From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.188 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793844824; b=fnVbIekca9xXwVA3l4lU/Z+JUCfikiE/7OlrG721x9AbCQXGYX0VC11zzc0A1X9+Dbx7 sOWBEklS/fUMFwJSzs8EMQYxrbd39VH5jeNcgNi6+DcvHR9B+5ikiyiy7YUqsUuqQV5xA R+Pjkmyf0HLo76V7YPy03xqYBFf3TS77zOFFOCBco4lsQuMAz8s8u2/Yqe7DA/3vRoUh9 lo9cnRAiGVIC5ywXA+hSmTM/23NnCgpqokxAPPnVfO1vbKZpPh9IoDA5Cx25yhVWq7CD+ e9qhG/pzgCc40oG3AqIa9MrUGq/3Btc4gqBvTaw8g3x2WNstsLzeheSM5CYg6wWky4w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793844824; 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:From:In-Reply-To:Content-Type: Content-Transfer-Encoding; bh=hNDLSFapUDH5zg85s2N1cWnGesB/dC3nKW1Zdod/mJM=; b=4aD0QaZNvE1pKbL8E8JkNxIahUbu0yD7rKPXzTl0QiZOkpvMD5gJQUP0HdyzABVe7wc+ 0Ph+Ka09p8k5XCJGdznoGVj5qUAcSI5bZzdtwY3HmeyWnrfMe/b8T6qRcEoIcu12fm6cB +tmgHAZ4AnRVTgfBGj+P75LezzuE0ahF2RsgKpQPAhzGgTMmVQO5qk2JXs3gseqy7e/1T dGu8GWmd8hPzppL902VViYHENf0JOd64w98QdqOGu1ZZFCawdqj041X2zrqZqHOO+PNAY Cyt0JyJZCa0HuqHg0TEpzUOmUbICQ1BrajwZUyCW+ybWAczoGi/6gmUHgtlpBUp1rwA== 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=GTN47C24; arc=none smtp.remote-ip=91.218.175.188 Received: from mta0.migadu.com (out-188.mta0.migadu.com [91.218.175.188]) (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 89584606A329 for ; Thu, 5 Nov 2026 02:13:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 89584606A329 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=GTN47C24 X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=8I/giyMs0wqeew5AfRUUOtj+4dlC5TxPYe3tjop4G7Q=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793844821; v=1; x=1794449621; b=GTN47C242OTjxoETwRoDA4BNNMBb96ebNpD8Fs7hcBOuXEfB4UY9tjCqMCMULvNYzHbZTVs9 rF0xm7EfvvrHIlO+8uqH39Q+2TJFSVheoWh0KNsIYT29D3R3Sxt3FqEfBpj54Vs8kS3zteYOtL/ UaYoLjy6PfYWWvgx9bN5zOwc= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 8fb82eb1ffacc0da; Thu, 05 Nov 2026 02:13:41 +0000 X-Mizu-Trace-ID: 8fb82eb1ffacc0da X-Migadu-Flow: FLOW_OUT Message-ID: Date: Thu, 5 Nov 2026 10:13:33 +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] cgroup/cpuset: Fail if isolated CPUs don't leave any boot domain housekeeping CPU To: Waiman Long , Guopeng Zhang Cc: tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com, shuah@kernel.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Guopeng Zhang References: <20261104071600.474587-1-guopeng.zhang@linux.dev> <21cfe1b7-be80-4f3b-8366-cd77afd113b0@redhat.com> From: Ridong Chen In-Reply-To: <21cfe1b7-be80-4f3b-8366-cd77afd113b0@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 11/5/2026 2:54 AM, Waiman Long wrote: > On 11/4/26 7:58 AM, Ridong Chen wrote: >> >> >> On 11/4/2026 3:16 PM, Guopeng Zhang wrote: >>> From: Guopeng Zhang >>> >>> With the "domain" flag of the isolcpus= boot option, the CPUs isolated >>> at boot are excluded from the sched domains and the remaining CPUs >>> become the boot domain housekeeping CPUs. An isolated partition is >>> allowed to use the boot isolated CPUs, but it must not take over all >>> the boot domain housekeeping CPUs. >>> >>> prstate_housekeeping_conflict() checks that rule for root partitions >>> only. The 2nd check covers the nohz_full case as it is gated by >>> housekeeping_enabled(HK_TYPE_KERNEL_NOISE) which is not enabled by >>> isolcpus=domain. So on an isolcpus=domain, boot, an isolated >>> partition can claim all the remaining boot domain housekeeping CPUs. >>> The state is committed, but the sched domain rebuild at the end of >>> the write finds no housekeeping CPU left for the boot domain and >>> hits WARNs and an OOPS in partition_sched_domains(). >>> housekeeping_update() cannot accept the configuration either as it >>> cannot empty the boot domain housekeeping mask. >>> With an "isolcpus=domain,10-31" boot where CPUs 0-9 are the boot >>> domain housekeeping CPUs, for example: >>> >>>    # echo 0-9 > A/cpuset.cpus >>>    # echo isolated > A/cpuset.cpus.partition >>>    WARNING: kernel/sched/topology.c:3089 at build_sched_domains+... >>>    WARNING: kernel/cgroup/cpuset.c:1478 at cpuset_update_sd_hk_unlock+... >>>    RIP: 0010:partition_sched_domains+0x3b8 >>> >>> Fix that by extending prstate_housekeeping_conflict() to reject an >>> isolated partition update that would leave no active boot domain >>> housekeeping CPU outside the isolated CPUs. The CPUs released back >>> to the boot domain by the same update are taken into account, so >>> replacing one of the last housekeeping CPUs with another one in a >>> single update remains allowed. The new check is only performed when >>> housekeeping_enabled(HK_TYPE_KERNEL_NOISE) is disabled so that the >>> existing nohz_full behavior is unchanged. >>> >>> Add test cases in test_cpuset_prs.sh to verify that taking over all >>> the boot domain housekeeping CPUs is rejected while swapping one of >>> them with another one is allowed. >> >> Hi Guopeng, >> >> Thanks for the report and the reproducer. I can reproduce the WARN and >> the OOPS in partition_sched_domains() here. >> >> However, I don't think prstate_housekeeping_conflict() is the right >> place to fix it, and the fix doesn't seem complete. The same problem >> can be triggered with a root partition, which this patch doesn't cover. >> With an "isolcpus=domain,4-7" boot on an 8-CPU VM: >> >>   # echo 0-3 > A/cpuset.cpus >>   # echo root > A/cpuset.cpus.partition >>   WARNING: kernel/sched/topology.c:3111 at build_sched_domains+0x2b96/0x5500 >>   Oops: general protection fault, ... [#1] SMP KASAN NOPTI >>   RIP: 0010:partition_sched_domains+0x10a3/0x1a10 >> >> The faulting address is in build_perf_domains(), where cpumask_first() >> on the empty cpu_map returns nr_cpu_ids and cpu_rq() goes out of >> bounds. >> >> The root cause looks like it isn't a housekeeping conflict. Boot time >> isolated CPUs stay in top_cpuset.effective_cpus by design, and they are >> only filtered out of the top_cpuset sched domain in >> generate_sched_domains(). But the checks that make sure the parent >> still has CPUs left, i.e. tasks_nocpu_error() for local partitions and >> the cpumask_subset(top_cpuset.effective_cpus, ...) checks in >> remote_partition_enable()/remote_cpus_update(), only look at >> top_cpuset.effective_cpus. So any partition, root or isolated, local >> or remote, can take away all the boot domain housekeeping CPUs as long >> as some boot isolated CPUs are still left in top_cpuset, which leaves >> the top_cpuset sched domain empty. >> >> So I think the check should be done at the "parent has no CPU left" >> level instead. Something like the diff below. It is not tested yet; >> could you give it a try with your reproducer and the test cases? >> Note that the root partition and remote partition cases should be >> added to the selftest as well. >> >> Without isolcpus=domain, HK_TYPE_DOMAIN_BOOT is cpu_possible_mask and >> the new check is equivalent to the existing one, so no extra >> housekeeping_enabled() gating is needed. >> >> --- >> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c >> index 3219f927c35e..fb3e81405f5b 100644 >> --- a/kernel/cgroup/cpuset.c >> +++ b/kernel/cgroup/cpuset.c >> @@ -1180,12 +1180,51 @@ static void update_partition_sd_lb(struct cpuset *cs, >> int old_prs) >>                 cpuset_force_rebuild(); >>  } >> >> +/* >> + * top_cpuset_sd_nocpu - Check if top_cpuset will have no sched domain CPU >> + * @add_cpus: CPUs to be taken away from top_cpuset >> + * @del_cpus: CPUs to be given back to top_cpuset, can be NULL >> + * Return: true if no active CPU will be left in the top_cpuset sched domain >> + * >> + * Boot time isolated CPUs stay in top_cpuset.effective_cpus, but they are >> + * excluded from the sched domain of top_cpuset in generate_sched_domains(). >> + * So checking top_cpuset.effective_cpus alone is not enough to ensure that >> + * the top_cpuset sched domain won't become empty after @add_cpus are taken >> + * away from it. The sched domain of top_cpuset must keep at least one >> + * active boot domain housekeeping CPU. >> + */ >> +static bool top_cpuset_sd_nocpu(const struct cpumask *add_cpus, >> +                               const struct cpumask *del_cpus) >> +{ >> +       const struct cpumask *hk_mask = >> housekeeping_cpumask(HK_TYPE_DOMAIN_BOOT); >> +       int cpu; >> + >> +       for_each_cpu_and(cpu, hk_mask, cpu_active_mask) { >> +               if (cpumask_test_cpu(cpu, add_cpus)) >> +                       continue; >> +               if (cpumask_test_cpu(cpu, top_cpuset.effective_cpus) || >> +                   (del_cpus && cpumask_test_cpu(cpu, del_cpus))) >> +                       return false; >> +       } >> +       return true; >> +} >> + >>  /* >>   * tasks_nocpu_error - Return true if tasks will have no effective_cpus >>   */ >>  static bool tasks_nocpu_error(struct cpuset *parent, struct cpuset *cs, >>                               struct cpumask *xcpus) >>  { >> +       /* >> +        * The top_cpuset always has tasks (kthreads at least), so its sched >> +        * domain can't be empty. The current effective_xcpus of a valid >> +        * partition will be given back to top_cpuset if not in @xcpus. >> +        */ >> +       if ((parent == &top_cpuset) && >> +           top_cpuset_sd_nocpu(xcpus, is_partition_valid(cs) >> +                                      ? cs->effective_xcpus : NULL)) > > The del_cpus should normally be (cs->effective_xcpus & ~xcpus), but the > top_cpuset_sd_nocpu() helper will skip CPUs that are in xcpus. So it will work > in this case. It should be noted in the functional comment of > top_cpuset_sd_nocpu() that @del_cpus can include common CPUs that will stay in > the partition which will be skipped in the helper so that future change won't > accidentally change that behavior. > Thank you for your reply. Yes, perhaps Guopeng could make the code and comments more readable. > >> + return true; >> + >>         /* >>          * A populated partition (cs or parent) can't have empty effective_cpus >>          */ >> @@ -1724,7 +1763,7 @@ static int remote_partition_enable(struct cpuset *cs, >> int new_prs, >>          */ >>         compute_excpus(cs, tmp->new_cpus); >>         if (!cpumask_intersects(tmp->new_cpus, cpu_active_mask) || >> -           cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus)) >> +           top_cpuset_sd_nocpu(tmp->new_cpus, NULL)) >>                 return PERR_INVCPUS; >>         if (cpumask_intersects(tmp->new_cpus, subpartitions_cpus)) >>                 return PERR_NOCPUS; >> @@ -1828,7 +1867,7 @@ static void remote_cpus_update(struct cpuset *cs, struct >> cpumask *xcpus, >>                 if (!capable(CAP_SYS_ADMIN)) >>                         WRITE_ONCE(cs->prs_err, PERR_ACCESS); >>                 else if (cpumask_intersects(tmp->addmask, subpartitions_cpus) || >> -                        cpumask_subset(top_cpuset.effective_cpus, tmp->addmask)) >> +                        top_cpuset_sd_nocpu(tmp->addmask, tmp->delmask)) >>                         WRITE_ONCE(cs->prs_err, PERR_NOCPUS); >>                 else if (prstate_housekeeping_conflict(prs, PRS_ROOT, >>                                                        excpus, tmp->delmask)) >> > -- Best regards Ridong