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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0B2B3C433F5 for ; Thu, 11 Nov 2021 19:52:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D7E1560F94 for ; Thu, 11 Nov 2021 19:52:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232498AbhKKTzU (ORCPT ); Thu, 11 Nov 2021 14:55:20 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:28146 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229710AbhKKTzS (ORCPT ); Thu, 11 Nov 2021 14:55:18 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1636660348; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Rj4dBkXZNM78ldukFDcDyf4+5HD2eBVeG0uoftbTD2o=; b=jBFsqjKtlL4KqZIZIFr8MTswHHMbU0mrwBcFR+SPGUuvk42Rq1TpZw3q6vNuGPbinhhpYR IRrSuF4AL6LQBE1Q4bwtn+zwiQqmweWmAk7LZRFKM9hwU5T+6dtYlHFxsH3BIF8gQvZvBQ chitOPvreG1PvwxF3d/GYUkW9gSnRNI= 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-107-EFx1BHRqNMa-dU5aRyVqkw-1; Thu, 11 Nov 2021 14:52:25 -0500 X-MC-Unique: EFx1BHRqNMa-dU5aRyVqkw-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 8B77D18125C0; Thu, 11 Nov 2021 19:52:23 +0000 (UTC) Received: from [10.22.8.202] (unknown [10.22.8.202]) by smtp.corp.redhat.com (Postfix) with ESMTP id 261AA56A87; Thu, 11 Nov 2021 19:52:20 +0000 (UTC) Message-ID: Date: Thu, 11 Nov 2021 14:52:19 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [BUG]locking/rwsem: only clean RWSEM_FLAG_HANDOFF when already set Content-Language: en-US From: Waiman Long To: Peter Zijlstra Cc: Hillf Danton , =?UTF-8?B?6ams5oyv5Y2O?= , mingo , will , "boqun.feng" , linux-kernel References: <4fafad133b074f279dbab1aa3642e23f@xiaomi.com> <20211107090131.1535-1-hdanton@sina.com> <13d683ed-793c-b502-44ff-f28114d9386b@redhat.com> <02e118c0-2116-b806-2b48-b9c91dc847dd@redhat.com> <20211110213854.GE174703@worktop.programming.kicks-ass.net> <61735528-141c-8d77-592d-b6b8fb75ebaa@redhat.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/11/21 14:36, Waiman Long wrote: > > On 11/11/21 14:20, Peter Zijlstra wrote: >> On Thu, Nov 11, 2021 at 02:14:48PM -0500, Waiman Long wrote: >>> As for the PHASE_CHANGE name, we have to be consistent in both rwsem >>> and >>> mutex. Maybe a follow up patch if you think we should change the >>> terminology. >> Well, that's exactly the point, they do radically different things. >> Having the same name for two different things is confusing. >> >> Anyway, let me go read that patch you sent. > > My understanding of handoff is to disable optimistic spinning to let > waiters in the wait queue have an opportunity to acquire the lock. > There are difference in details on how to do that in mutex and rwsem, > though. > > BTW, I have decided that we should further simply the trylock for loop > in rwsem_down_write_slowpath() to make it easier to read. That is the > only difference in the attached v2 patch compared with the previous one. My bad, I forgot to initialize waiter.handoff_set in rwsem_down_write_slowpath(). I will send out an updated version once you have finished your review. Cheers, Longman