linux-cve-announce - CVE-2025-40163: sched/deadline: Stop dl

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Message-ID: <2025111227-CVE-2025-40163-55e0@gregkh>
Date: Wed, 12 Nov 2025 19:26:29 +0900
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40163: sched/deadline: Stop dl_server before CPU goes offline

From: Greg Kroah-Hartman <gregkh@...nel.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/8218e149-7718-4432-9312-f97297c352b9@linux.ibm.com/
[2]: https://github.com/ibm-power-utilities/powerpc-utils/tree/next/src/drmgr

[sshegde: wrote the changelog and tested it]

The Linux kernel CVE team has assigned CVE-2025-40163 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.17 with commit 4ae8d9aa9f9dc7137ea5e564d79c5aa5af1bc45c and fixed in 6.17.5 with commit ab6c0f158508bb16d483add70b73a73f95651c33
	Issue introduced in 6.17 with commit 4ae8d9aa9f9dc7137ea5e564d79c5aa5af1bc45c and fixed in 6.18-rc2 with commit ee6e44dfe6e50b4a5df853d933a96bdff5309e6e

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-40163
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	kernel/sched/core.c
	kernel/sched/deadline.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/ab6c0f158508bb16d483add70b73a73f95651c33
	https://git.kernel.org/stable/c/ee6e44dfe6e50b4a5df853d933a96bdff5309e6e