In the Linux kernel, the following vulnerability has been resolved:

mm/kmemleak: avoid soft lockup when scanning task stacks

Patch series "mm/kmemleak: avoid soft lockup when scanning task", v3.

kmemleak_scan() scans every task stack under one rcu_read_lock() with no
reschedule point, which can trip the soft lockup watchdog on hosts with
very many threads.

That prints the following message, depending on the workload+host
configuration:

watchdog: BUG: soft lockup - CPU#35 stuck for 22s! [kmemleak:537]
scan_block
kmemleak_scan
kmemleak_scan_thread
kthread

Patch 1 walks the tasks with find_ge_pid() so the scan reschedules between
tasks

Patches 2-3 let the scan loops stop early once a scan is interrupted.


This patch (of 3):

kmemleak_scan() walks every thread and scans its kernel stack under a
single rcu_read_lock() with no reschedule point. On a host with very many
threads -- amplified by KASAN/lockdep in debug builds -- this loop can hog
a CPU long enough to trip the soft lockup watchdog:

watchdog: BUG: soft lockup - CPU#35 stuck for 22s! [kmemleak:537]
scan_block
kmemleak_scan
kmemleak_scan_thread
kthread

A cond_resched() cannot be added directly: the loop runs inside an RCU
read-side critical section.

Walk the tasks one PID at a time with find_ge_pid(), taking the RCU read
lock only to look up and pin each task. The stack is then scanned with no
lock held, so cond_resched() runs between tasks and the scan stops early
on scan_should_stop(). This follows the next_tgid()/task_seq_get_next()
iteration pattern and keeps each RCU critical section short.

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Advisories
Source ID Title
Debian DLA Debian DLA DLA-4817-1 linux-6.12 security update
Debian DSA Debian DSA DSA-6528-1 linux security update
Fixes

Solution

No solution given by the vendor.


Workaround

No workaround given by the vendor.

History

Wed, 21 Oct 2026 13:15:00 +0000


Sat, 12 Sep 2026 17:00:00 +0000

Type Values Removed Values Added
Weaknesses CWE-770

Sat, 12 Sep 2026 12:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-1050
References
Metrics threat_severity

None

cvssV3_1

{'score': 4.7, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Moderate


Sat, 12 Sep 2026 08:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-770

Fri, 11 Sep 2026 23:45:00 +0000

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: mm/kmemleak: avoid soft lockup when scanning task stacks Patch series "mm/kmemleak: avoid soft lockup when scanning task", v3. kmemleak_scan() scans every task stack under one rcu_read_lock() with no reschedule point, which can trip the soft lockup watchdog on hosts with very many threads. That prints the following message, depending on the workload+host configuration: watchdog: BUG: soft lockup - CPU#35 stuck for 22s! [kmemleak:537] scan_block kmemleak_scan kmemleak_scan_thread kthread Patch 1 walks the tasks with find_ge_pid() so the scan reschedules between tasks Patches 2-3 let the scan loops stop early once a scan is interrupted. This patch (of 3): kmemleak_scan() walks every thread and scans its kernel stack under a single rcu_read_lock() with no reschedule point. On a host with very many threads -- amplified by KASAN/lockdep in debug builds -- this loop can hog a CPU long enough to trip the soft lockup watchdog: watchdog: BUG: soft lockup - CPU#35 stuck for 22s! [kmemleak:537] scan_block kmemleak_scan kmemleak_scan_thread kthread A cond_resched() cannot be added directly: the loop runs inside an RCU read-side critical section. Walk the tasks one PID at a time with find_ge_pid(), taking the RCU read lock only to look up and pin each task. The stack is then scanned with no lock held, so cond_resched() runs between tasks and the scan stops early on scan_should_stop(). This follows the next_tgid()/task_seq_get_next() iteration pattern and keeps each RCU critical section short.
Title mm/kmemleak: avoid soft lockup when scanning task stacks
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-10-21T12:48:36.907Z

Reserved: 2026-09-11T19:38:34.763Z

Link: CVE-2026-89759

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-11T20:20:06.997

Modified: 2026-10-21T13:20:25.110

Link: CVE-2026-89759

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-09-11T19:47:01Z

Links: CVE-2026-89759 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-09-15T19:15:16Z

Weaknesses