From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from simark.ca by simark.ca with LMTP id 5g5+Lsdmb2C5GwAAWB0awg (envelope-from ) for ; Thu, 08 Apr 2021 16:25:43 -0400 Received: by simark.ca (Postfix, from userid 112) id AFE3A1EE0E; Thu, 8 Apr 2021 16:25:43 -0400 (EDT) X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on simark.ca X-Spam-Level: X-Spam-Status: No, score=-0.7 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_MSPIKE_H2,RDNS_DYNAMIC, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (ip-8-43-85-97.sourceware.org [8.43.85.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by simark.ca (Postfix) with ESMTPS id E1E041E590 for ; Thu, 8 Apr 2021 16:25:42 -0400 (EDT) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 44D1E3954801; Thu, 8 Apr 2021 20:25:42 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 44D1E3954801 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1617913542; bh=YPLzk5j7NdGoT0q5JP0SA6hUxJTC638zwg/b9hCDu94=; h=To:Subject:Date:References:In-Reply-To:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To: From; b=KdA/KQtwrl4EfJS4Bu4SxfmK5KKC6wEEqSIzRzNmIaBkbXkV0RIZmKYWlde+i+kA6 tsU8D6F60rqCKxJmTSfwG+7Ke8azNYiLwfY0ll8a/tBNPbXMwigPUkRta2u9WV/MfP sW3Y6AEWxDE3OHS5S3N5HvI96RgpiTU1gQtfo8Xw= Received: from smtp0.epfl.ch (smtp0.epfl.ch [IPv6:2001:620:618:1e0:1:80b2:e058:1]) by sourceware.org (Postfix) with ESMTPS id 2C4EB3857033 for ; Thu, 8 Apr 2021 20:25:38 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 2C4EB3857033 Received: (qmail 12748 invoked by uid 107); 8 Apr 2021 20:25:35 -0000 Received: from ax-snat-224-5.epfl.ch (HELO ewa01.intranet.epfl.ch) (192.168.224.5) (TLS, AES256-GCM-SHA384 cipher) by mail.epfl.ch (AngelmatoPhylax SMTP proxy) with ESMTPS; Thu, 08 Apr 2021 22:25:35 +0200 X-EPFL-Auth: eNaaVJdQYAD5qg1pjbVJ7zPVnFMGviy4EiE58AA8kLtfnBJUXAA= Received: from ewa09.intranet.epfl.ch (128.178.224.180) by ewa01.intranet.epfl.ch (128.178.224.158) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2106.2; Thu, 8 Apr 2021 22:25:35 +0200 Received: from ewa09.intranet.epfl.ch ([fe80::54e3:30e0:8e77:c430]) by ewa09.intranet.epfl.ch ([fe80::54e3:30e0:8e77:c430%3]) with mapi id 15.01.2106.013; Thu, 8 Apr 2021 22:25:34 +0200 To: "gdb-patches@sourceware.org" , Simon Marchi Subject: [PATCH] was Re: [PATCH 2/3] [delete] Not-so-harmless spurious call to `wait4` Thread-Topic: [PATCH] was Re: [PATCH 2/3] [delete] Not-so-harmless spurious call to `wait4` Thread-Index: AQHXLK0l+7Arifjnz0SNeRtW7B1Mgaqq78YA Date: Thu, 8 Apr 2021 20:25:34 +0000 Message-ID: <133F84AF-3B74-47B1-BEA2-830151901ADE@epfl.ch> References: <20210408191449.27434-1-dominique.quatravaux@epfl.ch> <20210408191449.27434-2-dominique.quatravaux@epfl.ch> In-Reply-To: Accept-Language: fr-CH, en-US, fr-FR Content-Language: en-US X-MS-Has-Attach: yes X-MS-TNEF-Correlator: x-originating-ip: [128.179.253.187] Content-Type: multipart/signed; boundary="Apple-Mail=_6E3AE4C1-4288-4CAA-970C-FD1FF7895F96"; protocol="application/pkcs7-signature"; micalg=sha-256 MIME-Version: 1.0 X-Content-Filtered-By: Mailman/MimeDel 2.1.29 X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Dominique Quatravaux via Gdb-patches Reply-To: Dominique Quatravaux Errors-To: gdb-patches-bounces@sourceware.org Sender: "Gdb-patches" --Apple-Mail=_6E3AE4C1-4288-4CAA-970C-FD1FF7895F96 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 > Le 8 avr. 2021 =C3=A0 21:26, Simon Marchi a = =C3=A9crit : >=20 > Can you please explain in the commit message what harm > that wait4 call does and why we want to remove it? In trying to make a better case in the commit message, I found that = swapping the two patches around made more sense. Here is an updated, = rebased, single patch (working under the assumption that the other two = will be merged first): =46rom 5c3756e9eb0342b1a5a23bcb54d5b8317743ce0d Mon Sep 17 00:00:00 2001 From: Dominique Quatravaux Date: Thu, 8 Apr 2021 21:35:57 +0200 Subject: [PATCH] [delete] not-so-harmless spurious call to `wait4` MIME-Version: 1.0 Content-Type: text/plain; charset=3DUTF-8 Content-Transfer-Encoding: 8bit As seen in https://sourceware.org/bugzilla/show_bug.cgi?id=3D24069 this code will typically wait4() a second time on the same process that was already wait4()'d a few lines above. While this used to be harmless/idempotent (when we assumed that the process already exited), this now causes a deadlock in the WIFSTOPPED case. The early (~2019) history of bug #24069 cautiously suggests to use WNOHANG instead of outright deleting the call. However, tests on the current version of Darwin (Big Sur) demonstrate that gdb runs just fine without a redundant call to wait4(), as would be expected. Notwithstanding the debatable value of conserving bug compatibility with an OS release that is more than a decade old, there is scant evidence of what that double-wait4() was supposed to achieve in the first place - A cursory investigation with `git blame` pinpoints commits bb00b29d7802 and a80b95ba67e2 from the 2008-2009 era, but fails to answer the =E2=80=9Cwhy=E2=80=9D question conclusively. --- gdb/darwin-nat.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/gdb/darwin-nat.c b/gdb/darwin-nat.c index d3edcdf3a74..ac19d330ffb 100644 --- a/gdb/darwin-nat.c +++ b/gdb/darwin-nat.c @@ -1113,9 +1113,6 @@ darwin_nat_target::decode_message = (mach_msg_header_t *hdr, res_pid, status->value.sig); } =20 - /* Looks necessary on Leopard and harmless... */ - wait4 (inf->pid, &wstatus, 0, NULL); - return ptid_t (inf->pid); } else --=20 2.31.1 =E2=80=94=20 Dominique Quatravaux +41 21 69 35624 --Apple-Mail=_6E3AE4C1-4288-4CAA-970C-FD1FF7895F96 Content-Disposition: attachment; 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