CVE-2026-89759
Low risk· EPSS 8%Exploitation Probability (EPSS)
Low risk8th percentile - higher than 8% of all known CVEs
Summary
In the Linux kernel, a vulnerability was fixed in the kmemleak module where kmemleak_scan() scanned all task stacks under a single RCU read-side critical section with no reschedule point. On hosts with very many threads, this could hog a CPU and trip the soft lockup watchdog. The fix walks tasks one PID at a time using find_ge_pid() and releases the RCU lock between tasks.
Risk Assessment
On systems with a very large number of threads (especially debug builds with KASAN/lockdep), kmemleak scanning can block a CPU for over 20 seconds, causing false watchdog alarms and temporary service unavailability.
Recommendation
Update the Linux kernel to a version containing this fix (the 3-patch mm/kmemleak series). If updating is not possible, consider disabling kmemleak in the kernel configuration on hosts with very many threads.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS