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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 85AF7C34026 for ; Tue, 18 Feb 2020 15:07:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5B106207FD for ; Tue, 18 Feb 2020 15:07:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="STjCcx3q" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726762AbgBRPH6 (ORCPT ); Tue, 18 Feb 2020 10:07:58 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:28888 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726754AbgBRPH6 (ORCPT ); Tue, 18 Feb 2020 10:07:58 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1582038477; 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:references:references; bh=Csihf+yC5wp9Zjgw8iwbaFl0vMLJ/l7ONnGLpyNywMw=; b=STjCcx3qjplHEE4bCLXzsxspPRE7H+4gsA3fSVmZepLJpP0h6wMd5O5L/gcNuLM0KM7OPN vuzG0XLE03pXiD6z444UYq3RkYnv6DKk2MUJXO5TPIbaPaU/V7cl8DkEpAC6OhiM2awwog 9WQ1f9XemIxzt1a41IFzCoB2c7V3fm8= 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-288-a1QYYBk_NG2RvPL4vCLc8A-1; Tue, 18 Feb 2020 10:07:53 -0500 X-MC-Unique: a1QYYBk_NG2RvPL4vCLc8A-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C488F802692; Tue, 18 Feb 2020 15:07:48 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.70]) by smtp.corp.redhat.com (Postfix) with SMTP id 55E1860FFB; Tue, 18 Feb 2020 15:07:46 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 18 Feb 2020 16:07:48 +0100 (CET) Date: Tue, 18 Feb 2020 16:07:45 +0100 From: Oleg Nesterov To: Peter Zijlstra Cc: Jens Axboe , Carter Li =?utf-8?B?5p2O6YCa5rSy?= , Pavel Begunkov , io-uring Subject: Re: [ISSUE] The time cost of IOSQE_IO_LINK Message-ID: <20200218150745.GC3466@redhat.com> References: <7c4c3996-4886-eb58-cdee-fe0951907ab5@kernel.dk> <20200217120920.GQ14914@hirez.programming.kicks-ass.net> <53de3581-b902-89ba-3f53-fd46b052df40@kernel.dk> <43c066d1-a892-6a02-82e7-7be850d9454d@kernel.dk> <20200217174610.GU14897@hirez.programming.kicks-ass.net> <592cf069-41ee-0bc1-1f83-e058e5dd53ff@kernel.dk> <20200218131310.GZ14914@hirez.programming.kicks-ass.net> <20200218145645.GB3466@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200218145645.GB3466@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 02/18, Oleg Nesterov wrote: > > otherwise I think this is correct, but how about the patch below? > Then this code can be changed to use try_cmpxchg(). You have already sent the patch which adds the generic try_cmpxchg, so the patch below can be trivially adapted. But I'd prefer another change, I think both task_work_add() and task_work_cancel() can use try_cmpxchg() too. > > Oleg. > > --- a/kernel/task_work.c > +++ b/kernel/task_work.c > @@ -97,17 +97,24 @@ void task_work_run(void) > * work->func() can do task_work_add(), do not set > * work_exited unless the list is empty. > */ > - raw_spin_lock_irq(&task->pi_lock); > do { > + head = NULL; > work = READ_ONCE(task->task_works); > - head = !work && (task->flags & PF_EXITING) ? > - &work_exited : NULL; > + if (!work) { > + if (task->flags & PF_EXITING) > + head = &work_exited; > + else > + break; > + } > } while (cmpxchg(&task->task_works, work, head) != work); > - raw_spin_unlock_irq(&task->pi_lock); > > if (!work) > break; > > + // Synchronize with task_work_cancel() > + raw_spin_lock_irq(&task->pi_lock); > + raw_spin_unlock_irq(&task->pi_lock); > + > do { > next = work->next; > work->func(work);