
> > > > +	if (check_tty(speakup_tty))
> > > > +		return;
> > > > +
> > > >  	speakup_tty->ops->send_xchar(speakup_tty, ch);
> > > >  }
> > > 
> > > This is still unsafe: the unplug might come just between testing for
> > > speakup_tty becoming NULL and using it.
> > 
> > I thought about that but couldn't find a way to overcome it in a
> > foolproof way. Here's my reasoning. Since the unplugging of usb is
> > asynchronous to us calling methods on speakup_tty, speakup_tty can
> > become null in a separate thread.
> 
> Then more synchronization is needed: spk_ttyio_ldisc_close needs to
> wait for methods to be finished calling.  It would probably be enough
> to introduce a mere mutex that would be taken around the uses of
> speakup_tty, and in spk_ttyio_ldisc_close, so that it both waits for
> uses of speakup_tty, and delay others from happening.

I see what you mean. Thanks for clarifying.

Okash