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CVE-2026-89517 (GCVE-0-2026-89517)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:44 – Updated: 2026-09-11 19:44
VLAI
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 following a dispatch that actually did something, and an idle CPU does not loop. If another dispatch is already in flight on the rq, skip dispatching and pick from what is already queued locally - the in-flight dispatch has released the lock, so its own selection will retry and re-pick this rq, while returning RETRY_TASK here would only spin on the lock that dispatch needs to finish. Balance callbacks must run in the context that queued them, so they can only be queued on the CPU's own rq. When dispatching for another rq, run the deferred work directly instead - that rq may consume all its picks through the core-sched fast path and never queue the callback itself. The put_prev_task_scx() warning about a runnable task being left behind assumed that dispatch ran as part of the very pick that is switching away. That now only holds on the non-core path, so gate it and drop the cookie-match test, which is always true without core scheduling, from its condition.
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 4c95380701f58b8112f0b891de8d160e4199e19d , < cdafb68155bee2d5c4e50c12e4606323e9334e6b (git)
Affected: 4c95380701f58b8112f0b891de8d160e4199e19d , < d954004205c1a1d3f59ce8482b559266c15600fa (git)
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Linux Linux Affected: 6.19
Unaffected: 0 , < 6.19 (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\nsched_ext: Fix rq-\u003ecore_pick corruption under core scheduling\n\nCore scheduling\u0027s pick_next_task() picks what to run on every SMT sibling of\nthe core in a single pass under the shared core-wide rq lock. The selection\nstate is consistent only while the lock is held continuously, so\n-\u003epick_task() originally could not release it. However, since 4c95380701f5\n(\"sched/ext: Fold balance_scx() into pick_task_scx()\"), sched_ext runs\ndispatch from inside the pick and dispatching can drop the rq lock. To\nsupport this, pick_next_task() has been updated to restart the whole\nselection when a pick returns RETRY_TASK after releasing the lock.\n\nWhen selections on the same core interleave through the dropped lock, they\ncorrupt each other\u0027s state: one clears the other\u0027s rq-\u003ecore_pick leading to\na NULL deref, or invalidates its keep-the-previous-task decision leaving a\ndequeued task running, which deadlocks the next wakeup and matches the\nreported hard hangs. A cookied ping-pong load on an SMT machine makes the\ninterleavings frequent and kills the kernel within seconds.\n\nFix it by making the pick return RETRY_TASK whenever dispatch released the\nrq lock, so that a selection only ever commits picks made under a\ncontinuously held lock. The previous patch\u0027s rq-\u003escx.lock_drop_seq counts\nthe releases. A dispatch that touched nothing never releases the lock and\nits verdict, including \"nothing to run\", stands: retries are bounded, each\nfollowing a dispatch that actually did something, and an idle CPU does not\nloop.\n\nIf another dispatch is already in flight on the rq, skip dispatching and\npick from what is already queued locally - the in-flight dispatch has\nreleased the lock, so its own selection will retry and re-pick this rq,\nwhile returning RETRY_TASK here would only spin on the lock that dispatch\nneeds to finish.\n\nBalance callbacks must run in the context that queued them, so they can only\nbe queued on the CPU\u0027s own rq. When dispatching for another rq, run the\ndeferred work directly instead - that rq may consume all its picks through\nthe core-sched fast path and never queue the callback itself.\n\nThe put_prev_task_scx() warning about a runnable task being left behind\nassumed that dispatch ran as part of the very pick that is switching away.\nThat now only holds on the non-core path, so gate it and drop the\ncookie-match test, which is always true without core scheduling, from its\ncondition."
        }
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        "shortName": "Linux"
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      "references": [
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          "url": "https://git.kernel.org/stable/c/cdafb68155bee2d5c4e50c12e4606323e9334e6b"
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        {
          "url": "https://git.kernel.org/stable/c/d954004205c1a1d3f59ce8482b559266c15600fa"
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    "cveId": "CVE-2026-89517",
    "datePublished": "2026-09-11T19:44:00.576Z",
    "dateReserved": "2026-09-11T19:38:34.717Z",
    "dateUpdated": "2026-09-11T19:44:00.576Z",
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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-09-15T04:55:56+00:00",
      "cve": "CVE-2026-89517",
      "id": "CVE-2026-89517",
      "initial_release_date": "2026-09-11T19:44:00.576000+00:00",
      "product_status:known_affected": "2",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: Linux kernel: `sched_ext` core scheduling flaw leads to Denial of Service",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89517.json",
      "version": "3"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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