From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.198 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793797096; b=z4sRxWpD3bUHE/fZVCK0K4gHyDdrZy8BA3b8YIqz7uQyCPb0D+9BDhvjmWJXMrsM/uRr 8cQKE8aAFKnUbEBFxotQYIPYiFP4BsgTioYOn6140EKJ9dolzUdNQFv5hKNDLu3nh7Ctb kJPqE8usVYci/NRVU9m0ecIwBf0z2J8rPhRztfshKOw+THcR9n+e7FMYtvfAe1n8QZpe+ kiYeJKF5byU0tmLClwhFTbuODlLpUVVHa678y5rdCBEXH2kR1dJZw3sVLtDDi3ms8KuSB uyg56F3CM32Je0/ARyMDqqmunC8y5XkMGE01vN6o4vfdAThCmnnTaonTHrfiY5NeOfA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793797096; 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=6jRl+MNBW9eJzK1310m+ol+TnpF7kkR6PE11DxtOf5w=; b=IiiZZ2khQUyO/K1foRZyKRaU5Hgi7FF4VuqRfY97H9LrK0w6b3BeuUAGakWxrrUZ6hnt u2GH7iNY+bNBBwsMRbaohrOU8OyDHbwn0S3WHyF5sKWRHRLfsioY8NTsXgKqhz+SbgahE kG6io9I7ORxDew+OTdh0RErYkypO7nqJZAx4vsHDl+q1nTh0i2ZaLFSzcGt4BWgfqSbHm 1O8O2jZl7PWjsDN9SBFtICm3V3ZnEGMTLjvTyp4ZdsbNQD1DD8wAWY1hLBIw4+wBTBRxy oykrYxuLsDYLRB0qTytw+P2LF7gFHict5HURxPghSFxhB2lVOdSPNcXywTeDvfeprxQ== 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=xUYeFftH; arc=none smtp.remote-ip=91.218.175.198 Received: from mta0.migadu.com (out-198.mta0.migadu.com [91.218.175.198]) (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 AE87D606A32C for ; Wed, 4 Nov 2026 12:58:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org AE87D606A32C 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=xUYeFftH X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=eCNtIyjBZay778XSnVoMLQk3OiuNry21KUjRM5jXB7w=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793797091; v=1; x=1794401891; b=xUYeFftHY5ndOET3D+bn4yBe9SamfnGsOn8GGxfCQpIfEP/Ljms2w/NCmeR6w2sC2jzJjF/w 8JLPAo0QCT2PU9GGbGUFJQJYCIlhXUbaESH2Oxn7Bup8ECrO6g2p91rPuKqYM8XjMvZhbK42Ix0 ykF8qZMHnA4oDen8aipbK3CA= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 8479a0f7763f9f6b; Wed, 04 Nov 2026 12:58:10 +0000 X-Mizu-Trace-ID: 8479a0f7763f9f6b X-Migadu-Flow: FLOW_OUT Message-ID: Date: Wed, 4 Nov 2026 20:58:00 +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: Guopeng Zhang , longman@redhat.com 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> From: Ridong Chen In-Reply-To: <20261104071600.474587-1-guopeng.zhang@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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)) + 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