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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 8264AC2D0DB for ; Thu, 23 Jan 2020 18:08:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 55BC121569 for ; Thu, 23 Jan 2020 18:08:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579802937; bh=0qAN23vYTD70snlLDU2l54H0Kea+680fyrIrNvszBqE=; h=From:To:Cc:Subject:Date:List-ID:From; b=Z7V1maxtiaDf0kAeXENfC3LumQS03tVt+ba3WDoLHeQnEoSoyW5qysJkFrIsD0oau 4sJp8Jcs9Drqh4c82TaMP/HktfXKFT7r+3FxEOTSscIudKVQg5WspaOt7HXIBN1Q8B kchmJEJUqtLzh0fu/EVgBKBks5NcCWn3gcouLM2g= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728984AbgAWSI4 (ORCPT ); Thu, 23 Jan 2020 13:08:56 -0500 Received: from mail.kernel.org ([198.145.29.99]:57938 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727278AbgAWSI4 (ORCPT ); Thu, 23 Jan 2020 13:08:56 -0500 Received: from lenoir.home (lfbn-ncy-1-150-155.w83-194.abo.wanadoo.fr [83.194.232.155]) (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 6DF362077C; Thu, 23 Jan 2020 18:08:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579802935; bh=0qAN23vYTD70snlLDU2l54H0Kea+680fyrIrNvszBqE=; h=From:To:Cc:Subject:Date:From; b=Q70eGchcrm5DkAXfYN072iB9Cg7HgKYHIWM0kqe7Zsw+HiIXJ2TGivbwZnwFARS0j zilC41c6x1UaYpjj+0US+MlokkSM++Xy7osSrRPPbTKp6mXzGfXi5ovO3da3xnXNhF Ay+J3t5ZRm5IkcD1wa0ze9pqe7fhY9tWAz4nzRjo= From: Frederic Weisbecker To: Ingo Molnar , Peter Zijlstra Cc: LKML , Chris Wilson , Frederic Weisbecker Subject: [PATCH] sched/vtime: Prevent unstable evaluation of WARN(vtime->state) Date: Thu, 23 Jan 2020 19:08:49 +0100 Message-Id: <20200123180849.28486-1-frederic@kernel.org> X-Mailer: git-send-email 2.25.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Chris Wilson 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. Fixes: 74722bb223d0 ("sched/vtime: Bring up complete kcpustat accessor") Signed-off-by: Chris Wilson Cc: Peter Zijlstra Cc: Ingo Molnar Signed-off-by: Frederic Weisbecker --- 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 d43318a489f2..df3577149d2e 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) -- 2.25.0