From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 40300 invoked by alias); 11 Aug 2016 09:52:01 -0000 Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner@cygwin.com Mail-Followup-To: cygwin@cygwin.com Received: (qmail 40283 invoked by uid 89); 11 Aug 2016 09:52:00 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.6 required=5.0 tests=BAYES_00,FREEMAIL_FROM,RCVD_IN_DNSWL_LOW,SPF_PASS autolearn=ham version=3.3.2 spammy=covers, lifetime, acted, subscribed X-HELO: mail-wm0-f65.google.com Received: from mail-wm0-f65.google.com (HELO mail-wm0-f65.google.com) (74.125.82.65) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES128-GCM-SHA256 encrypted) ESMTPS; Thu, 11 Aug 2016 09:51:43 +0000 Received: by mail-wm0-f65.google.com with SMTP id i138so324174wmf.3 for ; Thu, 11 Aug 2016 02:51:43 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:from:date:message-id:subject:to; bh=TNWj4HJ6ztfAxnpirQt0A0PhsfcUGcPbDhHbAkddDWw=; b=NgH+KuI1nV7MULSqkhtZ+y2AikP03eOh9HnFlDLgcMT/ZarsAdn8Evsdc13sbiHg5N 3Oc6cciofReYP26ri0BAyKfY2HHJtC9XFfO6jF3TniRvxZwsPYwQAnC8PcUR2/BtRRsW DihchsBXfyhTxUqHqPb9arsHeE5n2HSLWlE9poAKWjwdt8YPf3LtV3oIzJV9ZLhPczJx 4zxetmDcgOQhROeW/JgCWnAsTFctHnS54r4wJYK1IsuoEgrM11IZ2eBZfHdE+H87PuCH mu0KAG5Bq7bmlEpUztbWhQLbTCoge5aCK5bP+sCth9tf8sclggJUwEXw7MMDGV9az/Ta Tz2Q== X-Gm-Message-State: AEkoous4ml51hRPl7Vdw6vMprKp1XWQEszpfUWpOV+tm3RWDgvzKvduoqLWwECFAD52EIfvQfhRla7LYsRA31A== X-Received: by 10.25.219.210 with SMTP id t79mr1366286lfi.110.1470909100450; Thu, 11 Aug 2016 02:51:40 -0700 (PDT) MIME-Version: 1.0 Received: by 10.25.76.69 with HTTP; Thu, 11 Aug 2016 02:51:39 -0700 (PDT) From: Erik Bray Date: Thu, 11 Aug 2016 13:39:00 -0000 Message-ID: Subject: 2.5.1: kill(pid, sig) before waitpid() returns -1 for sig != 0 To: cygwin@cygwin.com Content-Type: text/plain; charset=UTF-8 X-SW-Source: 2016-08/txt/msg00190.txt.bz2 Hi all, This is a followup to a report back in 2011 about essentially the same issue: https://cygwin.com/ml/cygwin/2011-04/msg00031.html The same test program in that report demonstrates the issue, but with kill sending any non-zero signal. To reiterate, the problem here is POSIX compliance with respect to sending signals to zombie processes: > Existing implementations vary on the result of a kill() with pid indicating an inactive process (a > terminated process that has not been waited for by its parent). Some indicate success on such a > call (subject to permission checking), while others give an error of [ESRCH]. Since the definition > of process lifetime in this volume of POSIX.1-2008 covers inactive processes, the [ESRCH] error > as described is inappropriate in this case. In particular, this means that an application cannot > have a parent process check for termination of a particular child with kill(). (Usually this is done > with the null signal; this can be done reliably with waitpid().) In response to the originally issue, this was fixed *specifically* for the case of kill(pid, 0). But my reading of the above is that kill() should return 0 in this case regardless of the signal (modulo permissions, etc.). On Linux, for example, when calling kill with pid of a zombie process the kernel will happily deliver the signal to the relevant task_struct; it will just never be acted on since the task will never run again. The below (untested) patch demonstrates the change I'm suggesting, though I don't know what other code, if any, might be involved in this. Please CC me on any replies since I'm not subscribed to the list. Thanks, Erik diff --git a/winsup/cygwin/signal.cc b/winsup/cygwin/signal.cc index ff101e3..d819e77 100644 --- a/winsup/cygwin/signal.cc +++ b/winsup/cygwin/signal.cc @@ -260,7 +260,7 @@ _pinfo::kill (siginfo_t& si) } this_pid = pid; } - else if (si.si_signo == 0 && this && process_state == PID_EXITED) + else if (this && process_state == PID_EXITED) { this_process_state = process_state; this_pid = pid; -- 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