Linux Kernel: Scheduler Race Fixes Head Into Release Candidate
Late-cycle fixes converged on sched_ext's handling of state that goes stale during transitions - idle tracking, hotplug, and error timing - alongside a cgroup use-after-free and two sysctl range-check regressions.
Duration: PT2M42S
Episode overview
This episode is a short developer briefing from Linux Kernel.
It explains recent repository work in plain language.
- Show: Linux Kernel
- Published: 2026-09-16T13:17:52Z
- Audio duration: PT2M42S
Transcript excerpt
This excerpt keeps the crawler page concise. Listen to the episode or use the RSS feed for the full update.
This is Linux Kernel for September 16th, 2026.
The dominant story today is timing bugs in scheduler state - the moment where the kernel's view of a CPU or task falls out of sync with reality.
Tejun Heo's sched_ext pull, merged by Linus in 9b87fdc, is the clearest example. Several fixes deal with stale state windows. One closed a gap where an error raised before a scheduler finished enabling could get swallowed by the disable path, leaving a broken scheduler running until it was freed while still in use -…
Commit a9e3760 adds a new online CID mask, maintained by the kernel inside the scheduler's arena. Schedulers that install their own CPU ID mapping previously had no reliable way to know which IDs were online after a hotplug event - the old count-based check didn't work for them. This mask is kept live and updated…
The example scheduler, scx_qmap, got its own round of related fixes. Commit 9a0b159 addresses a case where a CPU claims an idle ID, gets kicked to run a task, but the task doesn't arrive - say, after an affinity change bounces it to the global queue. Without this fix, that CPU's ID stayed marked busy indefinitely.…
Second theme: two smaller but sharp regressions. Cgroup's…
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