From mboxrd@z Thu Jan 1 00:00:00 1970 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 AC8342D1936 for ; Thu, 5 Mar 2026 19:16:32 +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=1772738194; cv=none; b=WDBLQ+Fvir9NHDknIOqLwOYfGbgGWfo42n3yIoocO6JVb3Ooc1DIA1JYxNWTiyOPX1ip95aOlTakZbjAGRkWfSy9gKnajaMNCcdR2dslv/O0CMp2PX2wApliazwgwBgZpVtLXGVNNquEjYPlalsYPa6+WS80CIij2ZV80sh2AmE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772738194; c=relaxed/simple; bh=558Ea8k86MCkNDGlGfvOHDj377jokcoY0+behIHlvNM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=luZUvvdnRCUK7ULiidkmSN+tgZMiJ3Uva1q1EptDDaXi0w/2tXCwELMyNDgelfR5xOrU3BHeIkdCkf25WeIiw1Pz/QJeCw6JqEyz+kC/LOA9yue6LvmRKkObYnXxeY/bLgCNjzPXYMR1Kltj4w493CUfH6hqwM4F9g/OSNY52dA= 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=PGH2VK+H; 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="PGH2VK+H" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1772738191; h=from:from: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=EGPFVJZmXPRxRQtePLH5HEESukRKS+ushQ2bbw2CUMQ=; b=PGH2VK+HM3/bR66TlGxPCxN6NdYF1rRJlAEAqB9J0RpLyQVHGXPDqkAA1STcooZ/6T0BQi ysyrsE+OsRXNy7QfGEEKmTB9pkl8Uk02/+c1FCC/0fLDJds5Rm14tK/dvajNi69G0ImnMi uAssNMWieEXUxWf1w543MI/aHKHb9w4= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-128-VQ3hfTccM3ewV7VTLCq-MQ-1; Thu, 05 Mar 2026 14:16:27 -0500 X-MC-Unique: VQ3hfTccM3ewV7VTLCq-MQ-1 X-Mimecast-MFC-AGG-ID: VQ3hfTccM3ewV7VTLCq-MQ_1772738185 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2C0D1180061E; Thu, 5 Mar 2026 19:16:25 +0000 (UTC) Received: from [10.22.88.171] (unknown [10.22.88.171]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 8C1A13003E9F; Thu, 5 Mar 2026 19:16:23 +0000 (UTC) Message-ID: <99dc8422-6d9f-4a5a-bc60-c6d632b01802@redhat.com> Date: Thu, 5 Mar 2026 14:16:22 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] cgroup/cpuset: Call rebuild_sched_domains() directly in hotplug To: Chen Ridong , Chen Ridong , Tejun Heo , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Frederic Weisbecker Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Jon Hunter References: <20260304184100.71015-1-longman@redhat.com> Content-Language: en-US From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 On 3/5/26 1:45 AM, Chen Ridong wrote: > > On 2026/3/5 2:41, Waiman Long wrote: >> Besides deferring the call to housekeeping_update(), commit 6df415aa46ec >> ("cgroup/cpuset: Defer housekeeping_update() calls from CPU hotplug >> to workqueue") also defers the rebuild_sched_domains() call to >> the workqueue. So a new offline CPU may still be in a sched domain >> or new online CPU not showing up in the sched domains for a short >> transition period. That could be a problem in some corner cases and >> can be the cause of a reported test failure[1]. Fix it by calling > Miss Link [1]? I thought I did. Will update it with the link. > >> rebuild_sched_domains_cpuslocked() directly in hotplug as before. If >> isolated partition invalidation or recreation is being done, the >> housekeeping_update() call to update the housekeeping cpumasks will >> still be deferred to a workqueue. >> >> In commit 3bfe47967191 ("cgroup/cpuset: Move >> housekeeping_update()/rebuild_sched_domains() together"), >> housekeeping_update() is called before rebuild_sched_domains() because >> it needs to access the HK_TYPE_DOMAIN housekeeping cpumask. That is now >> changed to use the static HK_TYPE_DOMAIN_BOOT cpumask as HK_TYPE_DOMAIN >> cpumask is now changeable at run time. As a result, we can move the >> rebuild_sched_domains() call before housekeeping_update() with >> the slight advantage that it will be done in the same cpus_read_lock >> critical section without the possibility of interference by a concurrent >> cpu hot add/remove operation. >> > Nice. > >> As it doesn't make sense to acquire cpuset_mutex/cpuset_top_mutex after >> calling housekeeping_update() and immediately release them again, move >> the cpuset_full_unlock() operation inside update_hk_sched_domains() >> and rename it to cpuset_update_sd_hk_unlock() to signify that it will >> release the full set of locks. >> >> Fixes: 6df415aa46ec ("cgroup/cpuset: Defer housekeeping_update() calls from CPU hotplug to workqueue") >> Tested-by: Jon Hunter >> Signed-off-by: Waiman Long >> --- >> kernel/cgroup/cpuset.c | 59 ++++++++++++++++++++++-------------------- >> 1 file changed, 31 insertions(+), 28 deletions(-) >> >> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c >> index 271bb99b1b9d..f7657b325490 100644 >> --- a/kernel/cgroup/cpuset.c >> +++ b/kernel/cgroup/cpuset.c >> @@ -881,7 +881,7 @@ static int generate_sched_domains(cpumask_var_t **domains, >> /* >> * Cgroup v2 doesn't support domain attributes, just set all of them >> * to SD_ATTR_INIT. Also non-isolating partition root CPUs are a >> - * subset of HK_TYPE_DOMAIN housekeeping CPUs. >> + * subset of HK_TYPE_DOMAIN_BOOT housekeeping CPUs. >> */ >> for (i = 0; i < ndoms; i++) { >> /* >> @@ -890,7 +890,7 @@ static int generate_sched_domains(cpumask_var_t **domains, >> */ >> if (!csa || csa[i] == &top_cpuset) >> cpumask_and(doms[i], top_cpuset.effective_cpus, >> - housekeeping_cpumask(HK_TYPE_DOMAIN)); >> + housekeeping_cpumask(HK_TYPE_DOMAIN_BOOT)); >> else >> cpumask_copy(doms[i], csa[i]->effective_cpus); >> if (dattr) >> @@ -1331,17 +1331,22 @@ static bool prstate_housekeeping_conflict(int prstate, struct cpumask *new_cpus) >> } >> >> /* >> - * update_hk_sched_domains - Update HK cpumasks & rebuild sched domains >> + * cpuset_update_sd_hk_unlock - Rebuild sched domains, update HK & unlock >> * >> - * Update housekeeping cpumasks and rebuild sched domains if necessary. >> - * This should be called at the end of cpuset or hotplug actions. >> + * Update housekeeping cpumasks and rebuild sched domains if necessary and >> + * then do a cpuset_full_unlock(). >> + * This should be called at the end of cpuset operation. >> */ >> -static void update_hk_sched_domains(void) >> +static void cpuset_update_sd_hk_unlock(void) >> + __releases(&cpuset_mutex) >> + __releases(&cpuset_top_mutex) >> { >> + /* force_sd_rebuild will be cleared in rebuild_sched_domains_locked() */ >> + if (force_sd_rebuild) >> + rebuild_sched_domains_locked(); >> + >> if (update_housekeeping) { >> - /* Updating HK cpumasks implies rebuild sched domains */ >> update_housekeeping = false; >> - force_sd_rebuild = true; >> cpumask_copy(isolated_hk_cpus, isolated_cpus); >> >> /* >> @@ -1352,22 +1357,19 @@ static void update_hk_sched_domains(void) >> mutex_unlock(&cpuset_mutex); >> cpus_read_unlock(); >> WARN_ON_ONCE(housekeeping_update(isolated_hk_cpus)); >> - cpus_read_lock(); >> - mutex_lock(&cpuset_mutex); >> + mutex_unlock(&cpuset_top_mutex); >> + } else { >> + cpuset_full_unlock(); >> } >> - /* force_sd_rebuild will be cleared in rebuild_sched_domains_locked() */ >> - if (force_sd_rebuild) >> - rebuild_sched_domains_locked(); >> } >> >> /* >> - * Work function to invoke update_hk_sched_domains() >> + * Work function to invoke cpuset_update_sd_hk_unlock() >> */ >> static void hk_sd_workfn(struct work_struct *work) >> { >> cpuset_full_lock(); >> - update_hk_sched_domains(); >> - cpuset_full_unlock(); >> + cpuset_update_sd_hk_unlock(); >> } >> >> /** >> @@ -3232,8 +3234,7 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of, >> >> free_cpuset(trialcs); >> out_unlock: >> - update_hk_sched_domains(); >> - cpuset_full_unlock(); >> + cpuset_update_sd_hk_unlock(); >> if (of_cft(of)->private == FILE_MEMLIST) >> schedule_flush_migrate_mm(); >> return retval ?: nbytes; >> @@ -3340,8 +3341,7 @@ static ssize_t cpuset_partition_write(struct kernfs_open_file *of, char *buf, >> cpuset_full_lock(); >> if (is_cpuset_online(cs)) >> retval = update_prstate(cs, val); >> - update_hk_sched_domains(); >> - cpuset_full_unlock(); >> + cpuset_update_sd_hk_unlock(); >> return retval ?: nbytes; >> } >> >> @@ -3515,8 +3515,7 @@ static void cpuset_css_killed(struct cgroup_subsys_state *css) >> /* Reset valid partition back to member */ >> if (is_partition_valid(cs)) >> update_prstate(cs, PRS_MEMBER); >> - update_hk_sched_domains(); >> - cpuset_full_unlock(); >> + cpuset_update_sd_hk_unlock(); >> } >> >> static void cpuset_css_free(struct cgroup_subsys_state *css) >> @@ -3925,11 +3924,13 @@ static void cpuset_handle_hotplug(void) >> rcu_read_unlock(); >> } >> >> - >> /* >> - * Queue a work to call housekeeping_update() & rebuild_sched_domains() >> - * There will be a slight delay before the HK_TYPE_DOMAIN housekeeping >> - * cpumask can correctly reflect what is in isolated_cpus. >> + * rebuild_sched_domains() will always be called directly if needed >> + * to make sure that newly added or removed CPU will be reflected in >> + * the sched domains. However, if isolated partition invalidation >> + * or recreation is being done (update_housekeeping set), a work item >> + * will be queued to call housekeeping_update() to update the >> + * corresponding housekeeping cpumasks after some slight delay. >> * >> * We rely on WORK_STRUCT_PENDING_BIT to not requeue a work item that >> * is still pending. Before the pending bit is cleared, the work data >> @@ -3938,8 +3939,10 @@ static void cpuset_handle_hotplug(void) >> * previously queued work. Since hk_sd_workfn() doesn't use the work >> * item at all, this is not a problem. >> */ >> - if (update_housekeeping || force_sd_rebuild) >> - queue_work(system_unbound_wq, &hk_sd_work); >> + if (force_sd_rebuild) >> + rebuild_sched_domains_cpuslocked(); >> + if (update_housekeeping) >> + queue_work(system_dfl_wq, &hk_sd_work); >> >> free_tmpmasks(ptmp); >> } > This means that rebuild schedule domains are decoupled from HK updates, right? Yes. > I'm wondering again whether we can do the same for changes to > cpus/partition/cpus.exclusive. If we can defer the HK update, then the > cpuset_top_mutex might no longer be necessary. > > This patch looks good to me. > > Reviewed-by: Chen Ridong > Thanks, Longman