CVE-2026-89759

Summary

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.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/9a1b12c06c192290b8479de48f66f1e75d89c4b7
• https://git.kernel.org/stable/c/3fc8044251de21555fb02c365fa681bab8b0db55
• https://git.kernel.org/stable/c/1838c704bcb4fd3556cf67513c6f97a39099e35c
• https://git.kernel.org/stable/c/5d10d4e19e6daa487f0cd0ea6cba472325de92f9

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