CVE-2026-98087

What the bug is

A migrate_disable()'d RT task cannot be moved to another CPU, but the scheduler still keeps such a task on that CPU's pushable list (rq->rt.pushable_tasks) and still marks the runqueue RT-overloaded (rq->rt.overloaded = 1). So the RT balancer keeps treating this CPU as having a task to move away, and keeps trying to move the task, but the push can never succeed. When the head is pinned, push_rt_task() does not give up either. It falls back to pushing rq->curr instead, using the per-CPU stopper, as added by commit a7c81556ec4d ("sched: Fix migrate_disable() vs rt/dl balancing"). The CPU spends tens of milliseconds in this retry loop. The core is isolated for real-time work, but during the loop nearly half of its time is consumed by pushes that cannot succeed. An ftrace capture of the affected CPU, with sched_switch enabled and commit 94894c9c477e ("sched/rt: Skip currently executing CPU in rto_next_cpu()") applied, shows where the CPU time went. Two SCHED_FIFO tasks at equal priority shared the CPU, taskA migrate_disable()'d and queued, taskB as rq->curr. In one 89 ms window, taskB got only 52 ms of CPU. The other 37 ms went to the stopper thread. The scheduler kept trying to push taskA, the pinned head of the pushable list, fell back to pushing taskB instead, and woke the stopper 5204 times. Every one of those pushes failed and no task was moved. taskA stayed runnable and queued the whole time, and never ran. Pushing taskB fails on a re-check. find_lock_lowest_rq() drops the rq lock to take the target rq lock, then checks again with "task != pick_next_pushable_task(rq)". The task being pushed is taskB, but the pick returns taskA, the head of the pushable list. taskB is rq->curr, and set_next_task_rt() removes the running task from that list, so taskB can never be the head. The check expects a candidate taken from the pushable list, but the fallback pushes rq->curr, which is never on that list. So the check fails every time. .--> push-IPI arrives | | | v | pushable head = taskA -> pinned, cannot be pushed | | | v | so push taskB instead -> wake migration/N, a stop-class | | thread, so it preempts taskB | v | re-check compares taskB against the pushable head, | which is still taskA -> give up | | | v | nothing moved, taskA still queued, rq still overloaded | | '----------' repeats every ~17 us, 5204 times, for 89 ms The loop cannot stop itself. Every round leaves the runqueue exactly as it was, so the next push-IPI does the same thing. In the capture it ended only when taskB went to sleep on its own. taskA was then picked locally and left the pushable list. CPU time per task in the window, from sched_switch: taskB 51.95 ms real work migration/N 37.18 ms nothing moved taskA 0.00 ms queued the whole time, never picked idle 0.01 ms Counts over the same window: 7667 push-IPIs handled on this CPU 17481 pick_next_pushable_task() returned taskA, still pinned 5204 find_lock_lowest_rq() gave up on the re-check 1 push that actually completed 0 migrations of taskA The CPU times and the window length come from the standard sched_switch tracepoint. The counts needed tracepoints added inside the RT balancer for this investigation. The self-IPI path is closed by the rto_next_cpu() fix above, and that part works. But the runqueue is still marked overloaded, because the pinned task is still advertised as pushable. Other CPUs now send the push-IPIs during their own RT balancing, and the same loop runs again. Closing the self-IPI path did not stop a pinn ---truncated---

Where it lives

The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.

kernel/sched/deadline.c
kernel/sched/rt.c

What this is

SCHEDULERMAINTAINERS section matched on kernel/sched/ · linux-kernel@vger.kernel.org · Maintained

Show whether Debian builds this, per release

Not established. This site could not find the build rule for the affected file in the kernel trees Debian ships, so it has no answer about whether Debian compiles this code. Read that as unknown, never as absent.

• bookworm, trixie, forky, sid?

?

not established - no Makefile entry for the affected file

Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.

From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS

Signals

Published

2026-09-25 (24 days ago)source

CVSS

no vector published, unrated

Attack vector

not published

EPSS

0.17%, higher than 5.5% of all CVEssource

CISA KEV

not listedthe KEV catalogue

Debian urgency

not yet assignedsource

Subsystem

kernel/sched

Upstream fixes

The versions the CNA records as introducing and fixing this, and the commit for each. source

Introduced	Fixed in	Commit
5.11	6.18.53	755476d7ba92
5.11	7.2.7	b0c6f9470577
5.11	7.3	dae5c0292080