From aa7d3a56a20f07978d9f401e13637a6479b13bd0 Mon Sep 17 00:00:00 2001 From: Chen Ridong Date: Thu, 18 Dec 2025 01:59:50 +0000 Subject: cpuset: fix warning when disabling remote partition A warning was triggered as follows: WARNING: kernel/cgroup/cpuset.c:1651 at remote_partition_disable+0xf7/0x110 RIP: 0010:remote_partition_disable+0xf7/0x110 RSP: 0018:ffffc90001947d88 EFLAGS: 00000206 RAX: 0000000000007fff RBX: ffff888103b6e000 RCX: 0000000000006f40 RDX: 0000000000006f00 RSI: ffffc90001947da8 RDI: ffff888103b6e000 RBP: ffff888103b6e000 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000001 R11: ffff88810b2e2728 R12: ffffc90001947da8 R13: 0000000000000000 R14: ffffc90001947da8 R15: ffff8881081f1c00 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f55c8bbe0b2 CR3: 000000010b14c000 CR4: 00000000000006f0 Call Trace: update_prstate+0x2d3/0x580 cpuset_partition_write+0x94/0xf0 kernfs_fop_write_iter+0x147/0x200 vfs_write+0x35d/0x500 ksys_write+0x66/0xe0 do_syscall_64+0x6b/0x390 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7f55c8cd4887 Reproduction steps (on a 16-CPU machine): # cd /sys/fs/cgroup/ # mkdir A1 # echo +cpuset > A1/cgroup.subtree_control # echo "0-14" > A1/cpuset.cpus.exclusive # mkdir A1/A2 # echo "0-14" > A1/A2/cpuset.cpus.exclusive # echo "root" > A1/A2/cpuset.cpus.partition # echo 0 > /sys/devices/system/cpu/cpu15/online # echo member > A1/A2/cpuset.cpus.partition When CPU 15 is offlined, subpartitions_cpus gets cleared because no CPUs remain available for the top_cpuset, forcing partitions to share CPUs with the top_cpuset. In this scenario, disabling the remote partition triggers a warning stating that effective_xcpus is not a subset of subpartitions_cpus. Partitions should be invalidated in this case to inform users that the partition is now invalid(cpus are shared with top_cpuset). To fix this issue: 1. Only emit the warning only if subpartitions_cpus is not empty and the effective_xcpus is not a subset of subpartitions_cpus. 2. During the CPU hotplug process, invalidate partitions if subpartitions_cpus is empty. Fixes: f62a5d39368e ("cgroup/cpuset: Remove remote_partition_check() & make update_cpumasks_hier() handle remote partition") Signed-off-by: Chen Ridong Reviewed-by: Waiman Long Signed-off-by: Tejun Heo --- kernel/cgroup/cpuset.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) (limited to 'kernel') diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 6e6eb09b8db6..3e8cc34d8d50 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1668,7 +1668,14 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs, static void remote_partition_disable(struct cpuset *cs, struct tmpmasks *tmp) { WARN_ON_ONCE(!is_remote_partition(cs)); - WARN_ON_ONCE(!cpumask_subset(cs->effective_xcpus, subpartitions_cpus)); + /* + * When a CPU is offlined, top_cpuset may end up with no available CPUs, + * which should clear subpartitions_cpus. We should not emit a warning for this + * scenario: the hierarchy is updated from top to bottom, so subpartitions_cpus + * may already be cleared when disabling the partition. + */ + WARN_ON_ONCE(!cpumask_subset(cs->effective_xcpus, subpartitions_cpus) && + !cpumask_empty(subpartitions_cpus)); spin_lock_irq(&callback_lock); cs->remote_partition = false; @@ -3976,8 +3983,9 @@ retry: if (remote || (is_partition_valid(cs) && is_partition_valid(parent))) compute_partition_effective_cpumask(cs, &new_cpus); - if (remote && cpumask_empty(&new_cpus) && - partition_is_populated(cs, NULL)) { + if (remote && (cpumask_empty(subpartitions_cpus) || + (cpumask_empty(&new_cpus) && + partition_is_populated(cs, NULL)))) { cs->prs_err = PERR_HOTPLUG; remote_partition_disable(cs, tmp); compute_effective_cpumask(&new_cpus, cs, parent); @@ -3990,9 +3998,12 @@ retry: * 1) empty effective cpus but not valid empty partition. * 2) parent is invalid or doesn't grant any cpus to child * partitions. + * 3) subpartitions_cpus is empty. */ - if (is_local_partition(cs) && (!is_partition_valid(parent) || - tasks_nocpu_error(parent, cs, &new_cpus))) + if (is_local_partition(cs) && + (!is_partition_valid(parent) || + tasks_nocpu_error(parent, cs, &new_cpus) || + cpumask_empty(subpartitions_cpus))) partcmd = partcmd_invalidate; /* * On the other hand, an invalid partition root may be transitioned -- cgit v1.2.3