Re: [PATCH] PR threads/20743: Don't attempt to suspend or resume exited threads.

[John Baldwin <jhb at freebsd dot org>]

On Wednesday, December 28, 2016 09:07:07 AM Vasil Dimov wrote:
> On Tue, Dec 27, 2016 at 13:03:27 -0800, John Baldwin wrote:
> [...]
> > I have tried changing fbsd_wait() to return a TARGET_WAITKIND_SPURIOUS
> > instead of explicitly continuing the process, but that doesn't help, and it
> > means that the ptid being returned is still T1 in that case.
> > 
> > I'm not sure if I should explicitly be calling delete_exited_threads() in
> > fbsd_resume() before calling iterate_threads()?  Alternatively, fbsd_resume()
> > could use ALL_NONEXITED_THREADS() instead of iterate_threads() (it isn't
> > clear to me which of these is preferred since both are in use).
> > 
> > I added the assertion for my own sanity.  I suspect gdb should never try to
> > invoke target_resume() with a ptid of an exited thread, but if for some
> > reason it did the effect on FreeBSD would be a hang since we would suspend
> > all the other threads and when the process was continued via PT_CONTINUE it
> > would have nothing to do and would never return from wait().  I'd rather have
> > gdb fail an assertion in that case rather than hang.
> [...]
> 
> Hi,
> 
> I am not sure if this is related, but since I get a hang I would rather
> mention it: with the John's patch (including the assert) gdb does not
> emit the "ptrace: No such process" error, but when I attempt to quit,
> it hangs:

No, this is a separate bug in the kernel whereby a process doesn't
treat PT_KILL as a detach-like event but incorrectly expects to keep
getting PT_CONTINUE events for a while until it finally exits.  I'm
working on writing up regression/unit tests for PT_KILL and then
fixing the bug.

-- 
John Baldwin