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CVE-2026-89756 (GCVE-0-2026-89756)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:46 – Updated: 2026-09-14 12:02
VLAI
Title
mm/migrate: report RCU-tasks quiescent states in migrate_pages_batch()
Summary
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]
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 8315f42295d2667a7f942f154b73a86fd7cb2227 , < 8c6d63d434ebb85c6cf3dac1e70a171b183c6614 (git)
Affected: 8315f42295d2667a7f942f154b73a86fd7cb2227 , < 4757542649af56d894e25e30f57cd497dffad53f (git)
Affected: 8315f42295d2667a7f942f154b73a86fd7cb2227 , < 4996a7bc01ef35570664854dac2530c604981039 (git)
Affected: 8315f42295d2667a7f942f154b73a86fd7cb2227 , < 5dc0daff0341c6baba19c38f47d299ac831d7e99 (git)
Affected: 8315f42295d2667a7f942f154b73a86fd7cb2227 , < 66734981b4d3c105223a13c827c9c73be18d91ad (git)
Affected: 8315f42295d2667a7f942f154b73a86fd7cb2227 , < efe8f86c0916f0f74eea74ae21a3b37f728c6bad (git)
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Linux Linux Affected: 3.18
Unaffected: 0 , < 3.18 (semver)
Unaffected: 6.1.188 , ≤ 6.1.* (semver)
Unaffected: 6.6.157 , ≤ 6.6.* (semver)
Unaffected: 6.12.109 , ≤ 6.12.* (semver)
Unaffected: 6.18.50 , ≤ 6.18.* (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm/migrate: report RCU-tasks quiescent states in migrate_pages_batch()\n\nmigrate_pages_batch() unmaps each folio before moving it, and every\nunmap runs the mmu_notifier invalidate callbacks.  On KVM hosts\ntry_to_migrate() ends up in kvm_mmu_notifier_invalidate_range_start() -\u003e\ntdp_mmu_zap_leafs(), which is expensive, so unmapping a large batch keeps\nthe CPU busy for a long time.\n\nThe loop already calls cond_resched(), but on PREEMPTION kernels that is\na no-op, and involuntary preemption is not a Tasks-RCU quiescent state.\n\nA long batch therefore never reports a quiescent state, and the\nmigrating task (e.g. kcompactd) becomes a Tasks-RCU holdout, stalling the\nTasks-RCU grace period for minutes, which is common at Meta fleet:\n\n  INFO: rcu_tasks detected stalls on tasks:\n  0000000055349ecc: .. nvcsw: 1157401/1157401 holdout: 1 idle_cpu: -1/56 task:kcompactd0      state:R  running task\n  Call Trace:\n   tdp_mmu_zap_leafs\n   tdp_mmu_next_root\n   gfn_to_pfn_cache_invalidate_start\n   kvm_mmu_notifier_invalidate_range_start\n   __mmu_notifier_invalidate_range_start\n   try_to_migrate_one\n   try_to_migrate\n   migrate_pages_batch\n   migrate_pages\n   compact_zone\n   compact_node\n   kcompactd\n   kthread\n\nUse cond_resched_tasks_rcu_qs() so a quiescent state is reported even\nwhen cond_resched() does nothing.\n\nThis has also been discussed at [1]"
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    "dateReserved": "2026-09-11T19:38:34.763Z",
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    "redhat_vex": {
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      "current_release_date": "2026-09-15T19:56:02+00:00",
      "cve": "CVE-2026-89756",
      "id": "CVE-2026-89756",
      "initial_release_date": "2026-09-11T00:00:00+00:00",
      "product_status:known_affected": "248",
      "product_status:known_not_affected": "28",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: mm/migrate: report RCU-tasks quiescent states in migrate_pages_batch()",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89756.json",
      "version": "3"
    },
    "suse_vex": {
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      "current_release_date": "2026-09-12T16:22:09Z",
      "cve": "CVE-2026-89756",
      "id": "CVE-2026-89756",
      "initial_release_date": "2026-09-12T16:22:09Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89756",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89756.json",
      "version": "2"
    }
  }
}



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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.