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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4AC91EB64D9 for ; Thu, 15 Jun 2023 09:19:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238966AbjFOJTH (ORCPT ); Thu, 15 Jun 2023 05:19:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53266 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245365AbjFOJS7 (ORCPT ); Thu, 15 Jun 2023 05:18:59 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 587952948; Thu, 15 Jun 2023 02:18:39 -0700 (PDT) Date: Thu, 15 Jun 2023 11:18:30 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1686820716; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=yJBsHhi9j6gaSH/KNGHZ5dzFeRRVsQfjlw4dKP1tSb4=; b=swgDGj1M5ZGeCmNyyi7zwy4Dq1HvUfl2MBxr31zksTOwbhSdUevS1p3UpZcK3/T0MkNt1F nHuCXIzNYnfnP/6YnJLiG4VoQozYoN4mNGMXbukXzGgz6lIv0xUdF/PCbD86gYOYy8b97v QWs5YNMHwloyKSOeOV2t2ZgmUadm0RVzL84OleJTjmCkpg/uRHFrOkZVD8K4un6p6+7Rna 1fIuFa0lUPXiqGX4XfbTBRZiwjilJPPhn5KoBmU2+YQc9EHqLHhEaUCo7W50+2WVN3ANjR 3Gdda4frgMP3qGtq4lhnQiHXJc76DAQpoAz/a9dxwKPCjuZU7ESUGxYzRH3EwQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1686820716; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=yJBsHhi9j6gaSH/KNGHZ5dzFeRRVsQfjlw4dKP1tSb4=; b=gzvNSb/m65jWOeSAkle1s46pqKGz3L9mEUrGata/nSLK3nLDiOPcBF0Y/ulDp90fZHnlkQ XFo0YxdU7ZEnLUDQ== From: Sebastian Andrzej Siewior To: Mathias Krause Cc: Luiz Capitulino , Sven-Haegar Koch , "gregkh@linuxfoundation.org" , "Bhatnagar, Rishabh" , "linux-kernel@vger.kernel.org" , "tglx@linutronix.de" , "sashal@kernel.org" , abuehaze@amazon.com, "stable@vger.kernel.org" , Frederic Weisbecker , Ingo Molnar Subject: [PATCH] tick/common: Align tick period during sched_timer setup. Message-ID: <20230615091830.RxMV2xf_@linutronix.de> References: <12c6f9a3-d087-b824-0d05-0d18c9bc1bf3@amazon.com> <2023061428-compacter-economic-b648@gregkh> <20230614092045.tNY8USjq@linutronix.de> <4c4178a1-1050-ced4-e6fb-f95c3bdefc98@amazon.com> <2a3fa097-8ba0-5b0e-f506-779fee5b8fef@sdinet.de> <23fb8ad7-beb0-ae1c-fa5a-a682a57f79b0@grsecurity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <23fb8ad7-beb0-ae1c-fa5a-a682a57f79b0@grsecurity.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Thomas Gleixner The tick period is aligned very early while the first clock_event_device is registered. The system runs in periodic mode and switches later to one-shot mode if possible. The next wake-up event is programmed based on aligned value (tick_next_period) but the delta value, that is used to program the clock_event_device, is computed based on ktime_get(). With the subtracted offset, the devices fires in less than the exacted time frame. With a large enough offset the system programs the timer for the next wake-up and the remaining time left is too little to make any boot progress. The system hangs. Move the alignment later to the setup of tick_sched timer. At this point the system switches to oneshot mode and a highres clocksource is available. It safe to update tick_next_period ktime_get() will now return accurate (not jiffies based) time. [bigeasy: Patch description + testing]. Reported-by: Mathias Krause Reported-by: "Bhatnagar, Rishabh" Fixes: e9523a0d81899 ("tick/common: Align tick period with the HZ tick.") Signed-off-by: Thomas Gleixner Signed-off-by: Sebastian Andrzej Siewior Link: https://lore.kernel.org/5a56290d-806e-b9a5-f37c-f21958b5a8c0@grsecurity.net Link: https://lore.kernel.org/12c6f9a3-d087-b824-0d05-0d18c9bc1bf3@amazon.com --- kernel/time/tick-common.c | 11 +---------- kernel/time/tick-sched.c | 13 ++++++++++++- 2 files changed, 13 insertions(+), 11 deletions(-) diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index 65b8658da829e..b85f2f9c32426 100644 --- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -218,19 +218,10 @@ static void tick_setup_device(struct tick_device *td, * this cpu: */ if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) { - ktime_t next_p; - u32 rem; tick_do_timer_cpu = cpu; - next_p = ktime_get(); - div_u64_rem(next_p, TICK_NSEC, &rem); - if (rem) { - next_p -= rem; - next_p += TICK_NSEC; - } - - tick_next_period = next_p; + tick_next_period = ktime_get(); #ifdef CONFIG_NO_HZ_FULL /* * The boot CPU may be nohz_full, in which case set diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 52254679ec489..42c0be3080bde 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -161,8 +161,19 @@ static ktime_t tick_init_jiffy_update(void) raw_spin_lock(&jiffies_lock); write_seqcount_begin(&jiffies_seq); /* Did we start the jiffies update yet ? */ - if (last_jiffies_update == 0) + if (last_jiffies_update == 0) { + u32 rem; + + /* + * Ensure that the tick is aligned to a multiple of + * TICK_NSEC. + */ + div_u64_rem(tick_next_period, TICK_NSEC, &rem); + if (rem) + tick_next_period += TICK_NSEC - rem; + last_jiffies_update = tick_next_period; + } period = last_jiffies_update; write_seqcount_end(&jiffies_seq); raw_spin_unlock(&jiffies_lock); -- 2.40.1