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 ESMTP id A9B703947424 for ; Thu, 24 Jun 2021 12:28:01 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org A9B703947424 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-212-WFPLqkmjMWyEMUptlyebig-1; Thu, 24 Jun 2021 08:28:00 -0400 X-MC-Unique: WFPLqkmjMWyEMUptlyebig-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 211EA100C663; Thu, 24 Jun 2021 12:27:59 +0000 (UTC) Received: from oldenburg.str.redhat.com (ovpn-112-228.ams2.redhat.com [10.36.112.228]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4A31F60871; Thu, 24 Jun 2021 12:27:58 +0000 (UTC) From: Florian Weimer To: Szabolcs Nagy via Libc-alpha Cc: Szabolcs Nagy Subject: Re: [PATCH v2 08/14] elf: Fix DTV gap reuse logic [BZ #27135] References: <299d28c6695cd2e76f222b0d36b17b7124c549e7.1618301209.git.szabolcs.nagy@arm.com> <878s2zlhjp.fsf@oldenburg.str.redhat.com> Date: Thu, 24 Jun 2021 14:27:56 +0200 In-Reply-To: <878s2zlhjp.fsf@oldenburg.str.redhat.com> (Florian Weimer's message of "Thu, 24 Jun 2021 11:48:26 +0200") Message-ID: <87v963jvlf.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_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 24 Jun 2021 12:28:03 -0000 * Florian Weimer: > * Szabolcs Nagy via Libc-alpha: > >> For some reason only dlopen failure caused dtv gaps to be reused. >> >> It is possible that the intent was to never reuse modids for a >> different module, but after dlopen failure all gaps are reused >> not just the ones caused by the unfinished dlopened. >> >> So the code has to handle reused modids already which seems to >> work, however the data races at thread creation and tls access >> (see bug 19329 and bug 27111) may be more severe if slots are >> reused so this is scheduled after those fixes. I think fixing >> the races are not simpler if reuse is disallowed and reuse has >> other benefits, so set GL(dl_tls_dtv_gaps) whenever entries are >> removed from the middle of the slotinfo list. The value does >> not have to be correct: incorrect true value causes the next >> modid query to do a slotinfo walk, incorrect false will leave >> gaps and new entries are added at the end. >> >> Fixes bug 27135. >> --- >> elf/dl-close.c | 6 +++++- >> elf/dl-open.c | 10 ---------- >> elf/dl-tls.c | 5 +---- >> 3 files changed, 6 insertions(+), 15 deletions(-) > > Apparently this broke GNOME Shell: > > > > I'm trying to figure out why. The bug is that if there is a gap, _dl_next_tls_modid does not update the slotinfo list to mark the modid to be returned as reserved, so multiple calls in a single dlopen operation keep returning the same modid. I'm not yet sure what the proper fix is for that. Thanks, Florian