Date: Sun, 24 Nov 2019 13:39:56 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Kyle Evans <kevans@freebsd.org> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: ptrace(2) debugging Message-ID: <20191124113956.GY2707@kib.kiev.ua> In-Reply-To: <CACNAnaHtsAaULLp0icE_=vY4eq2CuJ6Oq4Zx868axaYXArSOeQ@mail.gmail.com> References: <CACNAnaHtsAaULLp0icE_=vY4eq2CuJ6Oq4Zx868axaYXArSOeQ@mail.gmail.com>
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On Sun, Nov 24, 2019 at 12:01:04AM -0600, Kyle Evans wrote: > Hi, > > I'm working on implementing `reptyr -T` on FreeBSD because I'm pretty > bad about starting long-running jobs outside of tmux and often desire > to reparent these jobs into tmux. I've gotten to a point where it's > getting stuck in waitpid(2) when attempting to work over the session > leader to ignore SIGHUP. The chain of operations looks roughly like > this: > > PT_ATTACH -> waitpid -> kill(SIGCONT) -> PT_TO_SCE -> waitpid -> > PT_TO_SCE -> waitpid > > Each of the waitpids are paired with a PT_LWPINFO. The first waitpid > observes SIGSTOP. The second waitpid observes SIGCONT. I would expect > the third to observe PL_FLAG_SCE on ptrace_lwpinfo->pl_flags, but > instead it actually hangs as the target process is now sleep-inhibited > and stuck in "pause" wchan. > > I've uploaded a truss excerpt at [0] in case it's helpful -- pid=10204 > is the process I'm reparenting, initially just attached/detached to > make sure reptyr *can* do this. pid=10187 is the sshd that it's > running under, and pid=10188 is the shell running under that. > > Anyone have good advice on debugging this? It seems like it might be > some kind of kernel bug, as it's already done this same dance once > before when grabbing sshd and my attempts to distill it down to a > simple test case failed. The FreeBSD part of reptyr needed some love, > though, so that can't be discounted either. > > Thanks, > > Kyle Evans > > [0] https://people.freebsd.org/~kevans/truss.log How much work would be to provide a self-contained standalone test ?
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