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=-9.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 0A611C10F11 for ; Wed, 24 Apr 2019 17:28:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C727F2190C for ; Wed, 24 Apr 2019 17:28:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556126918; bh=zuHTLaHRDPZ2TDoYUdtOjpSuwluLsMs/x22ZQSuIj9Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=C+o1JNPyp44JKS7ji3WIlfch6l43vFcRgcezoIifU5DA3gh/xkz+8bRv7LjhJ5KEB KiH/lAQpKCRnDWlZUr7DTWNZB9b7QWUXn/UjwBThSTAvH8Kt2EaLqbtVAgYEOrBkhA OFtray5KElG6n8uzWfnpCZmpyATrBh1LFfOKcSOA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390726AbfDXR2h (ORCPT ); Wed, 24 Apr 2019 13:28:37 -0400 Received: from mail.kernel.org ([198.145.29.99]:54838 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390719AbfDXR2e (ORCPT ); Wed, 24 Apr 2019 13:28:34 -0400 Received: from localhost (62-193-50-229.as16211.net [62.193.50.229]) (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 5EB0D21906; Wed, 24 Apr 2019 17:28:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556126913; bh=zuHTLaHRDPZ2TDoYUdtOjpSuwluLsMs/x22ZQSuIj9Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=uhEri4/45d6f4qv89nIk1PFfLNhZvZONmqKyhRI2x29MZ1XrLswZbeV440vX6ihsC Ho/rN4fWQ9FALQRilAZTZeZbr8MCqG+/R6yTtQSFisNFZlE25W4Ld7mMtV+Pha4cD9 fpmnV/rsp6tPVXYBYKdp1wZtVQlQ5jMnyemGbrEU= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Phil Auld , "Peter Zijlstra (Intel)" , Anton Blanchard , Ben Segall , Linus Torvalds , Thomas Gleixner , Ingo Molnar , Sasha Levin Subject: [PATCH 4.14 61/70] sched/fair: Limit sched_cfs_period_timer() loop to avoid hard lockup Date: Wed, 24 Apr 2019 19:10:21 +0200 Message-Id: <20190424170918.628916746@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190424170906.751869122@linuxfoundation.org> References: <20190424170906.751869122@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [ Upstream commit 2e8e19226398db8265a8e675fcc0118b9e80c9e8 ] With extremely short cfs_period_us setting on a parent task group with a large number of children the for loop in sched_cfs_period_timer() can run until the watchdog fires. There is no guarantee that the call to hrtimer_forward_now() will ever return 0. The large number of children can make do_sched_cfs_period_timer() take longer than the period. NMI watchdog: Watchdog detected hard LOCKUP on cpu 24 RIP: 0010:tg_nop+0x0/0x10 walk_tg_tree_from+0x29/0xb0 unthrottle_cfs_rq+0xe0/0x1a0 distribute_cfs_runtime+0xd3/0xf0 sched_cfs_period_timer+0xcb/0x160 ? sched_cfs_slack_timer+0xd0/0xd0 __hrtimer_run_queues+0xfb/0x270 hrtimer_interrupt+0x122/0x270 smp_apic_timer_interrupt+0x6a/0x140 apic_timer_interrupt+0xf/0x20 To prevent this we add protection to the loop that detects when the loop has run too many times and scales the period and quota up, proportionally, so that the timer can complete before then next period expires. This preserves the relative runtime quota while preventing the hard lockup. A warning is issued reporting this state and the new values. Signed-off-by: Phil Auld Signed-off-by: Peter Zijlstra (Intel) Cc: Cc: Anton Blanchard Cc: Ben Segall Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: https://lkml.kernel.org/r/20190319130005.25492-1-pauld@redhat.com Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin --- kernel/sched/fair.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 9829ede00498..a5d163903835 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4672,12 +4672,15 @@ static enum hrtimer_restart sched_cfs_slack_timer(struct hrtimer *timer) return HRTIMER_NORESTART; } +extern const u64 max_cfs_quota_period; + static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer) { struct cfs_bandwidth *cfs_b = container_of(timer, struct cfs_bandwidth, period_timer); int overrun; int idle = 0; + int count = 0; raw_spin_lock(&cfs_b->lock); for (;;) { @@ -4685,6 +4688,28 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer) if (!overrun) break; + if (++count > 3) { + u64 new, old = ktime_to_ns(cfs_b->period); + + new = (old * 147) / 128; /* ~115% */ + new = min(new, max_cfs_quota_period); + + cfs_b->period = ns_to_ktime(new); + + /* since max is 1s, this is limited to 1e9^2, which fits in u64 */ + cfs_b->quota *= new; + cfs_b->quota = div64_u64(cfs_b->quota, old); + + pr_warn_ratelimited( + "cfs_period_timer[cpu%d]: period too short, scaling up (new cfs_period_us %lld, cfs_quota_us = %lld)\n", + smp_processor_id(), + div_u64(new, NSEC_PER_USEC), + div_u64(cfs_b->quota, NSEC_PER_USEC)); + + /* reset count so we don't come right back in here */ + count = 0; + } + idle = do_sched_cfs_period_timer(cfs_b, overrun); } if (idle) -- 2.19.1