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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 014E5CA9ED3 for ; Mon, 4 Nov 2019 22:02:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CA382214D8 for ; Mon, 4 Nov 2019 22:02:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572904977; bh=WUYtsEowu6tUKxR++J7FijFndFCjk6G0o2q2sXvWxvY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=1qzxrqewKxkCfxJLR9VSDan082d4rKSrHHUjRgAfF0YyEnP/OY87YJYwkwLMtGNDi MmCbQ71x5DRqhQwqCuydEnArLZe5fLZs0gmS4R+LTNWIrj5C0DVv7sNDn+TxNU56gZ SET3I5GTnjCx8gKwT5GOSSg/CD4JVfQCgh+wKCXc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388313AbfKDWC4 (ORCPT ); Mon, 4 Nov 2019 17:02:56 -0500 Received: from mail.kernel.org ([198.145.29.99]:33130 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389416AbfKDWCy (ORCPT ); Mon, 4 Nov 2019 17:02:54 -0500 Received: from localhost (6.204-14-84.ripe.coltfrance.com [84.14.204.6]) (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 2ACCC205C9; Mon, 4 Nov 2019 22:02:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572904973; bh=WUYtsEowu6tUKxR++J7FijFndFCjk6G0o2q2sXvWxvY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Qp2yz9aMcYn2IoImbPC1u8pEwqNLCwi9Tscdo/7O/CyKxSr22uy/U9RELyu9lHR7I VLUvqO8Kvzek6c1iy1ASQ66GEsJPb6UIPpkFm4nUyFoGKwIUBnvC+07OIqsZ+QwSj1 0z5CS3d5WWgMlg7/S/f/KmLB5ZD5VDDzioDM8kew= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Heiko Carstens , Vasily Gorbik Subject: [PATCH 4.19 128/149] s390/idle: fix cpu idle time calculation Date: Mon, 4 Nov 2019 22:45:21 +0100 Message-Id: <20191104212145.431494357@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191104212126.090054740@linuxfoundation.org> References: <20191104212126.090054740@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Heiko Carstens commit 3d7efa4edd07be5c5c3ffa95ba63e97e070e1f3f upstream. The idle time reported in /proc/stat sometimes incorrectly contains huge values on s390. This is caused by a bug in arch_cpu_idle_time(). The kernel tries to figure out when a different cpu entered idle by accessing its per-cpu data structure. There is an ordering problem: if the remote cpu has an idle_enter value which is not zero, and an idle_exit value which is zero, it is assumed it is idle since "now". The "now" timestamp however is taken before the idle_enter value is read. Which in turn means that "now" can be smaller than idle_enter of the remote cpu. Unconditionally subtracting idle_enter from "now" can thus lead to a negative value (aka large unsigned value). Fix this by moving the get_tod_clock() invocation out of the loop. While at it also make the code a bit more readable. A similar bug also exists for show_idle_time(). Fix this is as well. Cc: Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik Signed-off-by: Greg Kroah-Hartman --- arch/s390/kernel/idle.c | 29 ++++++++++++++++++++++------- 1 file changed, 22 insertions(+), 7 deletions(-) --- a/arch/s390/kernel/idle.c +++ b/arch/s390/kernel/idle.c @@ -69,18 +69,26 @@ DEVICE_ATTR(idle_count, 0444, show_idle_ static ssize_t show_idle_time(struct device *dev, struct device_attribute *attr, char *buf) { + unsigned long long now, idle_time, idle_enter, idle_exit, in_idle; struct s390_idle_data *idle = &per_cpu(s390_idle, dev->id); - unsigned long long now, idle_time, idle_enter, idle_exit; unsigned int seq; do { - now = get_tod_clock(); seq = read_seqcount_begin(&idle->seqcount); idle_time = READ_ONCE(idle->idle_time); idle_enter = READ_ONCE(idle->clock_idle_enter); idle_exit = READ_ONCE(idle->clock_idle_exit); } while (read_seqcount_retry(&idle->seqcount, seq)); - idle_time += idle_enter ? ((idle_exit ? : now) - idle_enter) : 0; + in_idle = 0; + now = get_tod_clock(); + if (idle_enter) { + if (idle_exit) { + in_idle = idle_exit - idle_enter; + } else if (now > idle_enter) { + in_idle = now - idle_enter; + } + } + idle_time += in_idle; return sprintf(buf, "%llu\n", idle_time >> 12); } DEVICE_ATTR(idle_time_us, 0444, show_idle_time, NULL); @@ -88,17 +96,24 @@ DEVICE_ATTR(idle_time_us, 0444, show_idl u64 arch_cpu_idle_time(int cpu) { struct s390_idle_data *idle = &per_cpu(s390_idle, cpu); - unsigned long long now, idle_enter, idle_exit; + unsigned long long now, idle_enter, idle_exit, in_idle; unsigned int seq; do { - now = get_tod_clock(); seq = read_seqcount_begin(&idle->seqcount); idle_enter = READ_ONCE(idle->clock_idle_enter); idle_exit = READ_ONCE(idle->clock_idle_exit); } while (read_seqcount_retry(&idle->seqcount, seq)); - - return cputime_to_nsecs(idle_enter ? ((idle_exit ?: now) - idle_enter) : 0); + in_idle = 0; + now = get_tod_clock(); + if (idle_enter) { + if (idle_exit) { + in_idle = idle_exit - idle_enter; + } else if (now > idle_enter) { + in_idle = now - idle_enter; + } + } + return cputime_to_nsecs(in_idle); } void arch_cpu_idle_enter(void)