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,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 EFAA0C433E0 for ; Wed, 1 Jul 2020 01:11:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B623820781 for ; Wed, 1 Jul 2020 01:11:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593565871; bh=R+CWRWxBdgS789CBMsWjf9pbxc6lgAm7ICA8umueBE0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=cZX4vTj5VvOCx7o8KWumXABZ2zX6+y0ypzpdmp03mLMlXpbSjrmKy4sx7yOrlE9tW KPPxBKXdZL2ITIPQjQzT+E5VihAxiK8odngaYB5apiFJnt8BgmFaXyBQQnmmlQxNwd fGxYreJ/mXeh/iK9Q3WN7vTXDnYCKYNCcdIsQwcc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726336AbgGABKl (ORCPT ); Tue, 30 Jun 2020 21:10:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:56846 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726114AbgGABKi (ORCPT ); Tue, 30 Jun 2020 21:10:38 -0400 Received: from lenoir.home (lfbn-ncy-1-996-218.w90-101.abo.wanadoo.fr [90.101.73.218]) (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 820BD20780; Wed, 1 Jul 2020 01:10:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593565837; bh=R+CWRWxBdgS789CBMsWjf9pbxc6lgAm7ICA8umueBE0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=qUcDog9BnsFUNsBklcERwb/RghMXgW32y9k4yslt55zQpHYGouEz/aXaCWtce6ARs ngVpx6oqm9qoD5Pyta8EWHQkFF00MRz/b5ET7qoJoAmV9H8KMdkV4X4BOpKFCAlwtP EvRaIuT6IaepEdph6deD3H5lidtI5oqBnRocllyI= From: Frederic Weisbecker To: Thomas Gleixner Cc: LKML , Frederic Weisbecker , Anna-Maria Gleixner , Peter Zijlstra , Juri Lelli Subject: [RFC PATCH 01/10] timer: Prevent base->clk from moving backward Date: Wed, 1 Jul 2020 03:10:21 +0200 Message-Id: <20200701011030.14324-2-frederic@kernel.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200701011030.14324-1-frederic@kernel.org> References: <20200701011030.14324-1-frederic@kernel.org> 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 When a timer is enqueued with a negative delta (ie: expiry is below base->clk), it gets added to the wheel as expiring now (base->clk). Yet the value that gets stored in base->next_expiry, while calling trigger_dyntick_cpu(), is the initial timer->expires value. The resulting state becomes: base->next_expiry < base->clk On the next timer enqueue, forward_timer_base() may accidentally rewind base->clk. As a possible outcome, timers may expire way too early, the worst case being that the highest wheel levels get spuriously processed again. To prevent from that, make sure that base->next_expiry doesn't get below base->clk. Signed-off-by: Frederic Weisbecker Cc: Peter Zijlstra Cc: Anna-Maria Gleixner Cc: Juri Lelli --- kernel/time/timer.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 398e6eadb861..9a838d38dbe6 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -584,7 +584,15 @@ trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer) * Set the next expiry time and kick the CPU so it can reevaluate the * wheel: */ - base->next_expiry = timer->expires; + if (time_before(timer->expires, base->clk)) { + /* + * Prevent from forward_timer_base() moving the base->clk + * backward + */ + base->next_expiry = base->clk; + } else { + base->next_expiry = timer->expires; + } wake_up_nohz_cpu(base->cpu); } @@ -896,10 +904,13 @@ static inline void forward_timer_base(struct timer_base *base) * If the next expiry value is > jiffies, then we fast forward to * jiffies otherwise we forward to the next expiry value. */ - if (time_after(base->next_expiry, jnow)) + if (time_after(base->next_expiry, jnow)) { base->clk = jnow; - else + } else { + if (WARN_ON_ONCE(time_before(base->next_expiry, base->clk))) + return; base->clk = base->next_expiry; + } #endif } -- 2.26.2