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cpuset: fix overlap of partition effective CPUs

A warning was detect:

WARNING: kernel/cgroup/cpuset.c:825 at rebuild_sched_domains_locked
Modules linked in:
CPU: 12 UID: 0 PID: 681 Comm: rmdir 6.19.0-rc6-next-20260121+
RIP: 0010:rebuild_sched_domains_locked+0x309/0x4b0
RSP: 0018:ffffc900019bbd28 EFLAGS: 00000202
RAX: ffff888104413508 RBX: 0000000000000008 RCX: ffff888104413510
RDX: ffff888109b5f400 RSI: 000000000000ffcf RDI: 0000000000000001
RBP: 0000000000000002 R08: ffff888104413508 R09: 0000000000000002
R10: ffff888104413508 R11: 0000000000000001 R12: ffff888104413500
R13: 0000000000000002 R14: ffffc900019bbd78 R15: 0000000000000000
FS: 00007fe274b8d740(0000) GS:ffff8881b6b3c000(0000) knlGS:
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fe274c98b50 CR3: 00000001047a9000 CR4: 00000000000006f0
Call Trace:
<TASK>
update_prstate+0x1c7/0x580
cpuset_css_killed+0x2f/0x50
kill_css+0x32/0x180
cgroup_destroy_locked+0xa7/0x200
cgroup_rmdir+0x28/0x100
kernfs_iop_rmdir+0x4c/0x80
vfs_rmdir+0x12c/0x280
filename_rmdir+0x19e/0x200
__x64_sys_rmdir+0x23/0x40
do_syscall_64+0x6b/0x390

It can be reproduced by steps:

# cd /sys/fs/cgroup/
# mkdir A1
# mkdir B1
# mkdir C1
# echo 1-3 > A1/cpuset.cpus
# echo root > A1/cpuset.cpus.partition
# echo 3-5 > B1/cpuset.cpus
# echo root > B1/cpuset.cpus.partition
# echo 6 > C1/cpuset.cpus
# echo root > C1/cpuset.cpus.partition
# rmdir A1/
# rmdir C1/

Both A1 and B1 were initially configured with CPU 3, which was exclusively
assigned to A1's partition. When A1 was removed, CPU 3 was returned to the
root pool. However, B1 incorrectly regained access to CPU 3 when
update_cpumasks_hier was triggered during C1's removal, which also updated
sibling configurations.

The update_sibling_cpumasks function was called to synchronize siblings'
effective CPUs due to changes in their parent's effective CPUs. However,
parent effective CPU changes should not affect partition-effective CPUs.

To fix this issue, update_cpumasks_hier should only be invoked when the
sibling is not a valid partition in the update_sibling_cpumasks.

Fixes: 2a3602030d80 ("cgroup/cpuset: Don't invalidate sibling partitions on cpuset.cpus conflict")
Signed-off-by: Chen Ridong <chenridong@huawei.com>
Reviewed-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

authored by

Chen Ridong and committed by
Tejun Heo 8b1f3c54 5eab8c58

+6 -13
+6 -13
kernel/cgroup/cpuset.c
··· 2222 2222 * It is possible a change in parent's effective_cpus 2223 2223 * due to a change in a child partition's effective_xcpus will impact 2224 2224 * its siblings even if they do not inherit parent's effective_cpus 2225 - * directly. 2225 + * directly. It should not impact valid partition. 2226 2226 * 2227 2227 * The update_cpumasks_hier() function may sleep. So we have to 2228 2228 * release the RCU read lock before calling it. 2229 2229 */ 2230 2230 rcu_read_lock(); 2231 2231 cpuset_for_each_child(sibling, pos_css, parent) { 2232 - if (sibling == cs) 2232 + if (sibling == cs || is_partition_valid(sibling)) 2233 2233 continue; 2234 - if (!is_partition_valid(sibling)) { 2235 - compute_effective_cpumask(tmp->new_cpus, sibling, 2236 - parent); 2237 - if (cpumask_equal(tmp->new_cpus, sibling->effective_cpus)) 2238 - continue; 2239 - } else if (is_remote_partition(sibling)) { 2240 - /* 2241 - * Change in a sibling cpuset won't affect a remote 2242 - * partition root. 2243 - */ 2234 + 2235 + compute_effective_cpumask(tmp->new_cpus, sibling, 2236 + parent); 2237 + if (cpumask_equal(tmp->new_cpus, sibling->effective_cpus)) 2244 2238 continue; 2245 - } 2246 2239 2247 2240 if (!css_tryget_online(&sibling->css)) 2248 2241 continue;