CVE-2025-40163 sched/deadline: Stop dl_server before CPU goes offline
A race condition in the Linux kernel scheduler can trigger a warning and potential instability when a CPU is taken offline, requiring local administrative access to exploit.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40163?
CVE-2025-40163 is a vulnerability in Linux, published on 12 Nov 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
sched/deadline: Stop dl_server before CPU goes offline
IBM CI tool reported kernel warning[1] when running a CPU removal operation through drmgr[2]. i.e "drmgr -c cpu -r -q 1"
WARNING: CPU: 0 PID: 0 at kernel/sched/cpudeadline.c:219 cpudl_set+0x58/0x170 NIP [c0000000002b6ed8] cpudl_set+0x58/0x170 LR [c0000000002b7cb8] dl_server_timer+0x168/0x2a0 Call Trace: [c000000002c2f8c0] init_stack+0x78c0/0x8000 (unreliable) [c0000000002b7cb8] dl_server_timer+0x168/0x2a0 [c00000000034df84] __hrtimer_run_queues+0x1a4/0x390 [c00000000034f624] hrtimer_interrupt+0x124/0x300 [c00000000002a230] timer_interrupt+0x140/0x320
Git bisects to: commit 4ae8d9aa9f9d ("sched/deadline: Fix dl_server getting stuck")
This happens since: - dl_server hrtimer gets enqueued close to cpu offline, when kthread_park enqueues a fair task. - CPU goes offline and drmgr removes it from cpu_present_mask. - hrtimer fires and warning is hit.
Fix it by stopping the dl_server before CPU is marked dead.
[1]: https://lore.kernel.org/all/[email protected]/ [2]: https://github.com/ibm-power-utilities/powerpc-utils/tree/next/src/drmgr
[sshegde: wrote the changelog and tested it]
Which versions are affected by CVE-2025-40163?
How do I fix CVE-2025-40163?
Apply the vendor's patch.
Is CVE-2025-40163 being exploited?
There is no known exploitation of CVE-2025-40163 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40163, GHSA-v7xp-46vw-cxcp, UBUNTU-CVE-2025-40163.