CVE-2026-89756Medium· 5.5▾ SunlitIn the Linux kernel, the following vulnerability has been resolved: mm/migrate: report RCU-tasks quiescent states in migrate_pages_batch() migrate_pages_batch() unmaps each folio before moving it, and every unmap runs the mmu_notifier …
▾ Sunlit zone — Low / medium · no exploitation signal
impact 30.3 · likelihood 0 · exploitation 0
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Exploit-prediction probability, daily snapshots since Sep 12.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via CVEORG
0.2%
— → 4.7
none → medium
— → 4.7
none → medium
— → 4.7
none → medium
4.7 → 5.5
Last analysed / modified upstream
0.2% → 0.2%
In the Linux kernel, the following vulnerability has been resolved:
mm/migrate: report RCU-tasks quiescent states in migrate_pages_batch()
migrate_pages_batch() unmaps each folio before moving it, and every unmap runs the mmu_notifier invalidate callbacks. On KVM hosts try_to_migrate() ends up in kvm_mmu_notifier_invalidate_range_start() -> tdp_mmu_zap_leafs(), which is expensive, so unmapping a large batch keeps the CPU busy for a long time.
The loop already calls cond_resched(), but on PREEMPTION kernels that is a no-op, and involuntary preemption is not a Tasks-RCU quiescent state.
A long batch therefore never reports a quiescent state, and the migrating task (e.g. kcompactd) becomes a Tasks-RCU holdout, stalling the Tasks-RCU grace period for minutes, which is common at Meta fleet:
INFO: rcu_tasks detected stalls on tasks: 0000000055349ecc: .. nvcsw: 1157401/1157401 holdout: 1 idle_cpu: -1/56 task:kcompactd0 state:R running task Call Trace: tdp_mmu_zap_leafs tdp_mmu_next_root gfn_to_pfn_cache_invalidate_start kvm_mmu_notifier_invalidate_range_start __mmu_notifier_invalidate_range_start try_to_migrate_one try_to_migrate migrate_pages_batch migrate_pages compact_zone compact_node kcompactd kthread
Use cond_resched_tasks_rcu_qs() so a quiescent state is reported even when cond_resched() does nothing.
This has also been discussed at [1]
Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < 8c6d63d434ebb85c6cf3dac1e70a171b183c6614Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < 4757542649af56d894e25e30f57cd497dffad53fLinux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < 4996a7bc01ef35570664854dac2530c604981039Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < 5dc0daff0341c6baba19c38f47d299ac831d7e99Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < 66734981b4d3c105223a13c827c9c73be18d91adLinux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < efe8f86c0916f0f74eea74ae21a3b37f728c6badLinux 3.18Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Field changes observed since this record was first indexed.
Connected by shared product, vendor, weakness, or advisory.
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