From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=170.10.133.124 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792639052; b=e5qrlF9tk/H3Qyx87GsU9xt1IfSAhQ4yO+FoZ/UqrgIqUJmc1WkBukCGrYIGpqulwqd/ xq0HK9ftW6zOwdZCWTrNFwdZlZD671g5+zAnQ+YZ4/ud80hdzNBzhFYSC9YP5B1YfE2yR wC4+bSV3tFseS8paYiMGInW+1XBHb2b7lQIL5apKWcmxO5ni7zOir58AcTLjn/lw4YCSt p2qJ8/pFtPSlhEKwECzX8YND0WOK/Pq6aNFcjKRAIncUJcZVQIhqyvN+6rtmGg0vL55TX ntvfwGQ71bCaNgwSzxCo0hAlO7MQem3tlmyutKK3VOTUc5TU3VIDoqyMLyTwH5dAE9Q== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792639052; h=DMARC-Filter:DKIM-Signature:Received:X-MC-Unique: X-Mimecast-MFC-AGG-ID:Received:Received:From:To:Cc:Subject:Date: Message-ID:In-Reply-To:References:MIME-Version: Content-Transfer-Encoding:X-Scanned-By; bh=Qnw0J4srQiLA5T2mT8sBLYjPGzbVS2YPDTu5qKh7uz0=; b=G0Rgq5qEdSad9kD8HNTh5ZI/Nz9zuNwqwx4Wj7rMkNrgX3bMZGj/a5xM2BJjkUGlM7Tv 5Fs3B7DFJMklHjWLJRo5rG6nr/R6Vnp5GmwVLCwSAhm5h9kEoS3o1AMcf3PRc0xkutIVc 2rvzMi9m0UDxdhzJ0333mS/5siR+UPMsr/HjNaNxO2o+p6ZOEjSLP3aslgAfVAWTXZzlS NahsDWqFJhfE8BzMtUs2nBXi85tWQYjRgKYIubG1XZ55r4opRPjrAYogovToyvClYgl1O f/duRuxy7cfthsoMZhZ9KxE6xeu5g9zSkkt4ODZz07jKqjsZRUDhPChOXbLrONWswPw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=Me7bdF4l; arc=none smtp.remote-ip=170.10.133.124 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BFBAD606A337 for ; Thu, 22 Oct 2026 03:17:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org BFBAD606A337 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, unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=Me7bdF4l DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1792639050; 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=Qnw0J4srQiLA5T2mT8sBLYjPGzbVS2YPDTu5qKh7uz0=; b=Me7bdF4lqJap3/0hWOoHCLCwHrUpC1I9lyXEVUxSofIdDhpSt8MDwCNCwWlahz7le7+495 Jjcp2z166XH98v7lj8MIODVm/GdLyFVgetj5XrlcDw+n8b/NGTHv+HH1c7zbMnbeRDc79K VG3IQbComWRGOcsTkT5n6i0lcnZXS+s= Received: from mx-prod-mc-05.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-460-z4AnmJC_Mnikx9eN9EM6cg-1; Thu, 22 Oct 2026 03:17:27 +0000 X-MC-Unique: z4AnmJC_Mnikx9eN9EM6cg-1 X-Mimecast-MFC-AGG-ID: z4AnmJC_Mnikx9eN9EM6cg_1792639045 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-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 72DE219560B8; Thu, 22 Oct 2026 03:17:25 +0000 (UTC) Received: from llong-thinkpadp16vgen1.rmtusnh.csb (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id AA67818004D2; Thu, 22 Oct 2026 03:17:23 +0000 (UTC) From: Waiman Long To: Ridong Chen , Tejun Heo , Johannes Weiner , =?UTF-8?q?Michal=20Koutn=C3=BD?= , Shuah Khan Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Guopeng Zhang , Waiman Long Subject: [PATCH-next 1/6] cgroup/cpuset: Find furthest isolated ancestor for invalidated isolated partition Date: Wed, 21 Oct 2026 23:16:38 -0400 Message-ID: <20261022031643.1351877-2-longman@redhat.com> In-Reply-To: <20261022031643.1351877-1-longman@redhat.com> References: <20261022031643.1351877-1-longman@redhat.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Commit 46b885416c27 ("cgroup/cpuset: Fix a missing isolated_cpus update in update_cpumasks_hier()") searches for the closet partition root ancestor to determine if the isolated CPUs in a to be invalidated isolation partition should be removed from isolated_cpus or not. As reported by sashiko, this method may not work when there is a deeply nested isolated partition hierarchy. For instance, Consider a nested hierarchy A0 -> A1 -> A2 -> A3 where all four are PRS_ISOLATED: A0: effective_xcpus = 0-4 A1: effective_xcpus = 1-4 A2: effective_xcpus = 2-4 A3: effective_xcpus = 3-4 When A1 shrinks its exclusive_cpus from 1-4 to 1-2, A2 will update it effective_xcpus to 2. A3 will find its closet partition root ancestor A2 and decides that its effective_xcpus 3-4 should be removed from isolated_cpus which is incorrect. Address this corner case by searching for the furthest isolated partition root ancestor instead to decide if its isolated CPUs should be returned to isolated_cpus. Fixes: 46b885416c27 ("cgroup/cpuset: Fix a missing isolated_cpus update in update_cpumasks_hier()") Signed-off-by: Waiman Long --- kernel/cgroup/cpuset.c | 36 +++++++++++++++++------------------- 1 file changed, 17 insertions(+), 19 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 585a982249ad..7ead8c3b7974 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -2156,22 +2156,20 @@ static void compute_partition_effective_cpumask(struct cpuset *cs, } /* - * ancestor_partition - Find and return the closest valid partition root ancestor + * iancestor_partition - Return furthest isolated partition root ancestor available * @cs: the current cpuset - * - * Return: The closet partition root ancestor cpuset + * Return: The furthest isolated partition root ancestor available or NULL if + * not found. */ -static struct cpuset *ancestor_partition(struct cpuset *cs) +static struct cpuset *iancestor_partition(struct cpuset *cs) { struct cpuset *ancestor = parent_cs(cs); + struct cpuset *iancestor = NULL; - /* - * The top_cpuset is always a valid partition root which will stop - * the loop if it is reached. - */ - while (!is_partition_valid(ancestor)) - ancestor = parent_cs(ancestor); - return ancestor; + for (; ancestor; ancestor = parent_cs(ancestor)) + if (ancestor->partition_root_state == PRS_ISOLATED) + iancestor = ancestor; + return iancestor; } /* @@ -2283,23 +2281,23 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp, * For a to be invalidated isolated partition, * its isolated CPUs may or may not need to be * removed from isolated_cpus depending on if - * its closest partition root ancestor is a root - * or isolated partition. With a PRS_ISOLATED - * ancestor, the CPUs are checked against its - * effective xcpus to see if any of them needed - * to be removed. + * there is a furthest isolated partition root + * ancestor available. When such a PRS_ISOLATED + * ancestor is available, the CPUs are checked + * against its effective xcpus to see if any of + * them needed to be removed. */ if (is_partition_valid(cp)) new_prs = -old_prs; if (old_prs == PRS_ISOLATED) { - struct cpuset *ancestor = ancestor_partition(cp); + struct cpuset *iancestor = iancestor_partition(cp); - if (ancestor->partition_root_state == PRS_ROOT) + if (!iancestor) del_cpus = cp->effective_xcpus; else if (cpumask_andnot(tmp->delmask, cp->effective_xcpus, - ancestor->effective_xcpus)) + iancestor->effective_xcpus)) del_cpus = tmp->delmask; if (del_cpus) { -- 2.55.0