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,SPF_PASS,USER_AGENT_MUTT 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 ED08FC520D3 for ; Tue, 20 Nov 2018 22:40:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B18E82148E for ; Tue, 20 Nov 2018 22:40:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="YD71rVdq" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B18E82148E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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 S1726329AbeKUJLy (ORCPT ); Wed, 21 Nov 2018 04:11:54 -0500 Received: from mail.kernel.org ([198.145.29.99]:55850 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725949AbeKUJLy (ORCPT ); Wed, 21 Nov 2018 04:11:54 -0500 Received: from localhost (lfbn-ncy-1-241-207.w83-194.abo.wanadoo.fr [83.194.85.207]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9BFA321479; Tue, 20 Nov 2018 22:40:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1542753625; bh=vpj/+/rSAmjzlSpbJTV4fppoXe5kFmh4a9nXdhunc4A=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=YD71rVdqU3fr1lyw7LrpMwan44g8SsHsq6dzYwL2bKy2uhfJKdml7wqkvi1frhKLU vhWyZEpawN4iLmXSDvKT3TCyQFnZJQf9WqUAKPVyM8M6QE4md5crIgLg7wm/uqpv0z cyttrIK3Mkmqi+4K61Vl5WPJkUsqIN78Y/ExzF6g= Date: Tue, 20 Nov 2018 23:40:22 +0100 From: Frederic Weisbecker To: Peter Zijlstra Cc: LKML , Wanpeng Li , Thomas Gleixner , Yauheni Kaliuta , Ingo Molnar , Rik van Riel Subject: Re: [PATCH 20/25] sched/kcpustat: Introduce vtime-aware kcpustat accessor Message-ID: <20181120224021.GB22332@lerouge> References: <1542163569-20047-1-git-send-email-frederic@kernel.org> <1542163569-20047-21-git-send-email-frederic@kernel.org> <20181120142306.GX2131@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181120142306.GX2131@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 20, 2018 at 03:23:06PM +0100, Peter Zijlstra wrote: > On Wed, Nov 14, 2018 at 03:46:04AM +0100, Frederic Weisbecker wrote: > > > +void kcpustat_cputime(struct kernel_cpustat *kcpustat, int cpu, > > + u64 *user, u64 *nice, u64 *system, > > + u64 *guest, u64 *guest_nice) > > +{ > > + struct task_struct *curr; > > + struct vtime *vtime; > > + int err; > > + > > + if (!vtime_accounting_enabled()) { > > + kcpustat_cputime_raw(kcpustat, user, nice, > > + system, guest, guest_nice); > > + return; > > + } > > + > > + rcu_read_lock(); > > + > > + do { > > + curr = rcu_dereference(kcpustat->curr); > > Like I explained earlier; I don't think the above is correct. > task_struct is itself not RCU protected. But there is at least one put_task_struct() that is enqueued as an RCU callback on release_task(). That patchset (try to) make sure that kcpustat->curr can't be assigned beyond that point. Or did I misunderstand something?