CVE-2026-89759

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.