FKIE_CVE-2026-74686

Vulnerability from fkie_nvd - Published: 2026-08-22 16:16 - Updated: 2026-08-22 16:16
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: rqspinlock: Reset tail when preserving queue on deadlock Currently, the destruction of the waiter queue is suppressed for rqspinlock in cases where a deadlock is detected. Deadlock checks happen relatively frequently (on entry for AA, within 1ms for ABBA), and waiter threads may not be involved in locking scenarios involving deadlocks. Thus, it is useful to not flush the queue and let other waiters take a stab at acquiring the lock after we detect a deadlock and exit. However, we need to follow the same logic as what we did previously for the waitq_timeout label: reset the tail, and if we cannot, signal the next waiter appropriately. In case of deadlocks, this signal would just mark the MCS node as unlocked, and in case of timeouts, it would signal RES_TIMEOUT_VAL. The difference thus is in the value propagated, which decides whether the queue remains active or gets flushed. Not doing the tail reset, and waiting for the next waiter can lead to cases where we are the final waiter, and thus no next waiter arrives, leading to intermittent stalls in this path. Once the next waiter does join, we will be unblocked. In the theoretical case when the next waiter never joins, we risk stalling indefinitely. This can only happen for ABBA deadlocks, since entry into the wait queue is guarded with AA checks. A precise sequence of executions leading up to this scenario can be: CPU 0 holds lock A. CPU 1 holds lock B. CPU 2 attempts lock B, becomes the pending waiter for B. CPU 0 attempts lock B. B has locked+pending bits set, thus CPU 0 queues. CPU 1 attempts lock A. CPU 0 detects an ABBA deadlock. Once deadlock detection happens for CPU 0, it will sit waiting for the next waiter in the queue to populate node->next, which will experience delays until such a waiter arrives. Fix this by adjusting the logic for the check for deadlocks preceding the waitq_timeout label. It would make sense to consolidate code for both cases and use 'ret' to distinguish the value being propagated, but that is left as an exercise for a future refactoring task to avoid diff noise in this patch.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/7a3c0289c3c8eb4607dff448ae9ff9f902c813af
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/f54667b0c16213285c9d9b8e3929f738b8f71826
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "kernel/bpf/rqspinlock.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "f54667b0c16213285c9d9b8e3929f738b8f71826",
              "status": "affected",
              "version": "7bd6e5ce5be666fb3fb873bf20f77e62555b7835",
              "versionType": "git"
            },
            {
              "lessThan": "7a3c0289c3c8eb4607dff448ae9ff9f902c813af",
              "status": "affected",
              "version": "7bd6e5ce5be666fb3fb873bf20f77e62555b7835",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "kernel/bpf/rqspinlock.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.19"
            },
            {
              "lessThan": "6.19",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.9",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nrqspinlock: Reset tail when preserving queue on deadlock\n\nCurrently, the destruction of the waiter queue is suppressed for\nrqspinlock in cases where a deadlock is detected. Deadlock checks happen\nrelatively frequently (on entry for AA, within 1ms for ABBA), and waiter\nthreads may not be involved in locking scenarios involving deadlocks.\nThus, it is useful to not flush the queue and let other waiters take a\nstab at acquiring the lock after we detect a deadlock and exit.\n\nHowever, we need to follow the same logic as what we did previously for\nthe waitq_timeout label: reset the tail, and if we cannot, signal the\nnext waiter appropriately. In case of deadlocks, this signal would just\nmark the MCS node as unlocked, and in case of timeouts, it would signal\nRES_TIMEOUT_VAL. The difference thus is in the value propagated, which\ndecides whether the queue remains active or gets flushed.\n\nNot doing the tail reset, and waiting for the next waiter can lead to\ncases where we are the final waiter, and thus no next waiter arrives,\nleading to intermittent stalls in this path. Once the next waiter does\njoin, we will be unblocked. In the theoretical case when the next waiter\nnever joins, we risk stalling indefinitely.\n\nThis can only happen for ABBA deadlocks, since entry into the wait queue\nis guarded with AA checks. A precise sequence of executions leading up\nto this scenario can be:\n\nCPU 0 holds lock A.\nCPU 1 holds lock B.\nCPU 2 attempts lock B, becomes the pending waiter for B.\nCPU 0 attempts lock B. B has locked+pending bits set, thus CPU 0 queues.\nCPU 1 attempts lock A.\nCPU 0 detects an ABBA deadlock.\n\nOnce deadlock detection happens for CPU 0, it will sit waiting for the\nnext waiter in the queue to populate node-\u003enext, which will experience\ndelays until such a waiter arrives.\n\nFix this by adjusting the logic for the check for deadlocks preceding\nthe waitq_timeout label. It would make sense to consolidate code for\nboth cases and use \u0027ret\u0027 to distinguish the value being propagated, but\nthat is left as an exercise for a future refactoring task to avoid diff\nnoise in this patch."
    }
  ],
  "id": "CVE-2026-74686",
  "lastModified": "2026-08-22T16:16:42.973",
  "metrics": {},
  "published": "2026-08-22T16:16:42.973",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/7a3c0289c3c8eb4607dff448ae9ff9f902c813af"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/f54667b0c16213285c9d9b8e3929f738b8f71826"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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