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=-5.6 required=3.0 tests=BAYES_00,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 438E7C433DF for ; Tue, 11 Aug 2020 07:26:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1271520772 for ; Tue, 11 Aug 2020 07:26:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="VqcWjBvY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726543AbgHKH0u (ORCPT ); Tue, 11 Aug 2020 03:26:50 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:45177 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726667AbgHKH0u (ORCPT ); Tue, 11 Aug 2020 03:26:50 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1597130809; 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=bJqeJf5/n9PlWgEjOsiWzWBAcqP0iXDUg+uTc3v6jUA=; b=VqcWjBvYW2GWJJioTGLdUMy0DNeBbfQ+9qNUqkiflrX6poMbB9hlxaOTSrj5fYSPQvUt+V OObkGqYpdg3kSvT33gscWOS4tUGQVzTz2wJC+EMI8XsNrH6pjpPdwjh23v5daWpyza+C10 bHS7bpN/2D8O8BmMKuoVQoo/sNGA68g= 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-528-Ace1t0OjN2-y4ZXYzG2ZIQ-1; Tue, 11 Aug 2020 03:26:43 -0400 X-MC-Unique: Ace1t0OjN2-y4ZXYzG2ZIQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B3CF680047D; Tue, 11 Aug 2020 07:26:41 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.186]) by smtp.corp.redhat.com (Postfix) with SMTP id 24795100238E; Tue, 11 Aug 2020 07:26:38 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 11 Aug 2020 09:26:41 +0200 (CEST) Date: Tue, 11 Aug 2020 09:26:37 +0200 From: Oleg Nesterov To: Peter Zijlstra Cc: Jann Horn , Jens Axboe , io-uring , stable , Josef Subject: Re: [PATCH 2/2] io_uring: use TWA_SIGNAL for task_work if the task isn't running Message-ID: <20200811072637.GC21797@redhat.com> References: <03c0e282-5317-ea45-8760-2c3f56eec0c0@kernel.dk> <20200810211057.GG3982@worktop.programming.kicks-ass.net> <5628f79b-6bfb-b054-742a-282663cb2565@kernel.dk> <1629f8a9-cee0-75f1-810a-af32968c4055@kernel.dk> <20200811064516.GA21797@redhat.com> <20200811065659.GQ3982@worktop.programming.kicks-ass.net> <20200811071401.GB21797@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200811071401.GB21797@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 08/11, Oleg Nesterov wrote: > > On 08/11, Peter Zijlstra wrote: > > > > On Tue, Aug 11, 2020 at 08:45:16AM +0200, Oleg Nesterov wrote: > > > > > > ->jobctl is always modified with ->siglock held, do we really need > > > WRITE_ONCE() ? > > > > In theory, yes. The compiler doesn't know about locks, it can tear > > writes whenever it feels like it. > > Yes, but why does this matter? Could you spell please? Do you mean that compiler can temporary set/clear JOBCTL_TASK_WORK when it sets/clears another bit? Oleg.