From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS17314 8.43.84.0/22 X-Spam-Status: No, score=-3.7 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,RDNS_DYNAMIC,SPF_HELO_PASS,SPF_PASS shortcircuit=no 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 (4096 bits) server-digest SHA256) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id E081E1F8C6 for ; Thu, 26 Aug 2021 15:21:29 +0000 (UTC) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 087A33858435 for ; Thu, 26 Aug 2021 15:21:29 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 087A33858435 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1629991289; bh=89971CVPdXKTHtXR55fQDaUvEjm4w9dXLwyyjs8PkhI=; h=To:Subject:References:Date:In-Reply-To:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=MW/u26zYwspvSO7zxeONYv+icRHd868kTHWiMXQlrKhnZBIlwrquiPhlOx5mJBnlq 3ikn9lELYxtC4NnVEDuTYPPNWPFsp/C+REZtyvrjtCJlny2zwTbc58+gdO2uA4P9S4 ueoDbhilAj2c6VCL3PCP+c5cw2eWRMJ8Im4CllUg= 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 C37DD3858D3C for ; Thu, 26 Aug 2021 15:21:08 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org C37DD3858D3C 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-471-j9CgQUrWNkyD6mzkx3FzwA-1; Thu, 26 Aug 2021 11:21:07 -0400 X-MC-Unique: j9CgQUrWNkyD6mzkx3FzwA-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 057E21008064; Thu, 26 Aug 2021 15:21:06 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.194.140]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 26AC760877; Thu, 26 Aug 2021 15:21:04 +0000 (UTC) To: Adhemerval Zanella Subject: Re: [PATCH v2 05/19] nptl: Move setxid flag out of cancelhandling References: <20210823195047.543237-1-adhemerval.zanella@linaro.org> <20210823195047.543237-6-adhemerval.zanella@linaro.org> <87tujc783g.fsf@oldenburg.str.redhat.com> Date: Thu, 26 Aug 2021 17:21:03 +0200 In-Reply-To: (Adhemerval Zanella's message of "Thu, 26 Aug 2021 12:11:34 -0300") Message-ID: <87o89k44gw.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-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: , From: Florian Weimer via Libc-alpha Reply-To: Florian Weimer Cc: libc-alpha@sourceware.org Errors-To: libc-alpha-bounces+e=80x24.org@sourceware.org Sender: "Libc-alpha" * Adhemerval Zanella: > On 26/08/2021 08:34, Florian Weimer wrote: >> * Adhemerval Zanella: >> >>> Now that the thread state is tracked by 'joinstate' field, there is no >>> need to keep the setxid flag within the 'cancelhandling'. It simplifies >>> the atomic code to set and reset it (since there is no need to handle >>> the thread state concurrent update). >> >> Some of this functionality reimplements the tidlock. >> >> There is some functionality around thread creation, but I do not know if >> the synchronization is entirely correct. This makes it rather difficult >> to review changes. >> >> It's also not clear to me if we need to do anything to prevent early >> setxid calls: >> >>> /* Don't allow setxid until cloned. */ >> >> I suspect this should just look at the TID instead. We create the >> thread with all signals blocked, so once there is a TID (and the thread >> has not exited), it is safe to send the signal. > > I agree that we might improve the setxid code, however what I intended > with this changes is to keep its semantic as-is and just decouple it > from cancelhandling. I might revise it on a later patch to follow your > suggestions. I wonder if there is a new race here: @@ -109,41 +100,23 @@ setxid_mark_thread (struct xid_command *cmdp, struct pthread *t) /* Don't let the thread exit before the setxid handler runs. */ t->setxid_futex = 0; + /* If thread is exiting right now, ignore it. */ + if (atomic_load_acquire (&t->joinstate) == THREAD_STATE_EXITING) + return; + /* Release the futex if there is no other setxid in progress. */ + if (atomic_exchange_acquire (&t->setxid_flag, 1) == 0) + { + t->setxid_futex = 1; + futex_wake (&t->setxid_futex, 1, FUTEX_PRIVATE); } That is, if the setxid-sending thread can now wait for a futex wake that never comes. There's also a use of atomic_exchange_release whose result is not used: + atomic_exchange_release (&t->setxid_flag, 0); That should probably be store. Thanks, Florian