From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 66B5AC04EB8 for ; Tue, 11 Dec 2018 01:29:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 241A72081F for ; Tue, 11 Dec 2018 01:29:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 241A72081F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=davemloft.net Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728844AbeLKB3O (ORCPT ); Mon, 10 Dec 2018 20:29:14 -0500 Received: from shards.monkeyblade.net ([23.128.96.9]:49920 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727276AbeLKB3N (ORCPT ); Mon, 10 Dec 2018 20:29:13 -0500 Received: from localhost (unknown [IPv6:2601:601:9f80:35cd::bf5]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) (Authenticated sender: davem-davemloft) by shards.monkeyblade.net (Postfix) with ESMTPSA id CE897100AAA08; Mon, 10 Dec 2018 17:29:12 -0800 (PST) Date: Mon, 10 Dec 2018 17:29:12 -0800 (PST) Message-Id: <20181210.172912.1960183648027850219.davem@davemloft.net> To: arnd@arndb.de Cc: tgraf@suug.ch, herbert@gondor.apana.org.au, neilb@suse.com, tom@quantonium.net, keescook@chromium.org, paulb@mellanox.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] test_rhashtable: remove semaphore usage From: David Miller In-Reply-To: <20181210211957.210189-1-arnd@arndb.de> References: <20181210211957.210189-1-arnd@arndb.de> X-Mailer: Mew version 6.8 on Emacs 26.1 Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Mon, 10 Dec 2018 17:29:13 -0800 (PST) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Arnd Bergmann Date: Mon, 10 Dec 2018 22:17:20 +0100 > This is one of only two files that initialize a semaphore to a negative > value. We don't really need the two semaphores here at all, but can do > the same thing in more conventional and more effient way, by using a > single waitqueue and an atomic thread counter. > > This gets us a little bit closer to eliminating classic semaphores from > the kernel. It also fixes a corner case where we fail to continue after > one of the threads fails to start up. > > An alternative would be to use a split kthread_create()+wake_up_process() > and completely eliminate the separate synchronization. > > Signed-off-by: Arnd Bergmann > --- > This is part of a longer, untested, series to remove semaphores > from the kernel, please review as such before applying. This looks fine to me, although it seems kinda weird how the synchronization works in that the N - 1 child threads will be awoken two times, once when child N decrements the count to zero and once when the parent decrements the count to -1 which lets us past the wait_event_interruptibel(). Nevertheless it should work just fine and I have no problems with it. Want me to apply this to net-next? Thanks.