From owner-freebsd-hackers@freebsd.org Sun Nov 24 11:40:11 2019 Return-Path: Delivered-To: freebsd-hackers@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 3AC7A1AC0A6 for ; Sun, 24 Nov 2019 11:40:11 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 47LSrq00pDz3R1g; Sun, 24 Nov 2019 11:40:10 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id xAOBdudj013776 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Sun, 24 Nov 2019 13:39:59 +0200 (EET) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua xAOBdudj013776 Received: (from kostik@localhost) by tom.home (8.15.2/8.15.2/Submit) id xAOBdub9013775; Sun, 24 Nov 2019 13:39:56 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Sun, 24 Nov 2019 13:39:56 +0200 From: Konstantin Belousov To: Kyle Evans Cc: FreeBSD Hackers Subject: Re: ptrace(2) debugging Message-ID: <20191124113956.GY2707@kib.kiev.ua> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.2 (2019-09-21) X-Spam-Status: No, score=-1.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FORGED_GMAIL_RCVD,FREEMAIL_FROM, NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on tom.home X-Rspamd-Queue-Id: 47LSrq00pDz3R1g X-Spamd-Bar: ----- Authentication-Results: mx1.freebsd.org; none X-Spamd-Result: default: False [-5.99 / 15.00]; NEURAL_HAM_MEDIUM(-1.00)[-0.996,0]; NEURAL_HAM_LONG(-1.00)[-0.997,0]; REPLY(-4.00)[] X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 24 Nov 2019 11:40:11 -0000 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 ?