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Re: hangup in close(2) after posix_openpt(3)
On Sun, Oct 18, 2015 at 11:33:43AM +0900, Izumi Tsutsui wrote:
> > > > On Sat, Oct 17, 2015 at 03:23:44PM +0900, Izumi Tsutsui wrote:
> > > > > I notice we can avoid the hangup in lwp_park() after exit(3)
> > > > > by calling _exit(2) instead exit(3) in the parent canuum,
> > > > > so I'll put it as a kludge for now.
> > > >
> > > > Be careful, that bypasses all atexit handler. The reason why it might
> > > > work is that this includes the fflush of stdin and stdout.
> > >
> > > Do you have any idea about "hangup in lwp_park() after exit(3)"?
> > > Is it a bug, or expected behavior?
> > >
> > > Currently the hangup in lwp_park() (which can be killed only by kill -9)
> > > is much annoying than _exit(2) kludge.
> > lwp_park is what happens when a threaded process is blocked, so my
> > first guess would be an application-level deadlock.
> Hmm, even after exit(3)?
All it takes is an atexit handler that takes a mutex, and an exit in
an unfortunate place...
> Could posix_openpt(3) + fork(2)/execvp(3) (or curses(3)) without pthread
> cause such deadlock?
I would be surprised if lwp_park appeared in such a deadlock.
Although, if you have a threaded process make sure you check all the
process's lwps; it might be that one is stuck on the tty while holding
a mutex needed by another one.
David A. Holland
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