CVE-2025-40163
Deferred Deferred - Pending Action
BaseFortify

Publication date: 2025-11-12

Last updated on: 2026-06-01

Assigner: kernel.org

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]
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Meta Information
Published
2025-11-12
Last Modified
2026-06-01
Generated
2026-06-16
AI Q&A
2025-11-13
EPSS Evaluated
2026-06-15
NVD
CVE-2025-40163
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *
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Exploitability
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CWE ID Description
CWE-UNKNOWN
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Mitigation Strategies

To mitigate this vulnerability, ensure that the Linux kernel is updated to include the fix that stops the dl_server before the CPU goes offline. This fix prevents the hrtimer from firing after the CPU is removed. Avoid running CPU removal operations that trigger this issue until the kernel is patched.

Executive Summary

This vulnerability occurs in the Linux kernel's CPU scheduler deadline code. When a CPU is being taken offline, a high-resolution timer (dl_server hrtimer) related to deadline scheduling can still be active and fire after the CPU is removed from the system. This causes a kernel warning and potentially unstable behavior because the timer callback runs on a CPU that is no longer present. The fix involves stopping the dl_server timer before the CPU is marked offline to prevent this race condition.

Impact Analysis

This vulnerability can cause kernel warnings and potentially unstable or unpredictable behavior during CPU removal operations. It may lead to system instability or crashes when CPUs are taken offline dynamically, affecting system reliability and uptime.

Detection Guidance

This vulnerability can be detected by observing kernel warnings related to the CPU removal operation, specifically warnings like: "WARNING: CPU: 0 PID: 0 at kernel/sched/cpudeadline.c:219 cpudl_set+0x58/0x170". You can monitor the kernel log for such warnings using commands like 'dmesg | grep cpudl_set' or 'journalctl -k | grep cpudl_set'. Additionally, running the CPU removal command 'drmgr -c cpu -r -q 1' may reproduce the warning if the system is vulnerable.

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