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bh=cTeoROhLTJNSMiknI8ur7+S5MZYfjz8iBQVTs5miYU0=; b=BmFygw9K+ImTq0Iqj3IhmJ6pfFbTz8M2VRQtKSxBiIRq9qliT1qma/YRoNLhbdAC31sd06Zf2asH6g7v/GecFSPq7xxyd6AenvwjWgh5Du/knj6sbIKTlXrfNNGtG6pr3/nAFLqaWRASzdx1q3S0iY04J5pVEPizkL8RLKzktAjIlPBKON9qXK6FiXZ3l/bZp+sZyavchDtPvHdYr5CQJ8CoJP4XtSuhrX+rJaxkgsOHQWCV/qGabgELQyBjXbo/izfhW/sIhOPyt9XudNvo4rrb980YkO1K993z1jZzQdIDNKG2/gL6Vtim98Lv01Pmme1IyMbZra8A4lv0B3CaTA== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=cornell.edu; dmarc=pass action=none header.from=cornell.edu; dkim=pass header.d=cornell.edu; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cornell.edu; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=cTeoROhLTJNSMiknI8ur7+S5MZYfjz8iBQVTs5miYU0=; b=F1S0UbL2F7unJzwo6G5Mwuft2IHHx4fyz9PP46+dVTf6t8T/29Ms3+smMi0O/ywp+I5JhXscL3WVRjYtbUC2vBB7pcQtJHX+Y0kdLYPWU65BdygRoyu03iL5aU2k/LUTsqHcvpIn3Wi/M1wlmsofN0F1VkUfG3j5h29rgqnpLP8= From: Ken Brown To: "cygwin AT cygwin DOT com" Subject: Re: ssh-agent doesn't die Date: Fri, 4 Oct 2019 20:13:36 +0000 Message-ID: <81400f03-e424-255a-7b94-d3cbe584c356@cornell.edu> References: <319e26c0-32f0-40b7-2137-c7de170a3486 AT rl DOT ac DOT uk> <5b225738-c2d7-fbfe-48a7-8c2a38c3398c AT cornell DOT edu> <0ccd17b6-c22a-1a18-9409-1ebcfae60868 AT huarp DOT harvard DOT edu> <9f7a14bb-f81b-c566-bb84-8da7fc6d0fad AT cornell DOT edu> <185c5774-dd8b-5488-b818-4cec5a24bf2d AT cornell DOT edu> <801bca17-2c61-bb6a-f02c-c4912232d9c5 AT cornell DOT edu> In-Reply-To: <801bca17-2c61-bb6a-f02c-c4912232d9c5@cornell.edu> user-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 authentication-results: spf=none (sender IP is ) smtp.mailfrom=kbrown AT cornell DOT edu; x-ms-oob-tlc-oobclassifiers: OLM:9508; received-spf: None (protection.outlook.com: cornell.edu does not designate permitted sender hosts) x-ms-exchange-senderadcheck: 1 x-ms-exchange-transport-forked: True Content-Type: text/plain; charset="Windows-1252" Content-ID: <67457FA75E85FA409971C675E05CD14B AT namprd04 DOT prod DOT outlook DOT com> MIME-Version: 1.0 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: nrHR6n1cQoQEh5nuU9/kF/ctunU7LK67O02ELq/rG5A4JXg6pQD9SKqk2t2MozpUifFegRYHStjgZnbno8QtkQ== X-IsSubscribed: yes Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by delorie.com id x94KEDdT020131 On 10/4/2019 10:27 AM, Ken Brown wrote: > On 9/29/2019 4:05 PM, Ken Brown wrote: >> On 9/27/2019 10:12 AM, Ken Brown wrote: >>> On 9/27/2019 9:37 AM, Norton Allen wrote: >>>> On 9/26/2019 10:50 PM, Ken Brown wrote: >>>>> >>>>>> As a simple test example, consider: >>>>>> >>>>>> /bin/ssh-agent /bin/sleep 10 >>>>>> >>>>>> While the sleep is still running, ps shows: >>>>>> >>>>>> PID PPID PGID WINPID TTY UID STIME COMMAND >>>>>> 1694 1693 1694 1576 ? 22534 00:01:10 >>>>>> /usr/bin/ssh-agent >>>>>> 1653 1 1653 11740 cons1 22534 00:00:37 /usr/bin/bash >>>>>> 1693 1653 1693 1552 cons1 22534 00:01:10 /usr/bin/sleep >>>>>> >>>>>> One oddity is that ssh-agent is listed as a subprocess of sleep >>>>> ...but this isn't a bug. ssh-agent forks, and then the parent execs the command. >>>> >>>> With the salient difference presumably being that the exec is done in the parent >>>> instead of the child as usual? >>> >>> Yes. The idea is that 'ssh-agent command' should be more-or-less equivalent to >>> running 'command', with ssh-agent running as a subprocess. >>> >>> The ssh-agent subprocess periodically checks to see if its parent is still >>> alive, and it exits when the parent has died. Someone should figure out why >>> this is not working on Cygwin. >> >> As an aid to someone who might want to debug this (probably Corinna when she >> returns), I've created a test program agent.c (attached) that simulates the >> relevant part of ssh-agent: >> >> 1. It forks a subprocess that periodically checks to see if its parent has died, >> and then exits. >> >> 2. The parent execs "/usr/bin/sleep 1". >> >> As with ssh-agent, the subprocess never detects that the parent has died, and so >> it never exits. >> >> Running this program under strace shows the following error in the pinfo >> constructor: >> >> pinfo::pinfo: couldn't duplicate parent rd_proc_pipe handle 0x1BC for forked >> child 1666 after exec, Win32 error 5 >> >> [Win32 error 5 is ERROR_ACCESS_DENIED.] > > It seems that the pinfo constructor failure happens in > cygheap_exec_info::reattach_children(). The latter is preceded by the following > comment: > > /* Reattach non-reaped subprocesses passed in from the cygwin process > which previously operated under this pid. FIXME: Is there a race here > if the process exits during cygwin's exec handoff? */ > > I tried running my test program under gdb with a breakpoint at > reattach_children, and the breakpoint was never hit. That gives an affirmative > answer to the question in the FIXME. > > As a result, the exec'd program never becomes aware that it has a subprocess, so > it exits without resetting the subprocess's ppid to 1. > > Is there someone out there familiar enough with Cygwin's exec to suggest a fix? > It would be a nice gift to Corinna to get this fixed before her return. What I said above about gdb is nonsense. It's the exec'd process that calls reattach_children, so I wouldn't expect gdb to see that call. I think the rest of my analysis is correct, but I'm not sure that the FIXME explains the failure. Ken -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple