sched_ext: Fix rq->core_pick corruption under core scheduling

{
  "id": "eac500685365ae2429d744450075cab29103041a8a770dac7bf440e12034dd43",
  "url": "https://osv.dev/vulnerability/CVE-2026-89517",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "sched_ext: Fix rq->core_pick corruption under core scheduling",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: sched_ext: Fix rq->core_pick corruption under core scheduling Core scheduling's pick_next_task() picks what to run on every SMT sibling of the core in a single pass under the shared core-wide rq lock. The selection state is consistent only while the lock is held continuously, so ->pick_task() originally could not release it. However, since 4c95380701f5 (\"sched/ext: Fold balance_scx() into pick_task_scx()\"), sched_ext runs dispatch from inside the pick and dispatching can drop the rq lock. To support this, pick_next_task() has been updated to restart the whole selection when a pick returns RETRY_TASK after releasing the lock. When selections on the same core interleave through the dropped lock, they corrupt each other's state: one clears the other's rq->core_pick leading to a NULL deref, or invalidates its keep-the-previous-task decision leaving a dequeued task running, which deadlocks the next wakeup and matches the reported hard hangs. A cookied ping-pong load on an SMT machine makes the interleavings frequent and kills the kernel within seconds. Fix it by making the pick return RETRY_TASK whenever dispatch released the rq lock, so that a selection only ever commits picks made under a continuously held lock. The previous patch's rq->scx.lock_drop_seq counts the releases. A dispatch that touched nothing never releases the lock and its verdict, including \"nothing to run\", stands: retries are bounded, each foll",
    "evidence": "osv:CVE-2026-89517",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "7.2.4",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-89517",
      "aliases": [
        "CVE-2026-89517"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                  "introduced": "4c95380701f58b8112f0b891de8d160e4199e19d"
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                {
                  "fixed": "cdafb68155bee2d5c4e50c12e4606323e9334e6b"
                },
                {
                  "fixed": "d954004205c1a1d3f59ce8482b559266c15600fa"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89517.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.2.4"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89517.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:25.855266588Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/cdafb68155bee2d5c4e50c12e4606323e9334e6b",
        "https://git.kernel.org/stable/c/d954004205c1a1d3f59ce8482b559266c15600fa",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89517.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-89517",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89517.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-89517",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 492554,
  "published_at": "2026-09-11T19:44:00.576+00:00"
}