From 69a75e4f377629928bd173747b864694c2af4e1c Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Sun, 25 Oct 2026 17:44:40 -0400 Subject: [PATCH] cgroup/cpuset: Properly compute effective xcpus in update_parent_effective_cpumask() Since the introduction of cpuset.cpus.exclusive in commit e2ffe502ba45 ("cgroup/cpuset: Add cpuset.cpus.exclusive for v2"), a compute_effective_exclusive_cpumask() helper which is later renamed to compute_excpus() is added to compute the effective xcpus of a partition root. However update_parent_effective_cpumask() is not updated in all proper places to use the new helper to check if a given cpuset should remain a valid partition root. This can cause a cpuset to incorrectly remain a valid partition root even if no effective xcpus is left. Fix that problem by using compute_excpus() to compute the effective xcpus into delmask in all cases except partcmd_disable, partcmd_invalidate or partcmd_update with newmask set and use it for tasks_nocpu_error() check as well as checking its emptiness. This enables us to catch invalid partition root more accurately in update_parent_effective_cpumask(). In the case of partcmd_update with newmask set, the passed in new effective xcpus value will directly be used in the tasks_nocpu_error() check without relying on old data in the cpuset. For the partcmd_update with NULL newmask case, the cpu exclusivity test there is also relaxed to be performed only if exclusive_cpus is empty. Some test case are added to test_cpuset_prs.sh for invalidating a partition root due to its effective xcpus becoming empty as well as making sure that an invalid partition can only be revived when exclusive CPUs are available agin. Fixes: e2ffe502ba45 ("cgroup/cpuset: Add cpuset.cpus.exclusive for v2") Signed-off-by: Waiman Long Reviewed-by: Guopeng Zhang Tested-by: Guopeng Zhang Signed-off-by: Tejun Heo --- kernel/cgroup/cpuset.c | 87 ++++++++++--------- .../selftests/cgroup/test_cpuset_prs.sh | 11 +++ 2 files changed, 56 insertions(+), 42 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index d3ffe68324a0..34ddd434360e 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1795,7 +1795,7 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus, * update_parent_effective_cpumask - update effective_cpus mask of parent cpuset * @cs: The cpuset that requests change in partition root state * @cmd: Partition root state change command - * @newmask: Optional new cpumask for partcmd_update + * @newmask: Optional new effective xcpus for partcmd_update * @tmp: Temporary addmask and delmask * Return: 0 or a partition root state error code * @@ -1810,11 +1810,11 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus, * given back to parent's effective_cpus. 0 will always be returned. * * For partcmd_update, if the optional newmask is specified, the cpu list is - * to be changed from effective_xcpus to newmask. Otherwise, effective_xcpus is - * assumed to remain the same. The cpuset should either be a valid or invalid - * partition root. The partition root state may change from valid to invalid - * or vice versa. An error code will be returned if transitioning from - * invalid to valid violates the exclusivity rule. + * to be changed from effective_xcpus to newmask. Otherwise, effective_xcpus + * will be computed and a valid partition will be invalidated if it is the new + * cpumask is empty. The cpuset should either be a valid or invalid partition + * root. The partition root state may change from valid to invalid or vice + * versa. * * For partcmd_invalidate, the current partition will be made invalid. * @@ -1837,7 +1837,6 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, int deleting; /* Deleting cpus from parent's effective_cpus */ int old_prs, new_prs; int part_error = PERR_NONE; /* Partition error? */ - struct cpumask *xcpus = user_xcpus(cs); int parent_prs = parent->partition_root_state; bool nocpu; @@ -1880,30 +1879,30 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, if (!newmask && xcpus_empty(cs)) return PERR_CPUSEMPTY; - nocpu = tasks_nocpu_error(parent, cs, xcpus); + /* + * Except for partcmd_disable and non-NULL newmask, use delmask + * to compute the current effective xcpus value and use it for + * tasks_nocpu_error check. + */ + if ((cmd != partcmd_disable) && !newmask) { + compute_excpus(cs, tmp->delmask); + nocpu = tasks_nocpu_error(parent, cs, tmp->delmask); + } if ((cmd == partcmd_enable) || (cmd == partcmd_enablei)) { - /* - * Need to call compute_excpus() in case - * exclusive_cpus not set. Sibling conflict should only happen - * if exclusive_cpus isn't set. - */ - xcpus = tmp->delmask; - if (compute_excpus(cs, xcpus)) - WARN_ON_ONCE(!cpumask_empty(cs->exclusive_cpus)); new_prs = (cmd == partcmd_enable) ? PRS_ROOT : PRS_ISOLATED; /* * Enabling partition root is not allowed if its * effective_xcpus is empty. */ - if (cpumask_empty(xcpus)) + if (cpumask_empty(tmp->delmask)) return PERR_INVCPUS; - if (prstate_housekeeping_conflict(new_prs, parent_prs, xcpus, NULL)) + if (prstate_housekeeping_conflict(new_prs, parent_prs, tmp->delmask, NULL)) return PERR_HKEEPING; - if (tasks_nocpu_error(parent, cs, xcpus)) + if (nocpu) return PERR_NOCPUS; /* @@ -1915,16 +1914,14 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, * * Warn if it is not the case. */ - cpumask_and(tmp->new_cpus, xcpus, cpu_active_mask); + cpumask_and(tmp->new_cpus, tmp->delmask, cpu_active_mask); WARN_ON_ONCE(!cpumask_subset(tmp->new_cpus, parent->effective_cpus)); - deleting = true; } else if (cmd == partcmd_disable) { /* * May need to add cpus back to parent's effective_cpus * (and maybe removed from subpartitions_cpus/isolated_cpus) - * for valid partition root. xcpus may contain CPUs that - * shouldn't be removed from the two global cpumasks. + * for valid partition root. */ if (is_partition_valid(cs)) { cpumask_copy(tmp->addmask, cs->effective_xcpus); @@ -1944,8 +1941,8 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, goto write_error; } - /* Check newmask again, whether cpus are available for parent/cs */ - nocpu |= tasks_nocpu_error(parent, cs, newmask); + /* Check newmask whether cpus are available for parent/cs */ + nocpu = tasks_nocpu_error(parent, cs, newmask); /* * partcmd_update with newmask: @@ -2000,7 +1997,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, /* * partcmd_update w/o newmask * - * delmask = effective_xcpus & parent->effective_cpus + * delmask = newly computed effective xcpus value * * This can be called from: * 1) update_cpumasks_hier() @@ -2012,7 +2009,7 @@ 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. */ - if (nocpu) { + if (nocpu || cpumask_empty(tmp->delmask)) { part_error = PERR_NOCPUS; if (is_partition_valid(cs)) adding = cpumask_and(tmp->addmask, @@ -2025,38 +2022,44 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, cpumask_copy(tmp->addmask, cs->effective_xcpus); adding = true; } - } else if (is_partition_invalid(cs) && !cpumask_empty(xcpus) && - cpumask_subset(xcpus, parent->effective_xcpus)) { + } else if (is_partition_invalid(cs)) { struct cgroup_subsys_state *css; struct cpuset *child; bool exclusive = true; /* * Convert invalid partition to valid has to pass the - * cpu exclusivity test as well as the housekeeping - * check. + * cpu exclusivity test when cpuset.cpus.exclusive is + * empty as well as the housekeeping check. */ if (prstate_housekeeping_conflict(cs->partition_root_state, - parent_prs, xcpus, NULL)) { + parent_prs, tmp->delmask, NULL)) { part_error = PERR_HKEEPING; goto write_error; } - rcu_read_lock(); - cpuset_for_each_child(child, css, parent) { - if (child == cs) - continue; - if (!cpusets_are_exclusive(cs, child)) { - exclusive = false; - break; + if (cpumask_empty(cs->exclusive_cpus)) { + 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(); } - rcu_read_unlock(); if (exclusive) - deleting = cpumask_and(tmp->delmask, - xcpus, parent->effective_cpus); + deleting = !cpumask_empty(tmp->delmask); else part_error = PERR_NOTEXCL; } + /* + * When both cs and parent remain valid, parent's + * compute_partition_effective_cpumask() call would have removed + * cs's effective_xcpus from the parent's effective_cpus. So + * there is no need to adjust parent's effective_cpus here. + */ } write_error: diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh index 9978c560b398..5824f82fa2b1 100755 --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh @@ -359,6 +359,8 @@ TEST_MATRIX=( A1:P0|A2:P1|A3:P2|B1:P1 2-4|3" " C1-6:P1 C3-6:P1 C5-6:P1 . . P2 . . 0 A1:1-2|A2:3-6|A3:5-6 \ A1:P1|A2:P2|A3:P-1 3-6" + " C1-6:P2 C3-6:P2 C3-4:P2 . . C5-6 . . 0 A1:1-4|A2:5-6|A3:5-6 \ + A1:P2|A2:P2|A3:P-2 1-6" " C1-4:X2-4 C2-4:X3-4:P1 C3-4:X4:P2 \ . . X5 . . 0 A1:1-4|A2:2-4|A3:3-4 \ A1:P0|A2:P-1|A3:P-2 ." @@ -427,6 +429,10 @@ TEST_MATRIX=( # cpuset.cpus is allowed, but those extra CPUs are ignored. " C2-3:P1 C3:P1 . . . C2-4 . . 0 A1:|A2:2-3 A1:P1|A2:P1" + # A child cannot recover until its exclusive CPUs are available again. + " CX1-4:P1 CX3-4:P1 . . X1-2 . . . 0 A1:1-2|A2:1-2|XA2: A1:P1|A2:P-1" + " CX1-4:P1 CX3-4:P1 . . X1-2:X1-4 . . . 0 A1:1-2|A2:3-4|XA2:3-4 A1:P1|A2:P1" + # Taking away all CPUs from parent or itself if there are tasks # will make the partition invalid. " C2-3:P1 C3:P1 . . T C2-3 . . 0 A1:2-3|A2:2-3 A1:P1|A2:P-1" @@ -506,6 +512,11 @@ TEST_MATRIX=( " C1-3:P2 C2:P2 . . . P1 . . 0 A1:1-3|A2:2 A1:P2|A2:P-1 1-3" " C1-3:P2 C2:P1 . . . C2-3 . . 0 A1:1-3|A2:2-3 A1:P2|A2:P-1 1-3" + # A middle isolated parent shrunk below coverage: the released CPUs of + # an invalidated child stay isolated as a higher ancestor still covers them. + " CX0-4:P2 CX2-4:P2 CX3-4:P2 . . X2 . . 0 A1:0-1,3-4|A2:2|A3:2 \ + A1:P2|A2:P2|A3:P-2 0-4" + # # old-A1 old-A2 old-A3 old-B1 new-A1 new-A2 new-A3 new-B1 fail ECPUs Pstate ISOLCPUS # ------ ------ ------ ------ ------ ------ ------ ------ ---- ----- ------ --------