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 [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 07B78384858D for ; Mon, 11 Apr 2022 14:54:41 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 07B78384858D Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-251-18qPDSfCNYezRPUZgtbKLw-1; Mon, 11 Apr 2022 10:54:38 -0400 X-MC-Unique: 18qPDSfCNYezRPUZgtbKLw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E22262A5954C; Mon, 11 Apr 2022 14:54:37 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.193.61]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0457F145B995; Mon, 11 Apr 2022 14:54:36 +0000 (UTC) From: Florian Weimer To: Adhemerval Zanella Cc: libc-alpha@sourceware.org, Aurelien Jarno Subject: Re: [PATCH] nptl: Handle spurious EINTR when thread cancellation is disabled (BZ#29029) References: <20220407132602.1689442-1-adhemerval.zanella@linaro.org> Date: Mon, 11 Apr 2022 16:54:35 +0200 In-Reply-To: <20220407132602.1689442-1-adhemerval.zanella@linaro.org> (Adhemerval Zanella's message of "Thu, 7 Apr 2022 10:26:02 -0300") Message-ID: <87y20bk6vo.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 2.85 on 10.11.54.7 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-11.3 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_NONE, TXREP, T_SCC_BODY_TEXT_LINE 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-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: Mon, 11 Apr 2022 14:54:43 -0000 * Adhemerval Zanella: > @@ -56,10 +63,29 @@ __pthread_disable_asynccancel (int oldtype) > { > + /* We cannot return when we are being canceled. Upon return the > + thread might be things which would have to be undone. The > + following loop should loop until the cancellation signal is > + delivered. */ > + while (__glibc_unlikely ((newval & (CANCELING_BITMASK | CANCELED_BITMASK)) > + == CANCELING_BITMASK)) > + { > + futex_wait_simple ((unsigned int *) &self->cancelhandling, newval, > + FUTEX_PRIVATE); > + newval = atomic_load_relaxed (&self->cancelhandling); > + } Is there no FUTEX_WAKE in the patch because futex_wait_simple already fails with EINTR once the signal finally arrives? > diff --git a/nptl/descr.h b/nptl/descr.h > index ea8aca08e6..58e3849a63 100644 > --- a/nptl/descr.h > +++ b/nptl/descr.h > @@ -279,6 +279,15 @@ struct pthread > > /* Flags determining processing of cancellation. */ > int cancelhandling; > + /* Bit set if cancellation is disabled. */ > +#define CANCELSTATE_BIT 0 > +#define CANCELSTATE_BITMASK (0x01 << CANCELSTATE_BIT) > + /* Bit set if asynchronous cancellation mode is selected. */ > +#define CANCELTYPE_BIT 1 > +#define CANCELTYPE_BITMASK (0x01 << CANCELTYPE_BIT) > + /* Bit set if canceling has been initiated. */ > +#define CANCELING_BIT 2 > +#define CANCELING_BITMASK (0x01 << CANCELING_BIT) > /* Bit set if canceled. */ > #define CANCELED_BIT 3 > #define CANCELED_BITMASK (0x01 << CANCELED_BIT) 0x01 looks like a shifted bit pattern. Maybe a plain 1 is enough? Maybe add a reference to the pthread_cancel comment explaining the need for this? > diff --git a/nptl/pthread_cancel.c b/nptl/pthread_cancel.c > index 7524c7ce4d..5aad1bab78 100644 > --- a/nptl/pthread_cancel.c > +++ b/nptl/pthread_cancel.c > @@ -92,29 +103,66 @@ __pthread_cancel (pthread_t th) > + /* Some syscalls are never restarted after being interrupted by a signal > + handler, regardless of the use of SA_RESTART (they always fail with > + EINTR). So pthread_cancel can not send SIGCANCEL unless the cancellation typo: can[]not > + is enabled and set as asynchronous (in this case the cancellation will > + be acted in the cancellation handler instead by the syscall wrapper). > + Otherwise the target thread is set as 'cancelling' (CANCELING_BITMASK) > + by atomically set 'cancelhandling' and the cancelation will be acted typo: atomically set[ting] > + uppon on next cancellation entrypoing in the target thread. */ typos: up[]on, cancellation [point] Test looks okay to me. Reviewed-by: Florian Weimer Thanks, Florian