CVE-2026-89759 in Linux
Summary
by MITRE • 09/11/2026
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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