From patchwork Thu Apr 16 13:21:26 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 227567 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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, 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 40D2BC2BB85 for ; Thu, 16 Apr 2020 15:45:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2022820732 for ; Thu, 16 Apr 2020 15:45:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587051950; bh=A+KPd7DvdH0SRXYueI90IJarwFnE3747OAbItcoX4T0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=T+AZlJUex6JTd+BkVVeDpqgt4OC2BWWOiCxrOhgIt1HqGcNaskcRv2ac7qzyo0Ot4 66oqbr6PxdbeUzF7AS8mHAaPrWHD2GgeHlUqp/7fONybUxcEH/38k3kSKuInu+/AAd xE+4PTVTXDeL6Z5u8vz4TEIPV8rU/Ua+e+zHWgNw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2895144AbgDPPpt (ORCPT ); Thu, 16 Apr 2020 11:45:49 -0400 Received: from mail.kernel.org ([198.145.29.99]:46456 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2896993AbgDPNev (ORCPT ); Thu, 16 Apr 2020 09:34:51 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 CB6DC21BE5; Thu, 16 Apr 2020 13:34:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587044089; bh=A+KPd7DvdH0SRXYueI90IJarwFnE3747OAbItcoX4T0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fdyDcflt98+p3UCfgfd0dhUzN6FmkOmvggs7yUIelwBDekAN3YKrfTjwrT2K/ZpCP +sL6JI2ZSEFNR71m+BOuBszgcPNlCMU8ZJ0NKiT36dmzv+3Objv7YEWdmE5KiJJ2q3 9WJV2sL7cQufbki2aWt/mUmrwnV2kB/mBgzXxgvE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Chris Wilson , Frederic Weisbecker , "Peter Zijlstra (Intel)" , Ingo Molnar , Sasha Levin Subject: [PATCH 5.5 035/257] sched/vtime: Prevent unstable evaluation of WARN(vtime->state) Date: Thu, 16 Apr 2020 15:21:26 +0200 Message-Id: <20200416131330.348146499@linuxfoundation.org> X-Mailer: git-send-email 2.26.1 In-Reply-To: <20200416131325.891903893@linuxfoundation.org> References: <20200416131325.891903893@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Chris Wilson [ Upstream commit f1dfdab694eb3838ac26f4b73695929c07d92a33 ] As the vtime is sampled under loose seqcount protection by kcpustat, the vtime fields may change as the code flows. Where logic dictates a field has a static value, use a READ_ONCE. Signed-off-by: Chris Wilson Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Fixes: 74722bb223d0 ("sched/vtime: Bring up complete kcpustat accessor") Link: https://lkml.kernel.org/r/20200123180849.28486-1-frederic@kernel.org Signed-off-by: Sasha Levin --- kernel/sched/cputime.c | 41 ++++++++++++++++++++++------------------- 1 file changed, 22 insertions(+), 19 deletions(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index d43318a489f24..df3577149d2ed 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -912,8 +912,10 @@ void task_cputime(struct task_struct *t, u64 *utime, u64 *stime) } while (read_seqcount_retry(&vtime->seqcount, seq)); } -static int vtime_state_check(struct vtime *vtime, int cpu) +static int vtime_state_fetch(struct vtime *vtime, int cpu) { + int state = READ_ONCE(vtime->state); + /* * We raced against a context switch, fetch the * kcpustat task again. @@ -930,10 +932,10 @@ static int vtime_state_check(struct vtime *vtime, int cpu) * * Case 1) is ok but 2) is not. So wait for a safe VTIME state. */ - if (vtime->state == VTIME_INACTIVE) + if (state == VTIME_INACTIVE) return -EAGAIN; - return 0; + return state; } static u64 kcpustat_user_vtime(struct vtime *vtime) @@ -952,14 +954,15 @@ static int kcpustat_field_vtime(u64 *cpustat, { struct vtime *vtime = &tsk->vtime; unsigned int seq; - int err; do { + int state; + seq = read_seqcount_begin(&vtime->seqcount); - err = vtime_state_check(vtime, cpu); - if (err < 0) - return err; + state = vtime_state_fetch(vtime, cpu); + if (state < 0) + return state; *val = cpustat[usage]; @@ -972,7 +975,7 @@ static int kcpustat_field_vtime(u64 *cpustat, */ switch (usage) { case CPUTIME_SYSTEM: - if (vtime->state == VTIME_SYS) + if (state == VTIME_SYS) *val += vtime->stime + vtime_delta(vtime); break; case CPUTIME_USER: @@ -984,11 +987,11 @@ static int kcpustat_field_vtime(u64 *cpustat, *val += kcpustat_user_vtime(vtime); break; case CPUTIME_GUEST: - if (vtime->state == VTIME_GUEST && task_nice(tsk) <= 0) + if (state == VTIME_GUEST && task_nice(tsk) <= 0) *val += vtime->gtime + vtime_delta(vtime); break; case CPUTIME_GUEST_NICE: - if (vtime->state == VTIME_GUEST && task_nice(tsk) > 0) + if (state == VTIME_GUEST && task_nice(tsk) > 0) *val += vtime->gtime + vtime_delta(vtime); break; default: @@ -1039,23 +1042,23 @@ static int kcpustat_cpu_fetch_vtime(struct kernel_cpustat *dst, { struct vtime *vtime = &tsk->vtime; unsigned int seq; - int err; do { u64 *cpustat; u64 delta; + int state; seq = read_seqcount_begin(&vtime->seqcount); - err = vtime_state_check(vtime, cpu); - if (err < 0) - return err; + state = vtime_state_fetch(vtime, cpu); + if (state < 0) + return state; *dst = *src; cpustat = dst->cpustat; /* Task is sleeping, dead or idle, nothing to add */ - if (vtime->state < VTIME_SYS) + if (state < VTIME_SYS) continue; delta = vtime_delta(vtime); @@ -1064,15 +1067,15 @@ static int kcpustat_cpu_fetch_vtime(struct kernel_cpustat *dst, * Task runs either in user (including guest) or kernel space, * add pending nohz time to the right place. */ - if (vtime->state == VTIME_SYS) { + if (state == VTIME_SYS) { cpustat[CPUTIME_SYSTEM] += vtime->stime + delta; - } else if (vtime->state == VTIME_USER) { + } else if (state == VTIME_USER) { if (task_nice(tsk) > 0) cpustat[CPUTIME_NICE] += vtime->utime + delta; else cpustat[CPUTIME_USER] += vtime->utime + delta; } else { - WARN_ON_ONCE(vtime->state != VTIME_GUEST); + WARN_ON_ONCE(state != VTIME_GUEST); if (task_nice(tsk) > 0) { cpustat[CPUTIME_GUEST_NICE] += vtime->gtime + delta; cpustat[CPUTIME_NICE] += vtime->gtime + delta; @@ -1083,7 +1086,7 @@ static int kcpustat_cpu_fetch_vtime(struct kernel_cpustat *dst, } } while (read_seqcount_retry(&vtime->seqcount, seq)); - return err; + return 0; } void kcpustat_cpu_fetch(struct kernel_cpustat *dst, int cpu)