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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 73FA2C43458 for ; Mon, 29 Jun 2026 07:28:04 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 440D16B0005; Mon, 29 Jun 2026 03:28:03 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4192E6B0088; Mon, 29 Jun 2026 03:28:03 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 32EAC6B008A; Mon, 29 Jun 2026 03:28:03 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 093346B0005 for ; Mon, 29 Jun 2026 03:28:02 -0400 (EDT) Received: from smtpin21.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 7D2C31405C0 for ; Mon, 29 Jun 2026 07:28:02 +0000 (UTC) X-FDA: 84932121204.21.D66538B Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf06.hostedemail.com (Postfix) with ESMTP id BD0E218000B for ; Mon, 29 Jun 2026 07:28:00 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf06.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1782718080; b=kI2zOxLV2HiwE/ZLNI3x3CiMD88u4NlHOihhySwJF4nlXKgDy5TOAUlFA1DrY5iNFj54b4 zU8nLvoQhXnwyijoo0TyLpCn5n8IHpLmEweGwsRL4CUU5GPSy8VWNEnzDNMSzIK+aoaWkR 23rVp0072iGAetB8hGtgSpeF2dIl7sU= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1782718080; h=from:from:sender: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=9K0ZkzX+wdmwIdGa0Hqy9PfDQUOF8G3dL0/A/ACpZOQ=; b=PKIO3U/SkKaEoMLb3gdL5zQG6wCuY5i9GgK+JbggrBWaI+ATT0UDynPRNY8dqBnqnFSXvP lNl7WG6VPPkvMEd09QoiufKVKfbvJtOtNM8LBzzE0JWq1q3zPCxdi5iX8wuXPM6B5xFSy4 MrckdsdDyVjc/uLGqscbzJ1nJsuM4AE= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf06.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 31950600C8; Mon, 29 Jun 2026 07:28:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A04FF1F000E9; Mon, 29 Jun 2026 07:27:54 +0000 (UTC) Message-ID: Date: Mon, 29 Jun 2026 09:27:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed To: Andrew Morton , Farhad Alemi Cc: Waiman Long , Farhad Alemi , Gregory Price , Yury Norov , Joshua Hahn , Zi Yan , Matthew Brost , Rakie Kim , Byungchul Park , Ying Huang , Alistair Popple , Rasmus Villemoes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, stable@vger.kernel.org, Tejun Heo References: <20260627231508.74201ca47c883507be97d8c2@linux-foundation.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: BD0E218000B X-Rspam-User: X-Stat-Signature: e4rkpqwfoj1h4hxu1xdzgifhsw86catr X-HE-Tag: 1782718080-69932 X-HE-Meta: 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 OAxjMvPs /+qY7bS+k7l0cMxjG327Bcv2oh9Chn80WvjAaEuETRdG7SmtrJEfHyV7fmamBXPNVAf3DmoR5Xri7KErAqR6g4RaWQcmhygT+UzbnhU3M9enNGLqT8vajw4JFF6i5ZcrTXcT8u7HL8MY/HVaATlRGqRm5O7kT4iXCptC44jy3VXdftCL2i0tsuJdt84HIlIm/HpEfiM5pYUebinq0Na2cIqL33TTlM5N18GJ/2UlMqeTjUghPSOvd6lQzHOO0SuMyFlb+osySXkZLFuilV8NOCi1Xtw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/28/26 08:15, Andrew Morton wrote: > On Sun, 14 Jun 2026 06:25:55 -0700 Farhad Alemi wrote: > >> Creating a child cpuset where cpuset.mems is never set leads to a div/0 >> when a VMA mempolicy with MPOL_F_RELATIVE_NODES rebinds in response to a >> CPU hotplug event. >> >> Reproduction steps: >> 1) Create a cgroup w/ cpuset controls (do not set cpuset.mems) >> 2) Move the task into the child cpuset >> 3) Create a VMA mempolicy for that task with MPOL_F_RELATIVE_NODES >> 4) unplug and hotplug a cpu >> echo 0 > /sys/devices/system/cpu/cpu1/online >> echo 1 > /sys/devices/system/cpu/cpu1/online >> 5) mempolicy rebind does a div/0 in mpol_relative_nodemask on the >> call to __nodes_fold() > > Oops. > >> The cpuset code passes (cs->mems_allowed) which is not guaranteed to have >> nodes to the rebind routine. Use cs->effective_mems instead, which is >> guaranteed to have a non-empty nodemask. > > Well gee, what happened with this patch. > > I apologize for misfiling a cc:stable bugfix into my post-rc1 backlog > pile, but I got there in the end. > > I guess this is an MM patch, even though it's against > kernel/cgroup/cpuset.c. > > Nobody cc'ed Tejun. Fixed. > > David acked v1 but is being coy about the v2 patch? Yes, after the discussion, I think we should add comment similar to what I proposed. -- Cheers, David