[PATCH-next 2/6] cgroup/cpuset: Properly compute effective xcpus in update_parent_effective_cpumask()
From: Waiman Long
Date: Wed Oct 21 2026 - 23:18:50 EST
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 and partcmd_invalidate
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().
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 <longman@xxxxxxxxxx>
---
kernel/cgroup/cpuset.c | 36 +++++++++----------
.../selftests/cgroup/test_cpuset_prs.sh | 6 ++++
2 files changed, 22 insertions(+), 20 deletions(-)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 7ead8c3b7974..db6e4663f4be 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1798,7 +1798,6 @@ 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;
@@ -1841,30 +1840,29 @@ 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, use delmask to compute the current
+ * effective xcpus value and use it for tasks_nocpu_error check.
+ */
+ if (cmd != partcmd_disable) {
+ 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;
/*
@@ -1876,9 +1874,8 @@ 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) {
/*
@@ -1973,7 +1970,7 @@ 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,
@@ -1986,8 +1983,7 @@ 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;
@@ -1998,7 +1994,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
* 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;
}
@@ -2014,7 +2010,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
rcu_read_unlock();
if (exclusive)
deleting = cpumask_and(tmp->delmask,
- xcpus, parent->effective_cpus);
+ tmp->delmask, parent->effective_cpus);
else
part_error = PERR_NOTEXCL;
}
diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
index d04aad697b96..47791591002f 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"
--
2.55.0