---
id: "CVE-2026-98463"
kind: "vulnerability"
aliases: ["CVE-2026-98463"]
title: "Linux kernel: sched_ext wakeup flag bug leaves stale reenqueue, crashes scheduler"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["kernel", "linux", "runtime", "sched-ext"]
not_affected_if: []
published_at: "2026-10-18T16:16:56+00:00"
first_seen_at: "2026-10-23T21:57:15+00:00"
updated_at: "2026-10-25T05:27:12+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98463", "first_seen_at": "2026-10-23T21:57:15+00:00"}]
---

# Linux kernel: sched_ext wakeup flag bug leaves stale reenqueue, crashes scheduler

A sched_ext scheduler bug in the Linux kernel leaves a deferred reenqueue request pending after a remote task move. The stale request can point into freed per-cpu memory when the scheduler is disabled, which the next scheduler dereferences.

_Summary, check and fix written by a model from the sources; labelled as such._

## Timeline

- 2026-10-23T21:57:15+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98463

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

sched_ext: Derive SCX_RQ_IN_WAKEUP from the core enqueue flags

schedule_deferred_locked() skips scheduling a deferred action while
SCX_RQ_IN_WAKEUP is set and relies on the task_woken_scx() call that follows
a wakeup enqueue to run it. enqueue_task_scx() sets the flag from the merged
enqueue flags, which include the flags stashed for a remote activation.
move_remote_task_to_local_dsq() thus sets SCX_RQ_IN_WAKEUP on the
destination rq when the moved task was woken up, although no
task_woken_scx() follows that activation.

An IMMED insert into a busy destination requests a local reenqueue during
that enqueue. The request gets linked but not scheduled and stays pending
until an unrelated wakeup or preemption on that CPU runs the deferred
actions. The IMMED task sits behind the running task in the meantime. If
nothing runs them before the scheduler is disabled, the request outlives the
scheduler and points into its freed per-cpu area, which the next scheduler
dereferences from run_deferred().

Test the core enqueue flags for the wakeup bit. Only the core's wakeup path
is followed by task_woken_scx().

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_