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Cc: Guopeng Zhang , Ridong Chen , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Chen Ridong , Ridong Chen Subject: [RFC PATCH -v4 13/22] cpuset: introduce local_partition_update() Date: Sun, 1 Nov 2026 19:41:57 +0800 Message-Id: <20261101114206.2434398-14-ridong.chen@linux.dev> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20261101114206.2434398-1-ridong.chen@linux.dev> References: <20261101114206.2434398-1-ridong.chen@linux.dev> X-Mailing-List: cgroups@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: Chen Ridong The local_partition_update() function replaces the command partcmd_update previously handled within update_parent_effective_cpumask(). The update logic follows a state-based approach: 1. Validation check: First verify if the local partition is currently valid 2. Invalidation handling: If the partition is invalid, trigger invalidation 3. State transition: If an invalid partition has no errors, transition to valid 4. cpumask updates: For a local partition whose cpumask only changes, use partition_update() to handle the change. validate_local_partition() is added to check the local partition specific requirements: the parent must be a valid partition root, a root partition is not allowed under an isolated parent, and optionally the user exclusive CPUs must not overlap with any sibling. It then calls validate_partition() for the common checks. local_partition_update() computes the new effective exclusive CPUs with compute_excpus() as before. As in the old partcmd_update path, the sibling exclusivity check is only done for an invalid partition with an empty cpuset.cpus.exclusive, as a valid partition has passed it already. If an invalid partition fails the validation again, only its error code is updated, unless its parent is not a valid partition root. In that case, e.g. for a remote partition invalidated by hotplug, the original error code is kept as the cpuset can't become a valid local partition anyway. In update_cpumasks_hier(), effective_cpus of the child is now updated before local_partition_update() is called, as tmp->new_cpus is reused by it. For the same reason, the effective cpumask is always recomputed afterwards. Signed-off-by: Chen Ridong Signed-off-by: Ridong Chen --- kernel/cgroup/cpuset.c | 171 +++++++++++++++++++++++++++++++++++++++-- 1 file changed, 163 insertions(+), 8 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 822cc1d97fca..d2cb989beab9 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -2074,6 +2074,155 @@ static void local_partition_disable(struct cpuset *cs, enum prs_errcode part_err update_sibling_cpumasks(parent, cs, tmp); } +static bool is_user_xcpus_exclusive(struct cpuset *cs) +{ + struct cpuset *parent = parent_cs(cs); + struct cgroup_subsys_state *css; + struct cpuset *child; + bool exclusive = true; + + rcu_read_lock(); + cpuset_for_each_child(child, css, parent) { + if (child == cs) + continue; + if (!cpusets_are_exclusive(cs, child)) { + exclusive = false; + break; + } + } + rcu_read_unlock(); + return exclusive; +} + +/** + * validate_local_partition - Validate for local partition + * @cs: Target cpuset to validate + * @new_prs: New partition root state to validate + * @excpus: New effective exclusive CPUs mask to validate + * @excl_check: Flag to enable exclusive CPUs ownership validation + * @tmp: Temporary masks + * + * Return: PERR_NONE if validation passes, appropriate error code otherwise + * + * Important: The caller must ensure that @cs's cpu mask is updated before + * invoking this function when exclusive CPU validation is required. + */ +static enum prs_errcode validate_local_partition(struct cpuset *cs, int new_prs, + struct cpumask *excpus, bool excl_check, struct tmpmasks *tmp) +{ + struct cpuset *parent = parent_cs(cs); + + /* The parent must be a partition root */ + if (!is_partition_valid(parent)) { + return is_partition_invalid(parent) + ? PERR_INVPARENT : PERR_NOTPART; + } + + /* A root partition is not allowed under an isolated parent */ + if (new_prs == PRS_ROOT && parent->partition_root_state == PRS_ISOLATED) + return PERR_ISOPARENT; + + if (excl_check && !is_user_xcpus_exclusive(cs)) + return PERR_NOTEXCL; + + return validate_partition(cs, parent, new_prs, excpus, + tmp ? tmp->delmask : NULL); +} + +/** + * __local_partition_update - Update local partition configuration + * @cs: Target cpuset to update + * @xcpus: New exclusive CPU mask + * @excpus: New effective exclusive CPU mask + * @tmp: Temporary mask storage for intermediate calculations + * @excl_check: Flag to enable exclusivity validation + * + * Handles updates to local CPU partition configurations by validating + * changes, managing state transitions, and propagating updates through + * the cpuset hierarchy. + * + * Note on exclusivity checking: Exclusivity validation is required when + * transitioning from an invalid to valid partition state. However, when + * updating cpus_allowed or exclusive_cpus, exclusivity should have already + * been verified by validate_change(). In such cases, excl_check must be + * false since the cs cpumasks are not yet updated. + * + * Return: Partition error code (PERR_NONE indicates success) + */ +static int __local_partition_update(struct cpuset *cs, struct cpumask *xcpus, + struct cpumask *excpus, struct tmpmasks *tmp, + bool excl_check) +{ + struct cpuset *parent = parent_cs(cs); + int part_error = PERR_NONE; /* Partition error? */ + int old_prs, new_prs; + + lockdep_assert_cpuset_lock_held(); + /* For local partition only */ + if (WARN_ON_ONCE(is_remote_partition(cs) || cs_is_member(cs))) + return PERR_NONE; + + old_prs = cs->partition_root_state; + /* + * If new_prs < 0, it might transition to valid partition state. + * Use absolute value for validation checks. + */ + new_prs = old_prs < 0 ? -old_prs : old_prs; + cpumask_andnot(tmp->addmask, excpus, cs->effective_xcpus); + cpumask_andnot(tmp->delmask, cs->effective_xcpus, excpus); + part_error = validate_local_partition(cs, new_prs, excpus, + excl_check, tmp); + if (part_error) { + /* + * An invalid partition only needs to update its error code. + * Keep the error code if the parent is not a valid partition + * root, e.g. for an invalidated remote partition, as the + * cpuset can't become a valid local partition anyway. + */ + if (is_partition_valid(cs)) + local_partition_disable(cs, part_error, tmp); + else if (is_partition_valid(parent)) + WRITE_ONCE(cs->prs_err, part_error); + return part_error; + } + + /* Nothing changes, return PERR_NONE */ + if (new_prs == old_prs && + (cpumask_empty(tmp->addmask) && cpumask_empty(tmp->delmask))) + return PERR_NONE; + + /* + * If partition was previously invalid but now passes checks, + * re-enable it and update related flags. + * Otherwise, partition state doesn't change, only cpumasks change. + */ + if (is_partition_invalid(cs)) { + partition_enable(cs, parent, new_prs, excpus); + update_partition_sd_lb(cs, old_prs); + } else { + partition_update(cs, new_prs, xcpus, excpus, tmp); + } + + cpuset_update_tasks_cpumask(parent, tmp->addmask); + update_sibling_cpumasks(parent, cs, tmp); + return PERR_NONE; +} + +static int local_partition_update(struct cpuset *cs, struct tmpmasks *tmp) +{ + /* + * A valid partition has passed the exclusivity check already. An + * invalid partition has to pass it before becoming valid again when + * cpuset.cpus.exclusive is empty. + */ + bool excl_check = is_partition_invalid(cs) && + cpumask_empty(cs->exclusive_cpus); + + compute_excpus(cs, tmp->new_cpus); + return __local_partition_update(cs, NULL, tmp->new_cpus, tmp, + excl_check); +} + /** * update_parent_effective_cpumask - update effective_cpus mask of parent cpuset * @cs: The cpuset that requests change in partition root state @@ -2483,17 +2632,23 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp, if (!css_tryget_online(&cp->css)) continue; rcu_read_unlock(); + /* + * The tmp->new_cpus may be modified. + * Update effective_cpus before passing tmp to other functions. + */ + spin_lock_irq(&callback_lock); + cpumask_copy(cp->effective_cpus, tmp->new_cpus); + spin_unlock_irq(&callback_lock); if (update_parent) { - update_parent_effective_cpumask(cp, partcmd_update, NULL, tmp); + local_partition_update(cp, tmp); /* * Capture current partition_root_state as it may have - * changed. Recompute effective cpumask if changed. + * changed. tmp->new_cpus is reused by + * local_partition_update(), recompute effective cpumask. */ new_prs = cp->partition_root_state; - if (new_prs != old_prs) { - compute_effective_cpumask(tmp->new_cpus, cp, parent); - } + compute_effective_cpumask(tmp->new_cpus, cp, parent); } spin_lock_irq(&callback_lock); @@ -2650,8 +2805,8 @@ static void partition_cpus_change(struct cpuset *cs, struct cpuset *trialcs, if (trialcs->prs_err) local_partition_disable(cs, trialcs->prs_err, tmp); else - update_parent_effective_cpumask(cs, partcmd_update, - trialcs->effective_xcpus, tmp); + __local_partition_update(cs, trialcs->exclusive_cpus, + trialcs->effective_xcpus, tmp, false); } } @@ -4138,7 +4293,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp) else if (is_partition_valid(parent) && is_partition_invalid(cs) && !cpumask_empty(user_xcpus(cs))) { partcmd = partcmd_update; - update_parent_effective_cpumask(cs, partcmd, NULL, tmp); + local_partition_update(cs, tmp); } if (partcmd >= 0) { -- 2.34.1