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Thu, 12 Nov 2026 19:15:47 +0000 (UTC) Received: from [100.91.18.181] (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 7E590410; Thu, 12 Nov 2026 19:15:45 +0000 (UTC) Message-ID: <5402d139-37bf-408a-b956-6c76b8832710@redhat.com> Date: Thu, 12 Nov 2026 14:15:44 -0500 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 for-7.4-fixes v4 2/2] cpuset: generalize the validate_partition() interface To: Ridong Chen , Tejun Heo , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Shuah Khan Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Guopeng Zhang , Ridong Chen References: <20261112031931.2815548-1-ridong.chen@linux.dev> <20261112031931.2815548-3-ridong.chen@linux.dev> Content-Language: en-US From: Waiman Long In-Reply-To: <20261112031931.2815548-3-ridong.chen@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.6 on 10.30.177.95 On 11/11/26 10:19 PM, Ridong Chen wrote: > From: Ridong Chen > > Refactor validate_partition() to take the parent partition, the new > partition root state, the new effective exclusive CPUs and the CPUs to > be deleted, instead of a trial cpuset. A NULL parent stands for a > remote partition, whose CPUs come from top_cpuset. This makes the > interface flexible enough to handle both local and remote partition > validation. > > This also fixes a false PERR_NOCPUS error when expanding a remote > partition. The no CPU left for tasks check in partition_cpus_change() > is done against the cgroup parent, but the CPUs of a remote partition > come from top_cpuset, not from its parent. For example, on a 4-CPU > system: > > echo 2-3 > P/cpuset.cpus > echo 2-3 > P/cpuset.cpus.exclusive > echo 2-3 > P/C/cpuset.cpus > echo 2 > P/C/cpuset.cpus.exclusive > echo root > P/C/cpuset.cpus.partition > (a task in P) > echo 2-3 > P/C/cpuset.cpus.exclusive > cat P/C/cpuset.cpus.partition > root invalid (Parent is not a partition root) > > The effective_cpus of P is 3, a subset of the new exclusive CPUs 2-3 of > C, and P has a task, so the expansion is rejected. However, P is not a > partition root and does not give any CPU to C, and top_cpuset still has > CPUs 0-1 for the task. Enabling C directly with exclusive CPUs 2-3 > succeeds, as remote_partition_enable() checks top_cpuset instead. > > The no CPU left for tasks check now uses the given parent instead of > parent_cs(cs), and top_cpuset for a remote partition, as that is where > its CPUs are taken from. > > The housekeeping conflict check is folded into validate_partition(). It > is skipped when the parent is not a valid partition root, as @cs can't > be a valid local partition in that case. > > Use the new interface for local partition enablement in > update_parent_effective_cpumask() and in partition_cpus_change(), > replacing the open-coded checks there. The order of the checks is now > the same for both paths: empty CPUs, housekeeping conflict, then no CPU > left for tasks. > > Add a test case to test_cpuset_prs.sh for the remote partition > expansion above. > > Fixes: 181c8e091aae ("cgroup/cpuset: Introduce remote partition") > Signed-off-by: Ridong Chen > --- > kernel/cgroup/cpuset.c | 119 +++++++++--------- > .../selftests/cgroup/test_cpuset_prs.sh | 5 + > 2 files changed, 64 insertions(+), 60 deletions(-) > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index c7d4cfb615b7..7e374210c123 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -1414,6 +1414,48 @@ static bool prstate_housekeeping_conflict(int new_prs, int parent_prs, > return res; > } > > +/** > + * validate_partition - Validate a cpuset partition configuration > + * @cs: The cpuset to validate > + * @parent: Parent partition of @cs, NULL for remote partition > + * @new_prs: The proposed new partition root state > + * @new_excpus: The new effective exclusive CPUs mask to validate > + * @del: exclusive CPUs to be deleted from @cs, can be NULL > + * > + * A remote partition gets its CPUs from top_cpuset, so top_cpuset is used > + * as the parent when @parent is NULL. > + * > + * The housekeeping check is skipped if @parent is not a valid partition > + * root as @cs can't be a valid local partition in that case. > + * > + * Return: PRS error code (0 if valid, non-zero error code if invalid) > + */ > +static enum prs_errcode validate_partition(struct cpuset *cs, > + struct cpuset *parent, int new_prs, > + struct cpumask *new_excpus, > + struct cpumask *del) > +{ > + int parent_prs; > + > + if (new_prs == PRS_MEMBER) > + return PERR_NONE; > + > + if (cpumask_empty(new_excpus)) > + return PERR_INVCPUS; > + > + if (!parent) > + parent = &top_cpuset; > + parent_prs = parent->partition_root_state; > + if (parent_prs > 0 && > + prstate_housekeeping_conflict(new_prs, parent_prs, new_excpus, del)) > + return PERR_HKEEPING; > + > + if (tasks_nocpu_error(parent, cs, new_excpus)) > + return PERR_NOCPUS; > + > + return PERR_NONE; > +} > + > /* > * cpuset_update_sd_hk_unlock - Rebuild sched domains, update HK & unlock > * > @@ -1934,18 +1976,10 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, > if ((cmd == partcmd_enable) || (cmd == partcmd_enablei)) { > new_prs = (cmd == partcmd_enable) ? PRS_ROOT : PRS_ISOLATED; > > - /* > - * Enabling partition root is not allowed if its > - * effective_xcpus is empty. > - */ > - if (cpumask_empty(tmp->delmask)) > - return PERR_INVCPUS; > - > - if (prstate_housekeeping_conflict(new_prs, parent_prs, tmp->delmask, NULL)) > - return PERR_HKEEPING; > - > - if (nocpu) > - return PERR_NOCPUS; > + part_error = validate_partition(cs, parent, new_prs, > + tmp->delmask, NULL); > + if (part_error) > + return part_error; > > /* > * This function will only be called when all the preliminary > @@ -2428,32 +2462,6 @@ static int parse_cpuset_cpulist(const char *buf, struct cpumask *out_mask) > return 0; > } > > -/** > - * validate_partition - Validate a cpuset partition configuration > - * @cs: The cpuset to validate > - * @trialcs: The trial cpuset containing proposed configuration changes > - * > - * If any validation check fails, the appropriate error code is set in the > - * cpuset's prs_err field. > - * > - * Return: PRS error code (0 if valid, non-zero error code if invalid) > - */ > -static enum prs_errcode validate_partition(struct cpuset *cs, struct cpuset *trialcs) > -{ > - struct cpuset *parent = parent_cs(cs); > - > - if (cs_is_member(trialcs)) > - return PERR_NONE; > - > - if (cpumask_empty(trialcs->effective_xcpus)) > - return PERR_INVCPUS; > - > - if (tasks_nocpu_error(parent, cs, trialcs->effective_xcpus)) > - return PERR_NOCPUS; > - > - return PERR_NONE; > -} > - > /** > * partition_cpus_change - Handle partition state changes due to CPU mask updates > * @cs: The target cpuset being modified > @@ -2467,33 +2475,24 @@ static void partition_cpus_change(struct cpuset *cs, struct cpuset *trialcs, > struct tmpmasks *tmp) > { > enum prs_errcode prs_err; > - int parent_prs = is_remote_partition(cs) > - ? PRS_ROOT : parent_cs(cs)->partition_root_state; > + struct cpuset *parent = is_remote_partition(cs) ? NULL : parent_cs(cs); > > if (cs_is_member(cs)) > return; > > - prs_err = validate_partition(cs, trialcs); > - if (!prs_err && (parent_prs > 0) && > - !cpumask_empty(trialcs->effective_xcpus)) { > - int prs = cs->partition_root_state; > - > - /* > - * Check for housekeeping conflict by passing the whole > - * effective_xcpus as well as those CPUs that are to be > - * removed from cs as delmask. > - */ > - if (prs > 0) > - cpumask_andnot(tmp->delmask, cs->effective_xcpus, > - trialcs->effective_xcpus); > - else > - cpumask_clear(tmp->delmask); > - > - if (prstate_housekeeping_conflict(prs, parent_prs, > - trialcs->effective_xcpus, tmp->delmask)) > - prs_err = PERR_HKEEPING; > - } > + /* > + * Check for housekeeping conflict by passing the whole > + * effective_xcpus as well as those CPUs that are to be > + * removed from cs as delmask. > + */ > + if (is_partition_valid(cs)) > + cpumask_andnot(tmp->delmask, cs->effective_xcpus, > + trialcs->effective_xcpus); > + else > + cpumask_clear(tmp->delmask); > > + prs_err = validate_partition(cs, parent, trialcs->partition_root_state, > + trialcs->effective_xcpus, tmp->delmask); > if (prs_err) { > WRITE_ONCE(cs->prs_err, prs_err); > trialcs->prs_err = prs_err; > diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh > index 1e9e6b4c6f7b..1397ec428c46 100755 > --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh > +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh > @@ -707,6 +707,11 @@ REMOTE_TEST_MATRIX=( > " C1-4:P1 C5-6 C1-2 . C5 . \ > . P1 P1 . O5=0 . p1:3-4|p2:6|c11:1-2|c12:3-4|c21:6|c22:6 \ > p1:P1|p2:P1|c11:P1" > + # Expanding a remote partition should check top cpuset, not its member > + # parent, for the no CPU left for tasks error. > + " CX2-3:T . C2-3:X2:P1 . . . \ > + . . X2-3 . . . p1:1,4-7|c11:2-3 \ > + p1:P0|c11:P1" > ) > > # LGTM Reviewed-by: Waiman Long