From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id E0CA23858C52 for ; Fri, 2 Dec 2022 17:37:28 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org E0CA23858C52 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1670002648; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=kyCmukgSfgEaUF0MpCTFeLcCN0Mfl/Ixrz1/OVWkWTE=; b=dOuzmS0lraoPy3BkhMO2iaC/2FyhhDjMOaV2A2o2rSkWGwpaS9rxAZlEIMwHfomLY+VJvC pOom3fUC4ECig/9qrhloFVZnKcaMUr5//l2PubfJoiWbG+hgTckdGfLiQZmSVVJVMoDgzY Wy8GnxMWmqlheb5L5fus+E9xTGAY0wQ= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-660-QQHRD57yOBqw-eLFteQyeg-1; Fri, 02 Dec 2022 12:37:18 -0500 X-MC-Unique: QQHRD57yOBqw-eLFteQyeg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id D4ED4101A52A; Fri, 2 Dec 2022 17:37:17 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.2.16.87]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1FDEB40CA40F; Fri, 2 Dec 2022 17:37:16 +0000 (UTC) From: Florian Weimer To: Paul Wise Cc: Libc-help Subject: Re: is this a bug in glibc or readpst? References: <2cefc4fa95dd439c2581f4f06d520c004cd33708.camel@bonedaddy.net> <875yf6nj43.fsf@oldenburg.str.redhat.com> Date: Fri, 02 Dec 2022 18:37:13 +0100 In-Reply-To: (Paul Wise's message of "Thu, 24 Nov 2022 08:06:41 +0800") Message-ID: <87ilitpv06.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-4.5 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: * Paul Wise: > On Wed, 2022-11-23 at 09:57 +0100, Florian Weimer via Libc-help wrote: > >> Fork still shares the underlying file description.=C2=A0 It only duplica= tes >> the descriptors.=C2=A0 If the subprocess changes the file pointer back t= o 0, >> it will affect the original process, too.=C2=A0 This is just how file >> descriptors work. >>=20 >> Could this explain the issue? > > That does sound like what the symptoms would indicate. > > However it doesn't seem to fit, because the first thing the child > process does is call freopen(), which should in theory close the > descriptor and then create a new file descriptor and file description? > > On the other hand, the fact that using fclose()+fopen() instead of > freopen() does seem to fix the problem, seems to indicate that > freopen() is not actually successfully closing the descriptor and > thus the file pointer is shared between processes? Could you run it under strace -k, with debuginfo? Hopefully that will shed some light on the problem. Thanks, Florian