CVE-2026-64415 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
mm/swap: add cond_resched() in swap_reclaim_full_clusters to prevent softlockup
We hit a real softlockup in an internal stress test environment. The workload was LTP memory/swap stress on a large arm64 machine, with 320 CPUs, about 1TB memory and an 8.6GB swap device. The system was under heavy load and the swap device had a large number of full clusters. The softlockup was triggered during a stress test after about 3 days.
So, add periodic cond_resched() calls during large full_clusters reclaim operations to prevent softlockup issues.
Detailed call trace as follow:
PID: 3817773 TASK: ffff0883bb28b780 CPU: 48 COMMAND: "kworker/48:7" #0 [ffff800080183d10] __crash_kexec at ffffa4c1361e5de4
#1 [ffff800080183d90] panic at ffffa4c1360d5e9c
#2 [ffff800080183e20] watchdog_timer_fn at ffffa4c136231fa8
... #16 [ffff8000c4ad3cb0] swap_cache_del_folio at ffffa4c1363e1614
#17 [ffff8000c4ad3ce0] __try_to_reclaim_swap at ffffa4c1363e4bfc
#18 [ffff8000c4ad3d40] swap_reclaim_full_clusters at ffffa4c1363e5474
#19 [ffff8000c4ad3da0] swap_reclaim_work at ffffa4c1363e550c
#20 [ffff8000c4ad3dc0] process_one_work at ffffa4c136102edc
#21 [ffff8000c4ad3e10] worker_thread at ffffa4c136103398
#22 [ffff8000c4ad3e70] kthread at ffffa4c13610d95c
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Analysis
by VulDB Data Team • 07/26/2026
The vulnerability addressed in this linux kernel update relates to a potential softlockup condition occurring during memory swap operations, specifically when reclaiming full clusters. This issue manifests in high-load environments where the system maintains extensive swap space with numerous full clusters, creating a scenario where kernel threads become stuck in prolonged execution without yielding control back to the scheduler. The root cause stems from the swap_reclaim_full_clusters function which processes large numbers of full clusters without periodic scheduling interruptions, leading to extended runtime that can exceed the watchdog timer threshold and trigger system lockup conditions.
The technical flaw exists within the memory management subsystem where kernel worker threads executing swap reclaim operations do not incorporate sufficient scheduling points during intensive processing. When dealing with large swap devices containing hundreds or thousands of full clusters under heavy memory pressure, these operations can consume excessive CPU time without calling cond_resched(), which is a critical scheduler primitive that allows other processes to execute and prevents indefinite monopolization of CPU resources. The specific function swap_reclaim_full_clusters operates in a tight loop processing cluster data structures, and without periodic rescheduling, it can hold the CPU for extended periods beyond acceptable limits.
The operational impact of this vulnerability is significant in enterprise environments running large memory systems with substantial swap space configurations. Systems with 320 cpus, 1tb memory, and 8.6gb swap devices under heavy load conditions demonstrate the real-world scenario where this issue can manifest. The stress test environment revealed that softlockups occurred after approximately three days of continuous operation, indicating that this vulnerability is particularly problematic in long-running systems or sustained high-load scenarios. When triggered, such softlockups result in complete system unresponsiveness requiring manual intervention or reboot, potentially causing service disruption and data loss in production environments.
The fix implemented involves adding periodic cond_resched() calls within the swap_reclaim_full_clusters function to ensure proper scheduler cooperation during long-running reclaim operations. This approach directly addresses the scheduling starvation issue by inserting controlled yield points that allow other kernel threads and user processes to execute, preventing any single operation from monopolizing CPU resources for excessive durations. The solution follows established kernel development practices where long-running critical sections must incorporate periodic rescheduling to maintain system responsiveness and prevent watchdog timer violations.
This vulnerability aligns with common weakness enumeration category 1037 which addresses insufficient scheduling in kernel code, and relates to attack technique T1496 in the ATT&CK framework concerning resource exhaustion. The fix demonstrates proper kernel memory management practices as recommended by the linux kernel documentation for preventing scheduler starvation in high-load scenarios. The addition of cond_resched() calls represents a standard mitigation pattern used throughout the kernel to address similar scheduling issues in other subsystems, ensuring that memory management operations remain responsive to system demands while maintaining overall system stability and preventing denial-of-service conditions.
The solution maintains backward compatibility while enhancing system reliability under stress conditions. The periodic rescheduling does not significantly impact performance characteristics since it only introduces minimal overhead during large reclaim operations. This approach provides a robust defense against softlockup conditions without altering the fundamental behavior of memory management functions, making it suitable for production deployment across various hardware configurations and workload patterns.