Allow CK to terminate on FreeBSD

[Joe Marcus Clarke]

On Tue, 2007-09-04 at 14:24 -0700, Remco Treffkorn wrote:
> On Friday 31 August 2007, Joe Marcus Clarke wrote:
> > On Fri, 2007-08-31 at 12:49 -0700, Remco Treffkorn wrote:
> > > On Friday 31 August 2007, Joe Marcus Clarke wrote:
> > > > I dug into the FreeBSD kernel some more, and found that if signal
> > > > handlers are registered, the tsleep() function will know which signals
> > > > are allowed to interrupt the ioctl syscall, thus causing it to return
> > > > EINTR.  Based on this, I put together this patch which fixes the
> > > > termination problem.  It may not be the ideal place for the signal
> > > > handler registration, but it does the job.
> > > >
> > > > I can send a formal git patch once people have a chance to comment.
> > > >
> > > > Joe
> > >
> > > So, the VT_WAITACTIVE ioctl returns EINTR when SIGTERM is sent to the
> > > process? The signal handler should now have been called already.
> >
> > It does now.  Before a signal handler is registered, there are no
> > signals in the sigintr set that can interrupt a syscall.
> >
> > > For me that sounds like fixing a symptom, since we really don't
> > > understand what the problem is.
> >
> > I know what the problem is now.  When VT_WAITACTIVE is called in
> > FreeBSD, the kernel puts the thread to sleep using the tsleep()
> > function.  This function will only return if the condition is met, or it
> > is interrupted.  If it is interrupted, but the signal is not in the
> > sigintr set, tsleep() will return ERESTART, and the ioctl will continue
> > to call tsleep() (it won't return to the caller since the caller didn't
> > indicate it wanted the syscall to be interrupted).
> >
> > Once a signal handler is registered for a signal, the sigintr set
> > becomes populated.  Now, tsleep() will check if the signal received is
> > in the set.  If it is, it returns EINTR, and the ioctl returns EINTR to
> > its caller (i.e. CK).  The result is the waiting thread continues.
> >
> > > Also, returning with EINTR only means the process received a signal. Does
> > > not have to be SIGTERM.
> >
> > Correct.  However, since we had to explicitly register handlers for
> > those signals we wanted to cause aborts, we can safely assume that if
> > ioctl returns EINTR in this case (at least on FreeBSD) our process has
> > received one of SIGTERM, SIGQUIT, SIGHUP, or SIGINT, and we should die.
> >
> > Joe
> 
> I had some time to think about it, and it still disturbs me.

I have been working with the kernel guys on this, and the underlying
kernel loop will be fixed.  However, it will take time to propagate to
all versions of FreeBSD.

> The diff only had the BSD conditional in it. Where is the signal handler for 
> SIGTERM, SIGQUIT, SIGHUP, and SIGINT? Why not just exit from there?

In the meantime, simply registering SIG_DFL for SIGTERM, SIGQUIT,
SIGHUP, and SIGINT will work to terminate the process in the normal
cases.

> 
> You will then never even get to the goto.

I have a new patch that simply removes the #ifdef around that goto.
It's not needed.

> 
> How is SIGKILL handled? You indicated BDS had a bug. Are you still saying 
> that?

SIGKILL is not handled because of the loop in the kernel.  Yes it is a
bug, and it will be fixed, but CK will still need a BSD workaround in
the meantime.

Joe

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