From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.137 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794404602; b=BrFafpjKuD7UbfnH46KLmWaJ+/jvr8AX8jL9ZCE2XPOffxpWMaSYQGV+mumXH5NThUrH Y+nHZLlWCUEtBFTrNioTMAtLx5vTrL4hdtlnGaumLIHobs0OpIztsM+bczM3gNEJ7+DCB vhD2eKuu70AJjz03XZQm+FCIe/B55caq2QNk7qyTX4DDgIiIE/iAgeuLC4YCXgnEogYFD 8Fe3/Gp3IjeM16huq+DEv2uLUQJ5IwUXrbymAaB2OEkiFlx0fdBUgIy+txjB4VumYYRDg 5aaZ2k6L+1Zgu4gOE3kgOdgJwQ8I6Hdx5OSWy+PWrgP9rLEH5MUJJT0d6f7YGIIi/sA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794404602; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:From:To:Cc:Subject:Date:Message-ID: X-Mailer:In-Reply-To:References:MIME-Version: Content-Transfer-Encoding; bh=TrL5aZEGY7ELvwzZmsr3OzogHrnn0YtKNmLfnroTfdQ=; b=4a9NYaxCuBaUVDqbiQO508NXhr6g0aNIHc3+o7jubgVyYwpKt8oTkk1TVxNaNmw2fLoa XpiSEhBNJT7AWP+UrTGFlSiVSvSAHSMgHZW0qnrLP3xavMlk3u7yPupV/f4fN9LCRv9GF 8GEu1ZLIrX1RxAt9jFYDIDslA6D5SBeyXB49gkq+k9MMIuliGjdQkss4D2uLVAMvjFoHq bv9jLu4mo9vFunGXCcYlNjgtPXS4C83UsvhWkVGawZGLOfNdMj5uiMKbkTzFJFduHpgqK iDJQuLTuvXOWK4btHWEK+ArlmwzQ8ZZ4nvR+tk+783SCYBE56+XOwZ0ouaZN8zrY5FQ== 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=l2YbfwzL; arc=none smtp.remote-ip=91.218.175.137 Received: from mta0.migadu.com (out-137.mta0.migadu.com [91.218.175.137]) (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 C7590606A8B3 for ; Wed, 11 Nov 2026 13:43:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org C7590606A8B3 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=l2YbfwzL X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=S5OwXDkOwkAkwbhRydD64b+NkJ3J9OBg/ir+UTXErTU=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1794404599; v=1; x=1795009399; b=l2YbfwzLL4Xh5o4VKBSWSkdf+IW+gXvmLjKGe7qwW51PFQHS82nf137/FfKta60o5yh87kKz bh+sRhc4lfG1AT5uvlb2j2u7X2IMnlru+IMnASsDgdB7VBsmgWrpQ8J+ijvKfBhIQpFWqapp9mC Ira7iV+AYhkgI6fs22niPDyI= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id ad63f5dbd3771748; Wed, 11 Nov 2026 13:43:19 +0000 X-Mizu-Trace-ID: ad63f5dbd3771748 X-Migadu-Flow: FLOW_OUT From: Guopeng Zhang To: longman@redhat.com, ridong.chen@linux.dev Cc: cgroups@vger.kernel.org, tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com, shuah@kernel.org, mathieu.desnoyers@efficios.com, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Guopeng Zhang , Ridong Chen Subject: [PATCH v4 1/2] cgroup/cpuset: Keep an active housekeeping CPU in the top sched domain Date: Wed, 11 Nov 2026 21:42:49 +0800 Message-ID: <20261111134250.16852-2-guopeng.zhang@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261111134250.16852-1-guopeng.zhang@linux.dev> References: <20261111134250.16852-1-guopeng.zhang@linux.dev> 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 Content-Transfer-Encoding: 8bit From: Guopeng Zhang Boot-isolated CPUs remain in top_cpuset.effective_cpus, but are excluded from its scheduling domain. A partition can therefore take all boot domain housekeeping CPUs while leaving effective_cpus nonempty. For example, on a 32-CPU system with all CPUs online and isolcpus=domain,10-31: echo 0-9 > A/cpuset.cpus echo root > A/cpuset.cpus.partition Oops: general protection fault RIP: 0010:build_perf_domains+... tasks_nocpu_error() also rejects valid CPU replacements because it does not account for CPUs returned by the update. With a fresh cgroup A under the same boot configuration: echo 2-31 > 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 5-31 to top_cpuset, including housekeeping CPUs 5-9, and leave A valid. This replacement failure also occurs without boot isolation and under populated local parents. Extend tasks_nocpu_error() to take an explicit mask of CPUs being returned and use it for local and remote updates. Require an active HK_TYPE_DOMAIN_BOOT CPU to remain in top_cpuset. For other populated parents, check within their current exclusive grant so an ancestor update cannot credit CPUs that the parent no longer owns. CPU hotplug can also empty the top scheduling domain. Pass no returned CPUs during its availability check, and only invalidate a partition to restore the top domain if it can return an active boot domain housekeeping CPU. Still invalidate a populated partition that has no active CPU of its own. Fixes: 9b496a8bbed9 ("cgroup/cpuset: Prevent leakage of isolated CPUs into sched domains") Fixes: 0c7f293efc87 ("cgroup/cpuset: Add cpuset.cpus.exclusive.effective for v2") Co-developed-by: Ridong Chen Signed-off-by: Ridong Chen Signed-off-by: Guopeng Zhang --- kernel/cgroup/cpuset.c | 85 ++++++++++++++++++++++++++++++++++-------- 1 file changed, 70 insertions(+), 15 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 3052413e41e7..85f92ae0c6f4 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1181,18 +1181,54 @@ static void update_partition_sd_lb(struct cpuset *cs, int old_prs) } /* - * tasks_nocpu_error - Return true if tasks will have no effective_cpus + * tasks_nocpu_error - Return true if tasks or the top domain lack active CPUs + * @parent: parent partition, NULL for a remote partition + * @cs: the partition + * @xcpus: exclusive CPUs that @cs will hold after the update + * @del_cpus: exclusive CPUs to be returned to @parent, can be NULL + * + * @del_cpus may include CPUs that are also in @xcpus and will stay in + * @cs. They are skipped by the @xcpus check, so callers can pass the + * current effective_xcpus of @cs without masking it first. + * + * top_cpuset always has tasks. Boot-isolated CPUs remain in its + * effective_cpus but are excluded from its sched domain, which must + * retain an active boot domain housekeeping CPU. */ static bool tasks_nocpu_error(struct cpuset *parent, struct cpuset *cs, - struct cpumask *xcpus) + const struct cpumask *xcpus, + const struct cpumask *del_cpus) { + const struct cpumask *mask; + int cpu; + + /* A populated @cs must have an active CPU in @xcpus. */ + if (!cpumask_intersects(xcpus, cpu_active_mask) && + partition_is_populated(cs, NULL)) + return true; + /* - * A populated partition (cs or parent) can't have empty effective_cpus + * A populated @parent must keep an active CPU in @mask, either from + * its effective_cpus or from @del_cpus, that isn't taken by @cs. */ - return (cpumask_subset(parent->effective_cpus, xcpus) && - partition_is_populated(parent, cs)) || - (!cpumask_intersects(xcpus, cpu_active_mask) && - partition_is_populated(cs, NULL)); + if (!parent) + parent = &top_cpuset; + + /* CPUs outside the parent's current grant cannot be returned. */ + mask = parent->effective_xcpus; + if (parent == &top_cpuset) + mask = housekeeping_cpumask(HK_TYPE_DOMAIN_BOOT); + else if (!partition_is_populated(parent, cs)) + return false; + + for_each_cpu_and(cpu, mask, cpu_active_mask) { + if (cpumask_test_cpu(cpu, xcpus)) + continue; + if (cpumask_test_cpu(cpu, parent->effective_cpus) || + (del_cpus && cpumask_test_cpu(cpu, del_cpus))) + return false; + } + return true; } static void reset_partition_data(struct cpuset *cs) @@ -1724,7 +1760,7 @@ 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)) + tasks_nocpu_error(NULL, cs, tmp->new_cpus, NULL)) return PERR_INVCPUS; if (cpumask_intersects(tmp->new_cpus, subpartitions_cpus)) return PERR_NOCPUS; @@ -1828,7 +1864,7 @@ 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)) + tasks_nocpu_error(NULL, cs, excpus, cs->effective_xcpus)) WRITE_ONCE(cs->prs_err, PERR_NOCPUS); else if (prstate_housekeeping_conflict(prs, PRS_ROOT, excpus, tmp->delmask)) @@ -1961,7 +1997,8 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, */ if ((cmd != partcmd_disable) && !newmask) { compute_excpus(cs, tmp->delmask); - nocpu = tasks_nocpu_error(parent, cs, tmp->delmask); + nocpu = tasks_nocpu_error(parent, cs, tmp->delmask, + is_partition_valid(cs) ? cs->effective_xcpus : NULL); } if ((cmd == partcmd_enable) || (cmd == partcmd_enablei)) { @@ -2497,7 +2534,9 @@ static enum prs_errcode validate_partition(struct cpuset *cs, struct cpuset *tri if (cpumask_empty(trialcs->effective_xcpus)) return PERR_INVCPUS; - if (tasks_nocpu_error(parent, cs, trialcs->effective_xcpus)) + if (tasks_nocpu_error(is_remote_partition(cs) ? NULL : parent, cs, + trialcs->effective_xcpus, + is_partition_valid(cs) ? cs->effective_xcpus : NULL)) return PERR_NOCPUS; return PERR_NONE; @@ -3997,6 +4036,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp) static nodemask_t new_mems; bool cpus_updated; bool mems_updated; + bool nocpu; int partcmd = -1; struct cpuset *parent; @@ -4008,9 +4048,23 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp) if (!tmp || !cs->partition_root_state) goto update_tasks; - if (is_remote_partition(cs) && (cpumask_empty(subpartitions_cpus) || - (cpumask_empty(&new_cpus) && - partition_is_populated(cs, NULL)))) { + /* Do not count any CPUs as returned during this hotplug check. */ + nocpu = tasks_nocpu_error(is_remote_partition(cs) ? NULL : parent, cs, + &new_cpus, NULL); + if (nocpu && (parent == &top_cpuset || is_remote_partition(cs))) { + /* + * Only invalidate a partition for an empty top sched domain if + * it can return an active boot domain housekeeping CPU. A + * populated partition with no active CPU must still be invalidated. + */ + cpumask_and(tmp->addmask, cs->effective_xcpus, + housekeeping_cpumask(HK_TYPE_DOMAIN_BOOT)); + if (!cpumask_intersects(tmp->addmask, cpu_active_mask)) + nocpu = cpumask_empty(&new_cpus) && + partition_is_populated(cs, NULL); + } + + if (is_remote_partition(cs) && (cpumask_empty(subpartitions_cpus) || nocpu)) { WRITE_ONCE(cs->prs_err, PERR_HOTPLUG); remote_partition_disable(cs, tmp); compute_effective_cpumask(&new_cpus, cs, parent); @@ -4023,10 +4077,11 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp) * 2) parent is invalid or doesn't grant any cpus to child * partitions. * 3) subpartitions_cpus is empty. + * 4) top_cpuset needs an active boot domain housekeeping CPU from cs. */ if (is_local_partition(cs) && (!is_partition_valid(parent) || - tasks_nocpu_error(parent, cs, &new_cpus) || + nocpu || cpumask_empty(subpartitions_cpus))) partcmd = partcmd_invalidate; /* -- 2.43.0