From nobody Sun Feb 8 03:57:11 2026 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 35611238D54 for ; Tue, 28 Oct 2025 03:09:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761620997; cv=none; b=A+iJzh0cj3YncUz8QZH4TegPuj3bMvnPeEt/ei23K+hSA5EIVxM+wjxIktVpeeQlh4r/6RBzW4TcBz7RpalvrJ0BcPPsMhsoZ0rUQxDmh0c6I7w6LSro2Kgdotru9E6EtGfumaElMlrfXMdlqkkRQNSKvOOjp9kNFQwEvT4ivsY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761620997; c=relaxed/simple; bh=N+JrtmaXq5IabZVvDcXwEHfgJ3+FmtLPA0ykG5De14I=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Bhl2lGZ1U3cbsAO1+Y2+qbuyPEZEzzxoM7J2b1aMsWR+zvrBE6E3j+BtCZ2vdmkX6GzyjpnBWUwLw9iVQpMbDH5w8Rtdt+c/6teecRfMGanId3mDTNmMd4hA/U0+cAX/hENtEDXYJQrGbTnjxK4WhQ3zz4yzcjF4mGpQ6SjqNYA= 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=aa2d5flj; arc=none smtp.client-ip=170.10.129.124 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="aa2d5flj" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1761620994; 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=zb7uctCA+8DACYb+CzN2IamRFlY2/R42eag8ZUqBA0k=; b=aa2d5flj/PS84cpra7RzZY2aCB9yugoUSHEJcsSdRCyNmenNTNNZ1j61Zl3nCOAOC5FKsj qHXxVZ9QogA4I6UswA1IYXQTALMXFJDlMJUSZOfIJ5bIp5dKw7c4REJFNSnRBJLIJRj6Ol BBIjm6Ucfew1szEE0gZw4uC5DuJhOOc= 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-663-mhCbpsDbPXmrAnz5ukEPgQ-1; Mon, 27 Oct 2025 23:09:49 -0400 X-MC-Unique: mhCbpsDbPXmrAnz5ukEPgQ-1 X-Mimecast-MFC-AGG-ID: mhCbpsDbPXmrAnz5ukEPgQ_1761620988 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (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 0E66B196F754; Tue, 28 Oct 2025 03:09:47 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.72.112.84]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 504931800298; Tue, 28 Oct 2025 03:09:37 +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 , Thomas Gleixner Subject: [PATCHv2 1/2] sched/deadline: Skip the deadline bandwidth check if kexec_in_progress Date: Tue, 28 Oct 2025 11:09:13 +0800 Message-ID: <20251028030914.9520-2-piliu@redhat.com> In-Reply-To: <20251028030914.9520-1-piliu@redhat.com> References: <20251028030914.9520-1-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 10.30.177.111 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 [2]. This can be reproduced by: chrt -d -T 1000000 -P 1000000 0 yes > /dev/null & kexec -e Meeting deadline bandwidth requirements is unnecessary during the kexec process. Skip DL bandwidth validation to allow kexec to proceed smoothly. [1]: https://lore.kernel.org/all/20250929133602.32462-1-piliu@redhat.com/ [2]: https://lore.kernel.org/all/3408aca5-e6c9-434a-9950-82e9147fcbba@arm.c= om/ 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 72c1f72463c75..9db6f26b6cc81 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" @@ -3484,6 +3485,12 @@ 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 From nobody Sun Feb 8 03:57:11 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 DCCC7242D72 for ; Tue, 28 Oct 2025 03:10:10 +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=1761621012; cv=none; b=gAvZXY/ngUIZPDBArjFvk1lGNZZf5RMC4sLd+TTULNqV3kQ3e/PuPeHxH5/yyUPDu/5tVokygbQcwdpkCq6Q+djdEbFeJxY7qy9z35Q9YpbnpuL/keqHGY/Neal9U2YvnKhAZ+NMHIhNU8kvLcW6mMvIcLY668m9VXZxC2a4GOc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761621012; c=relaxed/simple; bh=dNVDQAbho5sZiPSWq6KQBghularpiURV4efBWN5pKzg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=hJpia/u1dKAG6Tad+UBDdqs2aDhIEZbqVk6W0cz6IN/GfF7rT13YX8d1F2sdNYAe/FpiRECpMHhY1qVKgs38wE+BxcFfokJ7KL63thCtPG/xvNjw8cZ+vyenCv7smcOLfjanAjVfLszdq+BftK0iXpNQrawS89okYT5+Ay9AKS4= 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=d3MhKR3F; 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="d3MhKR3F" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1761621009; 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=I8WR19ZGz2+uRagsLyH/16PxuPlbDWfbpOkIs9ZyrcI=; b=d3MhKR3FG+5VEe3pBt7UTkJlQ/4WiRZYXTSaeFEJruIXnoN+tZ/KMMWTC3Ij+Qza8G1/gA h98V0dJRyI9rty7RJKGSzBsaG8EhPubNXNK3iqv72ioIILfcriweRlSNnMSdhWtGPYnZ66 7qF4DwoqIXIxn8ty2UJX8G9AMyavkNI= Received: from mx-prod-mc-03.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-300-8ksgbZnRO-WlzUfowka3Ww-1; Mon, 27 Oct 2025 23:10:07 -0400 X-MC-Unique: 8ksgbZnRO-WlzUfowka3Ww-1 X-Mimecast-MFC-AGG-ID: 8ksgbZnRO-WlzUfowka3Ww_1761621000 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E267919539BC; Tue, 28 Oct 2025 03:09:59 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.72.112.84]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id DC6F618002AD; Tue, 28 Oct 2025 03:09:47 +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 , Thomas Gleixner Subject: [PATCHv2 2/2] kernel/kexec: Stop all userspace deadline tasks Date: Tue, 28 Oct 2025 11:09:14 +0800 Message-ID: <20251028030914.9520-3-piliu@redhat.com> In-Reply-To: <20251028030914.9520-1-piliu@redhat.com> References: <20251028030914.9520-1-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 10.30.177.111 Content-Type: text/plain; charset="utf-8" Now that the deadline bandwidth check has been skipped, there is nothing to prevent CPUs from being unplugged. But as deadline tasks are crowded onto the remaining CPUs, they may starve normal tasks, especially the hotplug kthreads. As a result, the kexec process will hang indefinitely. Send SIGSTOP to all userspace deadline tasks at the beginning of kexec to allow other tasks to run as CPUs are unplugged. Signed-off-by: Pingfan Liu --- kernel/kexec_core.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c index 265de9d1ff5f5..090bb58797d12 100644 --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -1132,6 +1132,18 @@ bool kexec_load_permitted(int kexec_image_type) return true; } =20 +static void stop_user_deadline_tasks(void) +{ + struct task_struct *task; + + rcu_read_lock(); + for_each_process(task) { + if (task->policy =3D=3D SCHED_DEADLINE && task->mm) + send_sig(SIGSTOP, task, 1); + } + rcu_read_unlock(); +} + /* * Move into place and start executing a preloaded standalone * executable. If nothing was preloaded return an error. @@ -1190,6 +1202,11 @@ int kernel_kexec(void) cpu_hotplug_disable(); kexec_in_progress =3D true; cpu_hotplug_enable(); + /* + * As CPU hot-removal, the crowed deadline task may starve other + * tasks. So stop them. + */ + stop_user_deadline_tasks(); kernel_restart_prepare("kexec reboot"); migrate_to_reboot_cpu(); syscore_shutdown(); --=20 2.49.0