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 4573A3889804 for ; Tue, 1 Jun 2021 09:03:29 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 4573A3889804 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-474-Cz4VLThBPNimDy04lgk9SA-1; Tue, 01 Jun 2021 05:03:27 -0400 X-MC-Unique: Cz4VLThBPNimDy04lgk9SA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id ADFF9501E3; Tue, 1 Jun 2021 09:03:26 +0000 (UTC) Received: from oldenburg.str.redhat.com (ovpn-113-228.ams2.redhat.com [10.36.113.228]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D5D75679EF; Tue, 1 Jun 2021 09:03:25 +0000 (UTC) From: Florian Weimer To: Adhemerval Zanella via Libc-alpha Subject: Re: [PATCH v2 4/9] nptl: Remove CANCELING_BITMASK References: <20210527172823.3461314-1-adhemerval.zanella@linaro.org> <20210527172823.3461314-5-adhemerval.zanella@linaro.org> Date: Tue, 01 Jun 2021 11:03:23 +0200 In-Reply-To: <20210527172823.3461314-5-adhemerval.zanella@linaro.org> (Adhemerval Zanella via Libc-alpha's message of "Thu, 27 May 2021 14:28:18 -0300") Message-ID: <87bl8q6jok.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 10.5.11.16 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=-12.7 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, 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: Tue, 01 Jun 2021 09:03:30 -0000 * Adhemerval Zanella via Libc-alpha: > The CANCELING_BITMASK is used as an optimization to avoid sending > the signal when pthread_cancel is called in a concurrent manner. > > This requires then to put both the cancellation state and type on > a shared state (cancelhandling), since 'pthread_cancel' checks > whether cancellation is enabled and asynchrnous to either cancel > itself of sending the signal. > > It also requires handle the CANCELING_BITMASK on > __pthread_disable_asynccancel, however this is incurs in the same typo: =E2=80=9Cthis is incurs=E2=80=9D > issues described on BZ#12683: the cancellation is acting even *after* =E2=80=9Cis acted upon even *after*=E2=80=9D? > the syscalls returns with user visible side-effects. > > This patch removes this optimization and simplifies the pthread > cancellation implementation: pthread_cancel now first check if typo: check =E2=86=92 checks > cancellation is already pending and if not always send a signal typo: send =E2=86=92 sends Maybe add a comma before =E2=80=9Calways=E2=80=9D. > if the target is not itself. The SIGCANCEL handler is also simpified > since there is not need to setup a CAS loop. > > It also alows to move both the cancellation state and mode out of > 'cancelhadling' (it is done in subsequent patches). typo: alows > diff --git a/nptl/pthread_cancel.c b/nptl/pthread_cancel.c > index deb404600c..8dfbcff8c3 100644 > --- a/nptl/pthread_cancel.c > +++ b/nptl/pthread_cancel.c > @@ -104,72 +87,33 @@ __pthread_cancel (pthread_t th) > =09=09 " must be installed for pthread_cancel to work\n"); > } > + > + int oldch =3D atomic_fetch_or_acquire (&pd->cancelhandling, CANCELED_B= ITMASK); > + if ((oldch & CANCELED_BITMASK) !=3D 0) > + return 0; > + > + if (pd =3D=3D THREAD_SELF) > { > + /* A single-threaded process should be able to kill itself, since = there > +=09 is nothing in the POSIX specification that says that it cannot. So > +=09 we set multiple_threads to true so that cancellation points get > +=09 executed. */ > + THREAD_SETMEM (THREAD_SELF, header.multiple_threads, 1); > #ifndef TLS_MULTIPLE_THREADS_IN_TCB > -=09__libc_multiple_threads =3D 1; > + __libc_multiple_threads =3D 1; > #endif > + > + THREAD_SETMEM (pd, result, PTHREAD_CANCELED); > + if ((oldch & CANCELTYPE_BITMASK) !=3D 0) > +=09__do_cancel (); > + return 0; > } The last part is for asynchronous self-cancel, right? Don't we have to check that cancellation is enabled, too? Thanks, Florian