From nobody Fri Feb 13 14:10:30 2026 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 BAA01CE7A8D for ; Sun, 24 Sep 2023 10:39:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230012AbjIXKjk (ORCPT ); Sun, 24 Sep 2023 06:39:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51508 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229720AbjIXKjh (ORCPT ); Sun, 24 Sep 2023 06:39:37 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CA0F8101; Sun, 24 Sep 2023 03:39:30 -0700 (PDT) Date: Sun, 24 Sep 2023 10:39:28 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1695551969; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=3fFN/AmPZyxtAYIiavwOmm1Y7Ev2+sV7LPtdmU9WRmw=; b=Pzq1F+jHLiratYatHH4TITwm+IVb7aXDRkwi0bSxnPOCWydJdPgj87G0aU4rHBAN5ecPbt rF0GBLDQxS8XVcduXfl8BEOTUSCKryAnQrKJC33/USfQB/AVSw5VUz4St+koxytyOzIxg7 Xvuh73ZlYSxXcb6CkxJoB4TF4Ihr1DI9s8qVFf4wg5K24l/bkCPYZTlZGuio+WNG7xeeSe Za8+Q2nTZZHMKUtNPTJB3Zcjqn26xZSklutNEuujptwTn5lKVr1cjOvSiNcLGKuj/3bdXo bM56cTDhBbsetXwyxa0id0boIdJHTR+7AsHZsPDYbD6LLT0uzG5i0eXZYjdp3A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1695551969; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=3fFN/AmPZyxtAYIiavwOmm1Y7Ev2+sV7LPtdmU9WRmw=; b=NqkoVBt3h9hpO8Gjw/SvtuZfGg5iu9nq7c8PX91CzNl2ozjfux8iaEG5eRx8ym5QVXIRfM tK/pdpRGgg2SMyAA== From: "tip-bot2 for Josh Don" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: sched/core] sched/fair: Fix warning in bandwidth distribution Cc: Josh Don , Ingo Molnar , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20230922230535.296350-2-joshdon@google.com> References: <20230922230535.296350-2-joshdon@google.com> MIME-Version: 1.0 Message-ID: <169555196835.27769.10207934409952640022.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the sched/core branch of tip: Commit-ID: 2f8c62296b6f656bbfd17e9f1fadd7478003a9d9 Gitweb: https://git.kernel.org/tip/2f8c62296b6f656bbfd17e9f1fadd7478= 003a9d9 Author: Josh Don AuthorDate: Fri, 22 Sep 2023 16:05:35 -07:00 Committer: Ingo Molnar CommitterDate: Sun, 24 Sep 2023 12:08:29 +02:00 sched/fair: Fix warning in bandwidth distribution We've observed the following warning being hit in distribute_cfs_runtime(): SCHED_WARN_ON(cfs_rq->runtime_remaining > 0) We have the following race: - CPU 0: running bandwidth distribution (distribute_cfs_runtime). Inspects the local cfs_rq and makes its runtime_remaining positive. However, we defer unthrottling the local cfs_rq until after considering all remote cfs_rq's. - CPU 1: starts running bandwidth distribution from the slack timer. When it finds the cfs_rq for CPU 0 on the throttled list, it observers the that the cfs_rq is throttled, yet is not on the CSD list, and has a positive runtime_remaining, thus triggering the warning in distribute_cfs_runtime. To fix this, we can rework the local unthrottling logic to put the local cfs_rq on a local list, so that any future bandwidth distributions will realize that the cfs_rq is about to be unthrottled. Signed-off-by: Josh Don Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20230922230535.296350-2-joshdon@google.com --- kernel/sched/fair.c | 36 +++++++++++++++++++++++++----------- 1 file changed, 25 insertions(+), 11 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 41c960e..2973173 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5741,13 +5741,13 @@ static void unthrottle_cfs_rq_async(struct cfs_rq *= cfs_rq) =20 static bool distribute_cfs_runtime(struct cfs_bandwidth *cfs_b) { - struct cfs_rq *local_unthrottle =3D NULL; int this_cpu =3D smp_processor_id(); u64 runtime, remaining =3D 1; bool throttled =3D false; - struct cfs_rq *cfs_rq; + struct cfs_rq *cfs_rq, *tmp; struct rq_flags rf; struct rq *rq; + LIST_HEAD(local_unthrottle); =20 rcu_read_lock(); list_for_each_entry_rcu(cfs_rq, &cfs_b->throttled_cfs_rq, @@ -5782,11 +5782,17 @@ static bool distribute_cfs_runtime(struct cfs_bandw= idth *cfs_b) =20 /* we check whether we're throttled above */ if (cfs_rq->runtime_remaining > 0) { - if (cpu_of(rq) !=3D this_cpu || - SCHED_WARN_ON(local_unthrottle)) + if (cpu_of(rq) !=3D this_cpu) { unthrottle_cfs_rq_async(cfs_rq); - else - local_unthrottle =3D cfs_rq; + } else { + /* + * We currently only expect to be unthrottling + * a single cfs_rq locally. + */ + SCHED_WARN_ON(!list_empty(&local_unthrottle)); + list_add_tail(&cfs_rq->throttled_csd_list, + &local_unthrottle); + } } else { throttled =3D true; } @@ -5794,15 +5800,23 @@ static bool distribute_cfs_runtime(struct cfs_bandw= idth *cfs_b) next: rq_unlock_irqrestore(rq, &rf); } - rcu_read_unlock(); =20 - if (local_unthrottle) { - rq =3D cpu_rq(this_cpu); + list_for_each_entry_safe(cfs_rq, tmp, &local_unthrottle, + throttled_csd_list) { + struct rq *rq =3D rq_of(cfs_rq); + rq_lock_irqsave(rq, &rf); - if (cfs_rq_throttled(local_unthrottle)) - unthrottle_cfs_rq(local_unthrottle); + + list_del_init(&cfs_rq->throttled_csd_list); + + if (cfs_rq_throttled(cfs_rq)) + unthrottle_cfs_rq(cfs_rq); + rq_unlock_irqrestore(rq, &rf); } + SCHED_WARN_ON(!list_empty(&local_unthrottle)); + + rcu_read_unlock(); =20 return throttled; }