From nobody Mon Feb 9 13:36:24 2026 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 107DE3431F0 for ; Wed, 22 Oct 2025 12:14:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761135268; cv=none; b=EHTYRWs+AOkkS61afXLpu5DC/R2b+67SmXkq/mP0D4hnqTWdaufUtGWCZ8YoRgeVga9wIJtVp415Q6bKuNn77lcHWRVrWFkhBUvBQrQqtVWAH3FKmNJUWujhrWHf5zI3xvVCAz/uxCjqLmyM/WMtaFHDDlA/djdnOWjvavQohjU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761135268; c=relaxed/simple; bh=QrL7OONpmTtsZljTHd0Qyo5LOvQrGKEBSY3RO5pbFfQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=k+rEvT45sIhi3+BGtm2PRsc8CpopcNytecilUZI2QUAhh240yTRRwhoJNkhQ6vYju96bEm+RkHmVwm4YRsf4N/+jS1kCwdmYSi6sUSZYhuUw3HBY7aXfFTL/OudM6dbg/lk8knJ01wDl2UgRocTx0TFzsH/yyW9V/W2tkqMUE9g= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=OTbpQ1dt; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="OTbpQ1dt" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1761135266; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=efuKFpXatQa3caS7HeNgDN4jbZUJUL46OQhq/PHK3n4=; b=OTbpQ1dtmXEkzjGqj6nudJqZt09aGnOdw9vApPnAOKscazEeWg3/pdR1MGx57gAfqO4bWC r5V/oR9JGOzGFb8ehhfYVl+8RGBqXEzo6vLPuuZKke+gD8qC8DmcH/zwpqgeb4gvJ2P1vc 07/ivkAT2GLwywjB82+mQ04ep2J67hw= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-198-VE1wR571MBqjaxw4FgCZSw-1; Wed, 22 Oct 2025 08:14:22 -0400 X-MC-Unique: VE1wR571MBqjaxw4FgCZSw-1 X-Mimecast-MFC-AGG-ID: VE1wR571MBqjaxw4FgCZSw_1761135261 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 743361956094; Wed, 22 Oct 2025 12:14:20 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.72.112.98]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id A1F3D180035A; Wed, 22 Oct 2025 12:14:09 +0000 (UTC) From: Pingfan Liu To: kexec@lists.infradead.org, linux-kernel@vger.kernel.org Cc: Pingfan Liu , Waiman Long , Peter Zijlstra , Juri Lelli , Pierre Gondois , Andrew Morton , Baoquan He , Ingo Molnar , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Valentin Schneider , "Rafael J. Wysocki" , Joel Granados Subject: [RFC 1/3] sched/deadline: Skip the deadline bandwidth check if kexec_in_progress Date: Wed, 22 Oct 2025 20:13:43 +0800 Message-ID: <20251022121345.23496-2-piliu@redhat.com> In-Reply-To: <20251022121345.23496-1-piliu@redhat.com> References: <20251022121345.23496-1-piliu@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Content-Type: text/plain; charset="utf-8" During discussion of the scheduler deadline bug [1], Pierre Gondois pointed out a potential issue during kexec: as CPUs are unplugged, the available DL bandwidth of the root domain gradually decreases. At some point, insufficient bandwidth triggers an overflow detection, causing CPU hot-removal to fail and kexec to hang. This can be reproduced by: chrt -d -T 1000000 -P 1000000 0 yes > /dev/null & kexec -e This patch skips the DL bandwidth check if kexec is in progress. [1]: https://lore.kernel.org/all/20250929133602.32462-1-piliu@redhat.com/ Reported-by: Pierre Gondois Closes: https://lore.kernel.org/all/3408aca5-e6c9-434a-9950-82e9147fcbba@ar= m.com/ Signed-off-by: Pingfan Liu Cc: Waiman Long Cc: Peter Zijlstra Cc: Juri Lelli Cc: Pierre Gondois Cc: Andrew Morton Cc: Baoquan He Cc: Ingo Molnar Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Steven Rostedt Cc: Valentin Schneider Cc: "Rafael J. Wysocki" Cc: Joel Granados To: kexec@lists.infradead.org To: linux-kernel@vger.kernel.org --- kernel/kexec_core.c | 6 ++++++ kernel/sched/deadline.c | 7 +++++++ 2 files changed, 13 insertions(+) diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c index 31203f0bacafa..265de9d1ff5f5 100644 --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -1183,7 +1183,13 @@ int kernel_kexec(void) } else #endif { + /* + * CPU hot-removal path refers to kexec_in_progress, it + * requires a sync to ensure no in-flight hot-removing. + */ + cpu_hotplug_disable(); kexec_in_progress =3D true; + cpu_hotplug_enable(); kernel_restart_prepare("kexec reboot"); migrate_to_reboot_cpu(); syscore_shutdown(); diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index a3a43baf4314e..cc864cc348b2c 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -18,6 +18,7 @@ =20 #include #include +#include #include #include "sched.h" #include "pelt.h" @@ -3502,6 +3503,12 @@ static int dl_bw_manage(enum dl_bw_request req, int = cpu, u64 dl_bw) =20 int dl_bw_deactivate(int cpu) { + /* + * The system is shutting down and cannot roll back. There is no point + * in keeping track of bandwidth, which may fail hotplug. + */ + if (unlikely(kexec_in_progress)) + return 0; return dl_bw_manage(dl_bw_req_deactivate, cpu, 0); } =20 --=20 2.49.0