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 3442F3858C74 for ; Thu, 8 Sep 2022 20:12:37 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 3442F3858C74 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1662667955; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to; bh=Eyoo59TUlGrzIFDjQUkBI6D82wnUfSCG/c0mfKyUSxY=; b=YaI/FWKUtcC/Tc/WRKh221sxKQZbl8cnQUg2q2zdbqdA1UZ6JSbMXG85+tVe8Z8KvKF8vy gnCtuzKQ++OTSbGWMLXekFnJMvwUaQj8CpZuIW+z9v4bzOBsRybRO+bKbt8K06gyzL/Lyl s8R6/oamAf8kIEGmbq8LnmiqviqfSGA= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-639-yLZMZSkiM02f-3HndFr1zA-1; Thu, 08 Sep 2022 16:12:32 -0400 X-MC-Unique: yLZMZSkiM02f-3HndFr1zA-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 81E06804191; Thu, 8 Sep 2022 20:12:32 +0000 (UTC) Received: from greed.delorie.com (unknown [10.22.8.19]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6C8A7492C3B; Thu, 8 Sep 2022 20:12:32 +0000 (UTC) Received: from greed.delorie.com.redhat.com (localhost [127.0.0.1]) by greed.delorie.com (8.15.2/8.15.2) with ESMTP id 288KCLlZ1435338; Thu, 8 Sep 2022 16:12:21 -0400 From: DJ Delorie To: Wilco Dijkstra Cc: libc-alpha@sourceware.org Subject: Re: [PATCH] Use C11 atomics instead of atomic_decrement(_val) In-Reply-To: Date: Thu, 08 Sep 2022 16:12:21 -0400 Message-ID: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-5.0 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: atomic_decrement returns the NEW value atomic_fetch_add_relaxed returns the OLD value Wilco Dijkstra via Libc-alpha writes: > - atomic_decrement (&__pthread_total); > + atomic_fetch_add_relaxed (&__pthread_total, -1); Ok. > - atomic_decrement (&mp_.n_mmaps); > + atomic_fetch_add_relaxed (&mp_.n_mmaps, -1); Ok. > +++ b/manual/ipc.texi > @@ -89,7 +89,7 @@ by @theglibc{}. > @c > @c Given the use atomic operations this function seems > @c to be AS-safe. It is AC-unsafe because there is still > -@c a window between atomic_decrement and the pthread_push > +@c a window between atomic_fetch_add_relaxed and the pthread_push Ok. > +++ b/manual/llio.texi > @@ -2569,7 +2569,7 @@ aiocb64}, since the LFS transparently replaces the old interface. > @c lll_lock (pd->lock) @asulock @aculock > @c atomic_fetch_add_relaxed ok > @c clone ok > -@c atomic_decrement ok > +@c atomic_fetch_add_relaxed ok Ok. > - if (atomic_decrement_val (&xidcmd->cntr) == 0) > + if (atomic_fetch_add_relaxed (&xidcmd->cntr, -1) == 1) Ok. See note at beginning for why ;-) > /* Oops, we lied for a second. */ > - atomic_decrement (&__nptl_nthreads); > + atomic_fetch_add_relaxed (&__nptl_nthreads, -1); Ok. > - if (atomic_decrement_val (&map->counter) == 0) > + if (atomic_fetch_add_relaxed (&map->counter, -1) == 1) Ok. > - if (atomic_decrement_val (&mapped->counter) == 0) > + if (atomic_fetch_add_relaxed (&mapped->counter, -1) == 1) Ok. > - if (atomic_decrement_val (&mapped->counter) == 0) > + if (atomic_fetch_add_relaxed (&mapped->counter, -1) == 1) Ok. > - if (atomic_decrement_val (&mapped->counter) == 0) > + if (atomic_fetch_add_relaxed (&mapped->counter, -1) == 1) Ok. > - if (atomic_decrement_val (&mapped->counter) == 0) > + if (atomic_fetch_add_relaxed (&mapped->counter, -1) == 1) Ok. > - if (atomic_decrement_val (&mapped->counter) == 0) > + if (atomic_fetch_add_relaxed (&mapped->counter, -1) == 1) Ok. > - if (oldval != NULL && atomic_decrement_val (&oldval->counter) == 0) > + if (oldval != NULL && atomic_fetch_add_relaxed (&oldval->counter, -1) == 1) Ok. > - if (atomic_decrement_val (&mapped->counter) == 0) > + if (atomic_fetch_add_relaxed (&mapped->counter, -1) == 1) Ok. > - if (atomic_decrement_val (&mapped->counter) == 0) > + if (atomic_fetch_add_relaxed (&mapped->counter, -1) == 1) Ok. > - if (atomic_decrement_val (&mapped->counter) == 0) > + if (atomic_fetch_add_relaxed (&mapped->counter, -1) == 1) Ok. LGTM. Reviewed-by: DJ Delorie