From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.105 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794394440; b=vlpYsYGDYJJisfTqmKpXU70tpkCPaCacw9hIY+DB9uoGc+5nB99ayfmjCLC6MCE5DHSY mSjePLnjGWFK/4mHE85gGZ1tOG9tzrw9EMF6y1O1ZdByCU9iYlO8Oz+ww/uBqiAy7bHr3 vOcOOYVYz3sMF/Q1IHHaK6tJFSehnO9UUtZU8jyLKhPWIAzHmm5PcmmXIWFhPAV8Nr3rX FLtuNYngMkiKnGF5k5/EbgeKp7uxEH46aLz7qgTXlVJfd/vtprADL/h105wdzDI80w7n4 tfNhgVG123XhDxO3VhRMajDYvzxa2rIAsNozsBJ+REP7dZ1Hh1tYYIukkQFRRLJeHlw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794394440; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:Content-Language:From:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=Cn3ktTNbkDjmuL/zHJ/rjWGXkd/AXBHaRbLAVh2iNbY=; b=oyb3Lhyj4QwnuSrYm/AQURGaq1+pJrqCDEsaz8ILQrzj/Oze6OIYevwdze4x5nkpdS+V ag7Y+v+ccunSs363siiFRIUW5w8TctIqwlXiMK4IfJo0T0xE7scWMtWIa1TfXHBLxN8eJ 5SRgmKbd+f0B+PWL5UEZeQipOtuF2AkAlnu++3ybTRCsvACl5T3euxI9pIjgGDvD5hitc 6NJ62KQmrWbhfiJUftnwkSMIkuPGXH9qOkWELJfWHIh0+7bXBda+p7G+fcHVOdNCGWSTr i0GiwFaEIRFUYGwb8KVG14BLm2+fFE9sDckCm4h8JKg6StARR26GbURwmvjLH46z7Wg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=iJ1FCu61; arc=none smtp.remote-ip=91.218.175.105 Received: from mta0.migadu.com (out-105.mta0.migadu.com [91.218.175.105]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0F9EA606A327 for ; Wed, 11 Nov 2026 10:53:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 0F9EA606A327 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=iJ1FCu61 X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=JhsjJycj7IJdTmr0NWylTEVWvnpPIv5RGtyr5ZSWPVQ=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1794394437; v=1; x=1794999237; b=iJ1FCu61PkVXgm/f5lOcgCWQvcXOA5AaEASA7br9SFwtYVnFOCXaRbIBIH4PRvPrw6/RpLpG lWuJSabkQPqrVFqlpuXxIuS78+flyKuMx5618tBXQHYeUh8NiZt5MVfn+7JeSqXEz8sU1qvjr5I pk3D3oCfwhqRNKrYWMKiMykY= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 1f4d43568e68746b; Wed, 11 Nov 2026 10:53:56 +0000 X-Mizu-Trace-ID: 1f4d43568e68746b X-Migadu-Flow: FLOW_OUT Message-ID: <586335c2-3c46-4723-a139-a60bd601e86b@linux.dev> Date: Wed, 11 Nov 2026 18:53:50 +0800 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 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/3] cgroup/cpuset: Allow top-level partition CPU replacement To: Ridong Chen , Waiman Long , Tejun Heo Cc: Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Shuah Khan , Mathieu Desnoyers , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Guopeng Zhang References: <20261110050324.173461-1-guopeng.zhang@linux.dev> <20261110050324.173461-3-guopeng.zhang@linux.dev> Content-Language: en-US From: Guopeng Zhang In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 在 2026/11/10 20:11, Ridong Chen 写道: > > > On 11/10/2026 1:03 PM, Guopeng Zhang wrote: >> From: Guopeng Zhang >> >> When replacing a partition's CPUs, tasks_nocpu_error() checks whether >> the parent's current effective_cpus is a subset of the new exclusive >> CPU mask. The parent mask does not yet include CPUs being returned by >> the update, so this can invalidate an otherwise valid partition. >> >> For example, on an 8-CPU system without boot isolation: >> >>    echo 2-7 > A/cpuset.cpus >>    echo isolated > A/cpuset.cpus.partition >>    echo 0-4 > A/cpuset.cpus >>    cat A/cpuset.cpus.partition >>    isolated invalid (Parent unable to distribute cpu downstream) >> >> The update should return CPUs 5-7 to the parent and leave A as a >> valid isolated partition. >> >> Skip this subset check for top_cpuset. top_cpuset_sd_nocpu() already >> accounts for returned CPUs and ensures that an active boot domain >> housekeeping CPU remains. >> >> Add a regression test for this case. >> >> Fixes: 0c7f293efc87 ("cgroup/cpuset: Add cpuset.cpus.exclusive.effective for v2") >> Signed-off-by: Guopeng Zhang > > Hi Guopeng, > > Patch 2 depends on patch 1. Skipping the cpumask_subset() check for > top_cpuset is only safe because top_cpuset_sd_nocpu() added by patch 1 > now covers it. Without patch 1, patch 2 alone would let a partition > take away all the CPUs of top_cpuset. So patch 2 can't be backported > on its own, and the two have different Fixes tags. I think it would be > better to fold patch 2 into patch 1. > Thanks for the review. That makes sense. I hadn't considered the backport implications. > Also, the fix in patch 2 seems incomplete. The same false PERR_NOCPUS > happens when the parent is a local partition, as cpumask_subset() > there doesn't take the CPUs given back by the update into account > either. On an 8-CPU system: > >     cd /sys/fs/cgroup >     echo +cpuset > cgroup.subtree_control >     mkdir A1 >     echo 1-7 > A1/cpuset.cpus >     echo root > A1/cpuset.cpus.partition >     echo +cpuset > A1/cgroup.subtree_control >     mkdir A1/A2 >     echo 3-7 > A1/A2/cpuset.cpus >     echo isolated > A1/A2/cpuset.cpus.partition >     sleep 1000 & >     echo $! > A1/cgroup.procs >     echo 1-4 > A1/A2/cpuset.cpus >     cat A1/A2/cpuset.cpus.partition >     isolated invalid (Parent unable to distribute cpu downstream) > You're right. I'll fix this in the next version. Thanks， Guopeng > A2 takes CPUs 1-2 from A1 and gives CPUs 5-7 back, so A1 still has > CPUs for its task. Instead of skipping the check for top_cpuset only, > how about making the check in tasks_nocpu_error() account for the CPUs > given back by cs for all parents? The hotplug caller would then need > to not count cs->effective_xcpus as given back, similar to what patch 3 > does for top-level partitions. >