linux-kernel - Re: [PATCH -next] cpuset: fix warning when disabling remote partition

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Message-ID: <5cbfe54e-846a-4303-bb34-3a7b64a174f3@huaweicloud.com>
Date: Wed, 17 Dec 2025 09:10:07 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: longman@...hat.com, tj@...nel.org, hannes@...xchg.org, mkoutny@...e.com
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
 lujialin4@...wei.com, chenridong@...wei.com
Subject: Re: [PATCH -next] cpuset: fix warning when disabling remote partition



On 2025/11/27 11:04, Chen Ridong wrote:
> From: Chen Ridong <chenridong@...wei.com>
> 
> 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:
>  <TASK>
>  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: 4449b1ce46bf ("cgroup/cpuset: Remove remote_partition_check() & make update_cpumasks_hier() handle remote partition")

Fixes: f62a5d39368e ("cgroup/cpuset: Remove remote_partition_check() & make update_cpumasks_hier()
handle remote partition")

Apologies, the correct fixes commit id should be f62a5d39368e. The earlier one might be from stale
code in my local repository.

Tj, could you please update the commit ID when applying this patch?

> Signed-off-by: Chen Ridong <chenridong@...wei.com>
> ---
>  kernel/cgroup/cpuset.c | 21 ++++++++++++++++-----
>  1 file changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index fea577b4016a..fbe539d66d9b 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1648,7 +1648,14 @@ 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;
> @@ -3956,8 +3963,9 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
>  	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);
> @@ -3970,9 +3978,12 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
>  	 * 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

-- 
Best regards,
Ridong