linux-kernel - Re: [PATCH 07/10] TTY: switch tty_schedule

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Date:	Fri, 01 Feb 2013 15:39:31 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	Jiri Slaby <jirislaby@...il.com>, gregkh@...uxfoundation.org,
	alan@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/10] TTY: switch tty_schedule_flip

On Fri, 2013-02-01 at 16:06 +0100, Jiri Slaby wrote:
> On 02/01/2013 01:37 PM, Peter Hurley wrote:
> > On Thu, 2013-01-03 at 15:53 +0100, Jiri Slaby wrote:
> >> Now, we start converting tty buffer functions to actually use
> >> tty_port. This will allow us to get rid of the need of tty in many
> >> call sites. Only tty_port will needed and hence no more
> >> tty_port_tty_get in those paths.
> >>
> >> This is the last one: tty_schedule_flip
> > 
> > [snip]
> > 
> >> diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
> >> index 5aace4d..a9af1b9a 100644
> >> --- a/drivers/tty/vt/keyboard.c
> >> +++ b/drivers/tty/vt/keyboard.c
> >> @@ -307,26 +307,17 @@ int kbd_rate(struct kbd_repeat *rep)
> >>   */
> >>  static void put_queue(struct vc_data *vc, int ch)
> >>  {
> >> -	struct tty_struct *tty = vc->port.tty;
> >> -
> >>  	tty_insert_flip_char(&vc->port, ch, 0);
> >> -	if (tty) {
> >> -		tty_schedule_flip(tty);
> >> -	}
> >> +	tty_schedule_flip(&vc->port);
> >>  }
> >>  
> >>  static void puts_queue(struct vc_data *vc, char *cp)
> >>  {
> >> -	struct tty_struct *tty = vc->port.tty;
> >> -
> >> -	if (!tty)
> >> -		return;
> >> -
> >>  	while (*cp) {
> >>  		tty_insert_flip_char(&vc->port, *cp, 0);
> >>  		cp++;
> >>  	}
> >> -	tty_schedule_flip(tty);
> >> +	tty_schedule_flip(&vc->port);
> >>  }
> > 
> > Umm. So even though the vt driver knows the tty has been shutdown,
> > keystrokes will still be buffered? And then fed to whichever tty happens
> > to next get installed on the same port?
> 
> Unless I completely missed something, they should be flushed. If that's
> not the case, that's a bug. I will check next week.

Ok.

I'm fairly sure this is happening. Try repeatedly tapping arrow-down
while booting (I suggest a VM) and you won't be able to login at tty1
(ie, text mode). Repeatable 1 time in 5 or so.

FWIW, I don't agree that the best way is to flush the flip buffers. Why
buffer and then schedule the cpu to do work which we already know it
can't do and which we're going to discard anyway?

In any event, since -next is already carrying these patches, and
by-design, these patches _expect_ the tty to be NULL, are you going to
remove the warning in flush_to_ldisc() or shall I?

Regards,
Peter Hurley



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