[ConsoleKit] Active VT tracking can fail at startup

Ray Strode halfline at gmail.com
Tue Aug 24 07:08:58 PDT 2010


On Mon, Aug 23, 2010 at 6:30 PM, Leen Besselink
<consolekit at consolejunkie.net> wrote:
> The last few days I've been trying to fix an issue with consolekit which
> I noticed when I did an upgrade (clean install) of Ubuntu on a laptop I
> had lying around.
> It doesn't seem to be Ubuntu specific though.
> The issue seems, to me atleast, that when consolekit starts up, it grabs
> the console_fd so it can do it can start the threads and do the ioctl
> for VT_WAITACTIVE for each vt.
> Then I think the kernel does a mode change (kernel mode setting) of the
> console and when consolekit wants to start the threads and use the
> console_fd it isn't valid anymore and fails.
Nah, I doubt modesetting is causing that kind of problem.  If it is,
that's probably a kernel bug that should get fixed. Are you sure it's
caused by modesetting and not just something happening around the same
time? Do it happen if you don't do modesetting at boot time and then
do it manually with modprobe later?

It's more likely something is stealing the tty away, causing a hangup I think.

The ck_get_a_console_fd () function looks pretty bogus.

If it's being used for VT_WAITACTIVE it should be passing the fd to a
tty associated with a vt, but looking at the function I see it tries
/dev/tty before trying /dev/tty0.

/dev/tty is the tty of the controlling terminal of the currently
running process.  consolekit is daemon, so it shouldn't have a
controlling terminal.  It could be that ck is getting started with
--no-daemon though. In that case it might be picking up the
controlling tty of whatever it was started from.  If another process
took the same controlling terminal, it could cause a hangup to be sent
to console kit on the fd.  I basically don't think ck should be using
/dev/tty at all.

After trying /dev/tty it tries /dev/tty0.  That's a good one to use.
It's the vt "master" tty.

Do you get better results if you just drop the /dev/tty / _PATH_TTY stuff?

If not, I think the first thing to do is figure out what actually is
causing the hangup, next would be to figure whether we should stop it
from causing the hangup or change consolekit to reopen its tty when it
gets a hangup.


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