{"id":"CVE-2026-89756","title":"mm/migrate: report RCU-tasks quiescent states in migrate_pages_batch()","summary":"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 …","severity":"medium","cvss":5.5,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","cvssSource":"vendor","cwe":["CWE-821"],"vendor":"Linux","product":"Linux","affected":["Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < 8c6d63d434ebb85c6cf3dac1e70a171b183c6614","Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < 4757542649af56d894e25e30f57cd497dffad53f","Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < 4996a7bc01ef35570664854dac2530c604981039","Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < 5dc0daff0341c6baba19c38f47d299ac831d7e99","Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < 66734981b4d3c105223a13c827c9c73be18d91ad","Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < efe8f86c0916f0f74eea74ae21a3b37f728c6bad","Linux 3.18"],"published":"2026-09-11","updated":"2026-10-19","sourceUpdated":"2026-10-19T08:52:09.900Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-89756","references":[{"url":"https://git.kernel.org/stable/c/8c6d63d434ebb85c6cf3dac1e70a171b183c6614"},{"url":"https://git.kernel.org/stable/c/4757542649af56d894e25e30f57cd497dffad53f"},{"url":"https://git.kernel.org/stable/c/4996a7bc01ef35570664854dac2530c604981039"},{"url":"https://git.kernel.org/stable/c/5dc0daff0341c6baba19c38f47d299ac831d7e99"},{"url":"https://git.kernel.org/stable/c/66734981b4d3c105223a13c827c9c73be18d91ad"},{"url":"https://git.kernel.org/stable/c/efe8f86c0916f0f74eea74ae21a3b37f728c6bad"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89756.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-89756"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2532146"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-89756"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89756"},{"url":"https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89756.mbox"}],"tags":["cve.org","csaf","vex","red-hat"],"epss":0.00197,"epssPercentile":0.09325,"ingestedAt":"2026-09-14T15:23:07.448Z","slug":"CVE-2026-89756","body":"## Overview\n\nIn 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() ->\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]\n\n## Affected\n\n- `Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < 8c6d63d434ebb85c6cf3dac1e70a171b183c6614`\n- `Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < 4757542649af56d894e25e30f57cd497dffad53f`\n- `Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < 4996a7bc01ef35570664854dac2530c604981039`\n- `Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < 5dc0daff0341c6baba19c38f47d299ac831d7e99`\n- `Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < 66734981b4d3c105223a13c827c9c73be18d91ad`\n- `Linux >= 8315f42295d2667a7f942f154b73a86fd7cb2227 < efe8f86c0916f0f74eea74ae21a3b37f728c6bad`\n- `Linux 3.18`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, … · updated 2026-09-15 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89756.json)","depth":"sunlit","depthScore":30,"depthScoreParts":{"impact":30.3,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[{"seq":205522,"id":"CVE-2026-89756","ts":1789576723233,"field":"cvss","old":"4.7","new":"5.5"},{"seq":204079,"id":"CVE-2026-89756","ts":1789490231348,"field":"cvss","old":null,"new":"4.7"},{"seq":204078,"id":"CVE-2026-89756","ts":1789490231348,"field":"severity","old":"none","new":"medium"},{"seq":147674,"id":"CVE-2026-89756","ts":1789270211834,"field":"cvss","old":null,"new":"4.7"},{"seq":147673,"id":"CVE-2026-89756","ts":1789270211834,"field":"severity","old":"none","new":"medium"},{"seq":109422,"id":"CVE-2026-89756","ts":1789183731852,"field":"cvss","old":null,"new":"4.7"},{"seq":109421,"id":"CVE-2026-89756","ts":1789183731852,"field":"severity","old":"none","new":"medium"}]}