linux-toradex.git/kernel/cgroup/cpuset.c, branch v7.1

cgroup/cpuset: Use effective_xcpus in partcmd_update add/del mask calculation

2026-05-27T18:58:59+00:00

When sibling CPU exclusion occurs, a partition's user_xcpus may contain
CPUs that were never actually granted to it. These CPUs are present in
user_xcpus(cs) but not in cs->effective_xcpus.

The partcmd_update path in update_parent_effective_cpumask() uses
user_xcpus(cs) (via the local variable xcpus) to compute the addmask
(CPUs to return to parent) and delmask (CPUs to request from parent).
This is incorrect:

 1) When newmask removes a CPU that was previously excluded by a
    sibling, addmask incorrectly includes that CPU and tries to return
    it to the parent even though the partition never actually owned it,
    causing CPU overlap with sibling partitions and triggering warnings
    in generate_sched_domains().

 2) When newmask adds a previously excluded CPU that is now available,
    delmask fails to request it from the parent because user_xcpus(cs)
    already includes it.

Fix this by using cs->effective_xcpus instead of user_xcpus(cs) in all
partcmd_update paths that calculate addmask or delmask, including the
PERR_NOCPUS error handling paths.

Reproducers:

  Example 1 - Removing a sibling-excluded CPU incorrectly returns it:

    # cd /sys/fs/cgroup
    # echo "0-1" > a1/cpuset.cpus
    # echo "root" > a1/cpuset.cpus.partition
    # echo "0-2" > b1/cpuset.cpus
    # echo "root" > b1/cpuset.cpus.partition
    # echo "2" > b1/cpuset.cpus
    # cat cpuset.cpus.effective
    # Actual: 0-1,3    Expected: 3

  Example 2 - Expanding to a previously excluded CPU fails to request it:

    # cd /sys/fs/cgroup
    # echo "0-1" > a1/cpuset.cpus
    # echo "root" > a1/cpuset.cpus.partition
    # echo "0-2" > b1/cpuset.cpus
    # echo "root" > b1/cpuset.cpus.partition
    # echo "member" > a1/cpuset.cpus.partition
    # echo "1-2" > b1/cpuset.cpus
    # cat cpuset.cpus.effective
    # Actual: 0-1,3    Expected: 0,3

Fixes: 2a3602030d80 ("cgroup/cpuset: Don't invalidate sibling partitions on cpuset.cpus conflict")
Cc: stable@vger.kernel.org # v7.0+
Suggested-by: Zhang Guopeng 
Signed-off-by: Sun Shaojie 
Reviewed-by: Waiman Long 
Signed-off-by: Tejun Heo

cgroup/cpuset: Return only actually allocated CPUs during partition invalidation

2026-05-13T18:54:53+00:00

In update_parent_effective_cpumask() with partcmd_invalidate, the CPUs
to return to the parent are computed as:

    adding = cpumask_and(tmp->addmask, xcpus, parent->effective_xcpus);

where xcpus = user_xcpus(cs) which returns cs->exclusive_cpus (if set)
or cs->cpus_allowed. When exclusive_cpus is not set, user_xcpus(cs) can
contain CPUs that were never actually granted to the partition due to
sibling exclusion in compute_excpus(). Consequently, the invalidation
may return CPUs to the parent that remain in use by sibling partitions,
causing overlapping effective_cpus and triggering the
WARN_ON_ONCE(1) in generate_sched_domains().

Use cs->effective_xcpus instead, which reflects the CPUs actually
granted to this partition.

Reproducer (on a 4-CPU machine):

    cd /sys/fs/cgroup
    mkdir a1 b1

    # a1 becomes partition root with CPUs 0-1
    echo "0-1" > a1/cpuset.cpus
    echo "root" > a1/cpuset.cpus.partition

    # b1 becomes partition root with CPUs 1-2, but sibling exclusion
    # reduces its effective_xcpus to CPU 2 only
    echo "1-2" > b1/cpuset.cpus
    echo "root" > b1/cpuset.cpus.partition

    # b1 changes cpus_allowed to 0-1 -> partition invalidation
    echo "0-1" > b1/cpuset.cpus

    # Expected: CPUs 2-3  (only CPU 2 returned from b1)
    # Actual:   CPUs 1-3  (CPU 0-1 returned, overlapping with a1)
    cat cpuset.cpus.effective

dmesg will also show a WARNING from generate_sched_domains() reporting
overlapping partition root effective_cpus.

Fixes: 2a3602030d80 ("cgroup/cpuset: Don't invalidate sibling partitions on cpuset.cpus conflict")
Cc: stable@vger.kernel.org # v7.0+
Signed-off-by: sunshaojie 
Tested-by: Chen Ridong 
Reviewed-by: Chen Ridong 
Reviewed-by: Waiman Long 
Signed-off-by: Tejun Heo

cgroup/cpuset: Reserve DL bandwidth only for root-domain moves

2026-05-11T20:27:14+00:00

cpuset_can_attach() currently adds the bandwidth of all migrating
SCHED_DEADLINE tasks to sum_migrate_dl_bw. If the source and destination
cpuset effective CPU masks do not overlap, the whole sum is then
reserved in the destination root domain.

set_cpus_allowed_dl(), however, subtracts bandwidth from the source
root domain only when the affinity change really moves the task between
root domains. A DL task can move between cpusets that are still in the
same root domain, so including that task in sum_migrate_dl_bw can reserve
destination bandwidth without a matching source-side subtraction.

Share the root-domain move test with set_cpus_allowed_dl(). Keep
nr_migrate_dl_tasks counting all migrating deadline tasks for cpuset DL
task accounting, but add to sum_migrate_dl_bw only for tasks that need a
root-domain bandwidth move. Keep using the destination cpuset effective
CPU mask and leave the broader can_attach()/attach() transaction model
unchanged.

Fixes: 2ef269ef1ac0 ("cgroup/cpuset: Free DL BW in case can_attach() fails")
Cc: stable@vger.kernel.org # v6.10+
Signed-off-by: Guopeng Zhang 
Reviewed-by: Waiman Long 
Acked-by: Juri Lelli 
Tested-by: Juri Lelli 
Signed-off-by: Tejun Heo

cgroup/cpuset: Reset DL migration state on can_attach() failure

2026-05-11T08:14:49+00:00

cpuset_can_attach() accumulates temporary SCHED_DEADLINE migration
state in the destination cpuset while walking the taskset.

If a later task_can_attach() or security_task_setscheduler() check
fails, cgroup_migrate_execute() treats cpuset as the failing subsystem
and does not call cpuset_cancel_attach() for it. The partially
accumulated state is then left behind and can be consumed by a later
attach, corrupting cpuset DL task accounting and pending DL bandwidth
accounting.

Reset the pending DL migration state from the common error exit when
ret is non-zero. Successful can_attach() keeps the state for
cpuset_attach() or cpuset_cancel_attach().

Fixes: 2ef269ef1ac0 ("cgroup/cpuset: Free DL BW in case can_attach() fails")
Cc: stable@vger.kernel.org # v6.10+
Signed-off-by: Guopeng Zhang 
Signed-off-by: Tejun Heo 
Reviewed-by: Chen Ridong 
Reviewed-by: Waiman Long

cgroup/cpuset: move PF_EXITING check before __GFP_HARDWALL in cpuset_current_node_allowed()

2026-05-07T21:57:31+00:00

Since prepare_alloc_pages() unconditionally adds __GFP_HARDWALL for the
fast path when cpusets are enabled, the __GFP_HARDWALL check in
cpuset_current_node_allowed() causes the PF_EXITING escape path to be
skipped on the first allocation attempt.  This makes it unreachable in
the common case, so dying tasks can get stuck in direct reclaim or even
trigger OOM while trying to exit, despite being allowed to allocate from
any node.

Move the PF_EXITING check before __GFP_HARDWALL so that dying tasks
can allocate memory from any node to exit quickly, even when cpusets
are enabled.

Also update the function comment to reflect the actual behavior of
prepare_alloc_pages() and the corrected check ordering.

Signed-off-by: Chen Wandun 
Acked-by: Michal Koutný 
Acked-by: Waiman Long 
Signed-off-by: Tejun Heo

cgroup/cpuset: record DL BW alloc CPU for attach rollback

2026-04-17T18:57:37+00:00

cpuset_can_attach() allocates DL bandwidth only when migrating
deadline tasks to a disjoint CPU mask, but cpuset_cancel_attach()
rolls back based only on nr_migrate_dl_tasks. This makes the DL
bandwidth alloc/free paths asymmetric: rollback can call dl_bw_free()
even when no dl_bw_alloc() was done.

Rollback also needs to undo the reservation against the same CPU/root
domain that was charged. Record the CPU used by dl_bw_alloc() and use
that state in cpuset_cancel_attach(). If no allocation happened,
dl_bw_cpu stays at -1 and rollback skips dl_bw_free(). If allocation
did happen, bandwidth is returned to the same CPU/root domain.

Successful attach paths are unchanged. This only fixes failed attach
rollback accounting.

Fixes: 2ef269ef1ac0 ("cgroup/cpuset: Free DL BW in case can_attach() fails")
Signed-off-by: Guopeng Zhang 
Reviewed-by: Waiman Long 
Signed-off-by: Tejun Heo

cgroup/cpuset: Skip security check for hotplug induced v1 task migration

2026-03-31T19:14:13+00:00

When a CPU hot removal causes a v1 cpuset to lose all its CPUs, the
cpuset hotplug handler will schedule a work function to migrate tasks
in that cpuset with no CPU to its ancestor to enable those tasks to
continue running.

If a strict security policy is in place, however, the task migration
may fail when security_task_setscheduler() call in cpuset_can_attach()
returns a -EACCES error. That will mean that those tasks will have
no CPU to run on. The system administrators will have to explicitly
intervene to either add CPUs to that cpuset or move the tasks elsewhere
if they are aware of it.

This problem was found by a reported test failure in the LTP's
cpuset_hotplug_test.sh. Fix this problem by treating this special case as
an exception to skip the setsched security check in cpuset_can_attach()
when a v1 cpuset with tasks have no CPU left.

With that patch applied, the cpuset_hotplug_test.sh test can be run
successfully without failure.

Signed-off-by: Waiman Long 
Signed-off-by: Tejun Heo

cgroup/cpuset: Simplify setsched decision check in task iteration loop of cpuset_can_attach()

2026-03-31T19:14:13+00:00

Centralize the check required to run security_task_setscheduler() in
the task iteration loop of cpuset_can_attach() outside of the loop as
it has no dependency on the characteristics of the tasks themselves.

There is no functional change.

Signed-off-by: Waiman Long 
Signed-off-by: Tejun Heo

cgroup/cpuset: Call rebuild_sched_domains() directly in hotplug

2026-03-06T16:58:25+00:00

Besides deferring the call to housekeeping_update(), commit 6df415aa46ec
("cgroup/cpuset: Defer housekeeping_update() calls from CPU hotplug
to workqueue") also defers the rebuild_sched_domains() call to
the workqueue. So a new offline CPU may still be in a sched domain
or new online CPU not showing up in the sched domains for a short
transition period. That could be a problem in some corner cases and
can be the cause of a reported test failure[1]. Fix it by calling
rebuild_sched_domains_cpuslocked() directly in hotplug as before. If
isolated partition invalidation or recreation is being done, the
housekeeping_update() call to update the housekeeping cpumasks will
still be deferred to a workqueue.

In commit 3bfe47967191 ("cgroup/cpuset: Move
housekeeping_update()/rebuild_sched_domains() together"),
housekeeping_update() is called before rebuild_sched_domains() because
it needs to access the HK_TYPE_DOMAIN housekeeping cpumask. That is now
changed to use the static HK_TYPE_DOMAIN_BOOT cpumask as HK_TYPE_DOMAIN
cpumask is now changeable at run time.  As a result, we can move the
rebuild_sched_domains() call before housekeeping_update() with
the slight advantage that it will be done in the same cpus_read_lock
critical section without the possibility of interference by a concurrent
cpu hot add/remove operation.

As it doesn't make sense to acquire cpuset_mutex/cpuset_top_mutex after
calling housekeeping_update() and immediately release them again, move
the cpuset_full_unlock() operation inside update_hk_sched_domains()
and rename it to cpuset_update_sd_hk_unlock() to signify that it will
release the full set of locks.

[1] https://lore.kernel.org/lkml/1a89aceb-48db-4edd-a730-b445e41221fe@nvidia.com

Fixes: 6df415aa46ec ("cgroup/cpuset: Defer housekeeping_update() calls from CPU hotplug to workqueue")
Tested-by: Jon Hunter 
Reviewed-by: Chen Ridong 
Signed-off-by: Waiman Long 
Signed-off-by: Tejun Heo

Merge tag 'cgroup-for-7.0-rc2-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

2026-03-03T22:25:18+00:00

Pull cgroup fixes from Tejun Heo:

 - Fix circular locking dependency in cpuset partition code by
   deferring housekeeping_update() calls to a workqueue instead
   of calling them directly under cpus_read_lock

 - Fix null-ptr-deref in rebuild_sched_domains_cpuslocked() when
   generate_sched_domains() returns NULL due to kmalloc failure

 - Fix incorrect cpuset behavior for effective_xcpus in
   partition_xcpus_del() and cpuset_update_tasks_cpumask()
   in update_cpumasks_hier()

 - Fix race between task migration and cgroup iteration

* tag 'cgroup-for-7.0-rc2-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup/cpuset: fix null-ptr-deref in rebuild_sched_domains_cpuslocked
  cgroup/cpuset: Call housekeeping_update() without holding cpus_read_lock
  cgroup/cpuset: Defer housekeeping_update() calls from CPU hotplug to workqueue
  cgroup/cpuset: Move housekeeping_update()/rebuild_sched_domains() together
  kselftest/cgroup: Simplify test_cpuset_prs.sh by removing "S+" command
  cgroup/cpuset: Set isolated_cpus_updating only if isolated_cpus is changed
  cgroup/cpuset: Clarify exclusion rules for cpuset internal variables
  cgroup/cpuset: Fix incorrect use of cpuset_update_tasks_cpumask() in update_cpumasks_hier()
  cgroup/cpuset: Fix incorrect change to effective_xcpus in partition_xcpus_del()
  cgroup: fix race between task migration and iteration