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cgroup/cpuset: Properly compute effective xcpus in update_parent_effective_cpumask()

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Since the introduction of cpuset.cpus.exclusive in commit
e2ffe502ba ("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: e2ffe502ba ("cgroup/cpuset: Add cpuset.cpus.exclusive for v2")
Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
Tested-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Waiman Long 2026-10-25 17:44:40 -04:00 committed by Tejun Heo
parent 0bce85ff2c
commit 69a75e4f37
2 changed files with 56 additions and 42 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

87
kernel/cgroup/cpuset.c
View File

@ -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:

11
tools/testing/selftests/cgroup/test_cpuset_prs.sh
View File

@ -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
# ------ ------ ------ ------ ------ ------ ------ ------ ---- ----- ------ --------