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 [216.205.24.124]) by sourceware.org (Postfix) with ESMTP id DFF9438515D4 for ; Wed, 8 Sep 2021 06:20:46 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org DFF9438515D4 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-251-MdGO1ftLO4OcxSj863dgDg-1; Wed, 08 Sep 2021 02:20:45 -0400 X-MC-Unique: MdGO1ftLO4OcxSj863dgDg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7F6DC1835AD8; Wed, 8 Sep 2021 06:20:44 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.195.4]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 86D8A838D0; Wed, 8 Sep 2021 06:20:43 +0000 (UTC) From: Florian Weimer To: Justin Chen via Libc-help Cc: Justin Chen , Florian Fainelli Subject: Re: Glibc pthread_rwlock_timed*() Optimization Bug References: Date: Wed, 08 Sep 2021 08:20:41 +0200 In-Reply-To: (Justin Chen via Libc-help's message of "Tue, 7 Sep 2021 14:31:58 -0700") Message-ID: <87r1dzr3k6.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 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-6.7 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-help@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-help mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 08 Sep 2021 06:20:47 -0000 * Justin Chen via Libc-help: > It seems like the compiler is incorrectly optimizing the loop because > it is not informed that the value of __wrphase_futex can be changed in > another context, which I believe should be done with the volatile > attribute. > Does this analysis look correct? Yes, it's a bug/misfeature in our custom atomics implementation. Thanks for tracking it down. Florian