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: AS3215 2.6.0.0/16 X-Spam-Status: No, score=-4.2 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (server2.sourceware.org [IPv6:2620:52:3:1:0:246e:9693:128c]) (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 7FD5D1F8C6 for ; Thu, 26 Aug 2021 14:23:35 +0000 (UTC) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 98DA6385843B for ; Thu, 26 Aug 2021 14:23:33 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 98DA6385843B DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1629987813; bh=0gcGk7no/Gp5s9DarvzCyvxmEjbo4QmHVUC5CZg5AfE=; 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=SHHKpiWTWubZAroCY4K0WZTIUJmOECWEKzgxjsf/ZUZiapRpMoPVEv1AdwW+C9ucu eiRzRiLNSK9CMrsHdQALDNv0TMQlNoPIMKlA4QVKdUrOJQob15nI5+OQaZFjXy+IgK FfpiqH2meFl9X7i2NVj95/ZPlEtbocfmG1SG2mmo= Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTP id 5F6243858402 for ; Thu, 26 Aug 2021 14:23:14 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 5F6243858402 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-23-vUcALZ7eMGG_dJhUWsCafw-1; Thu, 26 Aug 2021 10:23:12 -0400 X-MC-Unique: vUcALZ7eMGG_dJhUWsCafw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 558118015C7; Thu, 26 Aug 2021 14:23:11 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.194.140]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7AEA45DAA5; Thu, 26 Aug 2021 14:23:10 +0000 (UTC) To: Adhemerval Zanella Subject: Re: [PATCH v2 09/19] nptl: Fix race between pthread_kill and thread exit (bug 12889) References: <20210823195047.543237-1-adhemerval.zanella@linaro.org> <20210823195047.543237-10-adhemerval.zanella@linaro.org> Date: Thu, 26 Aug 2021 16:23:08 +0200 In-Reply-To: <20210823195047.543237-10-adhemerval.zanella@linaro.org> (Adhemerval Zanella's message of "Mon, 23 Aug 2021 16:50:37 -0300") Message-ID: <878s0o70ab.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 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable 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: > diff --git a/nptl/pthread_kill.c b/nptl/pthread_kill.c > index 5d4c86f920..63fe8c44ca 100644 > --- a/nptl/pthread_kill.c > +++ b/nptl/pthread_kill.c > @@ -26,15 +26,18 @@ __pthread_kill_internal (pthread_t threadid, int sign= o) > pid_t tid; > struct pthread *pd =3D (struct pthread *) threadid; > =20 > + /* Block all signal, since the lock is recursive and used on pthread_c= ancel > + (which should be async-signal-safe). */ > + sigset_t oldmask; > + __libc_signal_block_all (&oldmask); > + lll_lock (pd->tidlock, LLL_PRIVATE); > + > if (pd =3D=3D THREAD_SELF) > /* It is a special case to handle raise() implementation after a vfo= rk > call (which does not update the PD tid field). */ > tid =3D INLINE_SYSCALL_CALL (gettid); > else > - /* Force load of pd->tid into local variable or register. Otherwise > - if a thread exits between ESRCH test and tgkill, we might return > - EINVAL, because pd->tid would be cleared by the kernel. */ > - tid =3D atomic_forced_read (pd->tid); > + tid =3D pd->tid; > =20 > int val; > if (__glibc_likely (tid > 0)) > @@ -53,6 +56,9 @@ __pthread_kill_internal (pthread_t threadid, int signo) > as an error. */ > val =3D 0; > =20 > + lll_unlock (pd->tidlock, LLL_PRIVATE); > + __libc_signal_restore_set (&oldmask); > + > return val; > } This needs a comment explaining that *all* pending signals are delivered at the point of the __libc_signal_restore_set call. I hope that this is actually what happens in Linux; POSIX only guarantees that for one pending signal that is unblocked. The problem here is that pthread_kill (pthread_self (), =E2=80=A6) must gen= erate synchronous signal, and due to the signal-blocking, it is not immediately obvious if that's the case. If we aren't sure that all signals are flushed, we need to check for the send-signal-to-self case and avoid blocking the signal there. We don't need the tidlock for that because the running thread won't go away. Thanks, Florian