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=-4.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 E1606C433E0 for ; Fri, 5 Jun 2020 16:15:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B96482075B for ; Fri, 5 Jun 2020 16:15:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591373735; bh=UwdpKRdlqrxAPQ+pD6xjKA3W+jwOlZ4r03LkFTrY1LA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=r+nvDXUv/vOE+XwgUF2Lqszjws1avgVnl5nOiIZzoQXjvn3hFwLmwONLYN96qnPMn bs4yykQiZVogntepV4ewVOpiAvztxrU+Rarb3FeuYjqwVGduNj+fOKfFhgOdlyuD1i TskmIg9a0V8VdmXZV3mHk/3UxqCKFo23i+JW/vv8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726265AbgFEQPf (ORCPT ); Fri, 5 Jun 2020 12:15:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:54972 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725944AbgFEQPe (ORCPT ); Fri, 5 Jun 2020 12:15:34 -0400 Received: from sol.localdomain (c-107-3-166-239.hsd1.ca.comcast.net [107.3.166.239]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 15D77206DB; Fri, 5 Jun 2020 16:15:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591373734; bh=UwdpKRdlqrxAPQ+pD6xjKA3W+jwOlZ4r03LkFTrY1LA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=zLKsDwLmu6PneMG+VwHwZGHKoOyzHO9TL8dnMZwSDzM56f4c2gTVNNn9RdcetnCyC vYZVmspRNN7G+itrwzjpyfg3EA09W5ypfcsrmNcpmucq3faJwn/+LmwwkTKW4f/NHG 5MGycP4gFgaj6ueu/XoxPOxE9/G0S+ATeGVhNFsE= Date: Fri, 5 Jun 2020 09:15:32 -0700 From: Eric Biggers To: Peter Zijlstra Cc: Guenter Roeck , tglx@linutronix.de, frederic@kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, cai@lca.pw, mgorman@techsingularity.net Subject: Re: [RFC][PATCH 7/7] sched: Replace rq::wake_list Message-ID: <20200605161532.GD1373@sol.localdomain> References: <20200526161057.531933155@infradead.org> <20200526161908.129371594@infradead.org> <20200604141837.GA179816@roeck-us.net> <20200605002433.GA148196@sol.localdomain> <20200605074154.GB2750@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200605074154.GB2750@hirez.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 05, 2020 at 09:41:54AM +0200, Peter Zijlstra wrote: > On Thu, Jun 04, 2020 at 05:24:33PM -0700, Eric Biggers wrote: > > On Thu, Jun 04, 2020 at 07:18:37AM -0700, Guenter Roeck wrote: > > > On Tue, May 26, 2020 at 06:11:04PM +0200, Peter Zijlstra wrote: > > > > The recent commit: 90b5363acd47 ("sched: Clean up scheduler_ipi()") > > > > got smp_call_function_single_async() subtly wrong. Even though it will > > > > return -EBUSY when trying to re-use a csd, that condition is not > > > > atomic and still requires external serialization. > > > > > > > > The change in ttwu_queue_remote() got this wrong. > > > > > > > > While on first reading ttwu_queue_remote() has an atomic test-and-set > > > > that appears to serialize the use, the matching 'release' is not in > > > > the right place to actually guarantee this serialization. > > > > > > > > The actual race is vs the sched_ttwu_pending() call in the idle loop; > > > > that can run the wakeup-list without consuming the CSD. > > > > > > > > Instead of trying to chain the lists, merge them. > > > > > > > > Signed-off-by: Peter Zijlstra (Intel) > > > > --- > > > ... > > > > + /* > > > > + * Assert the CSD_TYPE_TTWU layout is similar enough > > > > + * for task_struct to be on the @call_single_queue. > > > > + */ > > > > + BUILD_BUG_ON(offsetof(struct task_struct, wake_entry_type) - offsetof(struct task_struct, wake_entry) != > > > > + offsetof(struct __call_single_data, flags) - offsetof(struct __call_single_data, llist)); > > > > + > > > > > > There is no guarantee in C that > > > > > > type1 a; > > > type2 b; > > > > > > in two different data structures means that offsetof(b) - offsetof(a) > > > is the same in both data structures unless attributes such as > > > __attribute__((__packed__)) are used. > > > > > > As result, this does and will cause a variety of build errors depending > > > on the compiler version and compile flags. > > > > > > Guenter > > > > Yep, this breaks the build for me. > > -ENOCONFIG For me, the problem seems to be randstruct. To reproduce, you can use (on x86_64): make defconfig echo CONFIG_GCC_PLUGIN_RANDSTRUCT=y >> .config make olddefconfig make kernel/smp.o