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=-4.3 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI,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 827DD1F8C6 for ; Thu, 26 Aug 2021 09:42:40 +0000 (UTC) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 535E2385841A for ; Thu, 26 Aug 2021 09:42:39 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 535E2385841A DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1629970959; bh=vw6xEYodnHJjd1stgUHRvKugjGodWCdv+D4rhZyiMec=; 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=yKhDNEfVjThRcWTUJtw8kD0tHBzXrUcB532cny2h0mVFjZulD1BEDYtQ6hgvsc43C uyE5U+OTDdMKrclIVLes854k2zXo2FpAmvPi5cEUnFXUHfc841QTg7O19XxPvK7a8p VzGaoHrIERW+Zi1/yjk+tCbaFJvnDqbqSmYL0yb0= 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 1BA443858402 for ; Thu, 26 Aug 2021 09:42:20 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 1BA443858402 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-535-BXcP1dkbOtmeRZZxbHOIag-1; Thu, 26 Aug 2021 05:42:18 -0400 X-MC-Unique: BXcP1dkbOtmeRZZxbHOIag-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 47071CC624; Thu, 26 Aug 2021 09:42:17 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.194.140]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 78FB56A8FB; Thu, 26 Aug 2021 09:42:16 +0000 (UTC) To: Adhemerval Zanella Subject: Re: [PATCH v2 03/19] nptl: Handle robust PI mutexes for !__ASSUME_SET_ROBUST_LIST References: <20210823195047.543237-1-adhemerval.zanella@linaro.org> <20210823195047.543237-4-adhemerval.zanella@linaro.org> Date: Thu, 26 Aug 2021 11:42:14 +0200 In-Reply-To: <20210823195047.543237-4-adhemerval.zanella@linaro.org> (Adhemerval Zanella's message of "Mon, 23 Aug 2021 16:50:31 -0300") Message-ID: <87lf4o8rux.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 10.5.11.15 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: > The robust PI mutexes are signaled by setting the LSB bit to 1, so > the code requires to take this consideration before access the > __pthread_mutex_s. > > The code is also simplified: the initialization code is not really > required, PD->robust_head.list and PD->robust_list.__next are > essentially the same regardless of __PTHREAD_MUTEX_HAVE_PREV, the futex > wake is optimized to be issued only when required, and the futex shared > bit is set only when required. Is this a user-visible bug? Should it have a bug reference? > diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c > index d8ec299cb1..08e5189ad6 100644 > --- a/nptl/pthread_create.c > +++ b/nptl/pthread_create.c > @@ -486,35 +486,36 @@ start_thread (void *arg) > exit (0); > > #ifndef __ASSUME_SET_ROBUST_LIST > - /* If this thread has any robust mutexes locked, handle them now. */ > -# if __PTHREAD_MUTEX_HAVE_PREV > - void *robust = pd->robust_head.list; > -# else > - __pthread_slist_t *robust = pd->robust_list.__next; > -# endif > - /* We let the kernel do the notification if it is able to do so. > - If we have to do it here there for sure are no PI mutexes involved > - since the kernel support for them is even more recent. */ > - if (!__nptl_set_robust_list_avail > - && __builtin_expect (robust != (void *) &pd->robust_head, 0)) > + /* We let the kernel do the notification if it is able to do so on the exit > + syscall. Otherwise we need to handle before the thread terminates. */ > + void **robust; > + while ((robust = pd->robust_head.list) > + && robust != (void *) &pd->robust_head) > { > - do > + /* Note: robust PI futexes are signaled by setting bit 0. */ > + void **robustp = (void **) ((uintptr_t) robust & ~1UL); > + > + struct __pthread_mutex_s *mtx = (struct __pthread_mutex_s *) > + ((char *) robustp - offsetof (struct __pthread_mutex_s, > + __list.__next)); > + unsigned int nusers = mtx->__nusers; > + int shared = mtx->__kind & 128; > + > + pd->robust_head.list_op_pending = robust; > + pd->robust_head.list = *robustp; > + /* Although the list will not be changed at this point, it follows the > + expected kernel ABI. */ > + __asm ("" ::: "memory"); > + > + int lock = atomic_exchange_relaxed (&mtx->__lock, FUTEX_OWNER_DIED); > + /* Wake any users if mutex is acquired with potential users. */ > + if (lock > 1 || nusers != 0) Why the check for nusers? Isn't that racy? Thanks, Florian