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Cc: Guopeng Zhang , Ridong Chen , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Ridong Chen Subject: [RFC PATCH -v4 02/22] cpuset: settle isolation state when CPUs are given back to parent Date: Sun, 1 Nov 2026 19:41:46 +0800 Message-Id: <20261101114206.2434398-3-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: Ridong Chen partition_xcpus_del() only updates isolated_cpus when the partition that gives back the CPUs has a different state than its parent. CPUs that were further distributed to descendant isolated partitions are not taken into account, so isolated_cpus_release() has to be called afterwards in several places to walk up the ancestors and fix isolated_cpus. Make partition_xcpus_del() always set the isolation state of the given back CPUs to the state of the parent that receives them. As the effective_xcpus of a partition covers the CPUs distributed to its descendants, the isolation state of those CPUs is settled at the same time. Boot-time isolated CPUs are still preserved by isolated_cpu_update(). compute_partition_effective_cpumask() invalidates a child partition without going through partition_xcpus_del(), so do the same there: the CPUs of the invalidated child take the isolation state of its parent. isolated_cpus_release() is no longer needed and is removed. Signed-off-by: Ridong Chen --- kernel/cgroup/cpuset.c | 86 ++++++++++++------------------------------ 1 file changed, 24 insertions(+), 62 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 72e1df1295e1..df9fc126e391 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1264,42 +1264,21 @@ static void isolated_cpus_update(int old_prs, int new_prs, struct cpumask *xcpus } /* - * isolated_cpus_release - Remove the relevant CPUs in @xcpus from isolated_cpus - * @cs: the current cpuset - * @xcpus: the set of effective xcpus to be considered for removal - * - * This function is called when an isolated partition is invalidated or when - * some of its effective xcpus are to be removed from isolated_cpus due to - * changes in parent cpuset. The given @xcpus must be modifiable as the function - * will update its value to determine the right set of CPUs to be removed. + * isolated_cpus_set_state - Set the isolation state of @xcpus + * @prs: partition root state that @xcpus will belong to + * @xcpus: exclusive CPUs whose isolation state may change */ -static void isolated_cpus_release(struct cpuset *cs, struct cpumask *xcpus) +static void isolated_cpus_set_state(int prs, struct cpumask *xcpus) { - struct cpuset *ancestor = parent_cs(cs); - struct cpuset *iancestor = NULL; - - /* - * Search the furthest isolated partition root ancestor available - * until top_cpuset or a remote partition root is hit. - */ - for (; ancestor; ancestor = parent_cs(ancestor)) { - if (ancestor->partition_root_state == PRS_ISOLATED) - iancestor = ancestor; - if (is_remote_partition(ancestor)) - break; - } - - /* - * If a furthest isolated partition acnestor is found, use it to - * determine which of the CPUs in @xcpus should be removed from - * isolated_cpus. Otherwise, all of them will be removed. - */ - if (iancestor && !cpumask_andnot(xcpus, xcpus, iancestor->effective_xcpus)) - return; /* No CPU should be removed from isolated_cpus */ + bool updated = false; + int cpu; - spin_lock_irq(&callback_lock); - isolated_cpus_update(PRS_ISOLATED, PRS_ROOT, xcpus); - spin_unlock_irq(&callback_lock); + lockdep_assert_held(&callback_lock); + lockdep_assert_held(&cpuset_mutex); + for_each_cpu(cpu, xcpus) + updated |= isolated_cpu_update(prs, cpu); + if (updated) + update_housekeeping = true; } /* @@ -1355,9 +1334,12 @@ static void partition_xcpus_del(int old_prs, struct cpuset *parent, if (parent == &top_cpuset) cpumask_andnot(subpartitions_cpus, subpartitions_cpus, xcpus); - if (old_prs != parent->partition_root_state) - isolated_cpus_update(old_prs, parent->partition_root_state, - xcpus); + /* + * CPUs given back to parent take the parent's isolation state. This + * also covers CPUs that were further distributed to descendant + * isolated partitions. + */ + isolated_cpus_set_state(parent->partition_root_state, xcpus); cpumask_or(parent->effective_cpus, parent->effective_cpus, xcpus); cpumask_and(parent->effective_cpus, parent->effective_cpus, cpu_active_mask); @@ -1640,14 +1622,13 @@ static void compute_partition_effective_cpumask(struct cpuset *cs, int parent_prs = cs->partition_root_state; /* - * Invalidate child partition and update isolated_cpus - * if necessary. + * Invalidate child partition. Its CPUs, including those + * further distributed to its descendants, take the + * isolation state of cs. */ spin_lock_irq(&callback_lock); WRITE_ONCE(child->prs_err, PERR_NOCPUS); - if ((old_prs == PRS_ISOLATED) && (parent_prs == PRS_ROOT)) - isolated_cpus_update(PRS_ISOLATED, PRS_ROOT, - child->effective_xcpus); + isolated_cpus_set_state(parent_prs, child->effective_xcpus); child->partition_root_state = -old_prs; spin_unlock_irq(&callback_lock); notify_partition_change(child, old_prs); @@ -2090,21 +2071,8 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, * * A partition error happens when parent has tasks and all * its effective CPUs will have to be distributed out. - * - * For an isolated partition with a shrunk root partition parent - * we may need to return some or all of its isolated CPUs. */ nocpu |= cpumask_empty(tmp->delmask); - if ((parent_prs == PRS_ROOT) && (old_prs == PRS_ISOLATED)) { - cpumask_clear(tmp->addmask); - if (nocpu) - cpumask_copy(tmp->addmask, cs->effective_xcpus); - else if (!cpumask_subset(cs->effective_xcpus, parent->effective_xcpus)) - cpumask_andnot(tmp->addmask, cs->effective_xcpus, - parent->effective_xcpus); - if (!cpumask_empty(tmp->addmask)) - isolated_cpus_release(cs, tmp->addmask); - } if (nocpu) { part_error = PERR_NOCPUS; if (is_partition_valid(cs)) @@ -2327,18 +2295,12 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp, /* * When parent is not a valid partition root, * child partition roots become invalid too. - * - * For a to be invalidated isolated partition, - * call return_isolated_cpus() to remove the - * relevant CPUs from isolated_cpus. + * The isolation state of their CPUs has been + * settled when the parent gave them back. */ if (is_partition_valid(cp)) new_prs = -old_prs; - if (old_prs == PRS_ISOLATED) { - cpumask_copy(tmp->delmask, cp->effective_xcpus); - isolated_cpus_release(cp, tmp->delmask); - } WRITE_ONCE(cp->prs_err, is_partition_invalid(parent) ? PERR_INVPARENT : PERR_NOTPART); -- 2.34.1