Description
In the Linux kernel, the following vulnerability has been resolved:
sched_ext: Fix rq->core_pick corruption under core scheduling
Core scheduling's pick_next_task() picks what to run on every SMT sibling of
the core in a single pass under the shared core-wide rq lock. The selection
state is consistent only while the lock is held continuously, so
->pick_task() originally could not release it. However, since 4c95380701f5
("sched/ext: Fold balance_scx() into pick_task_scx()"), sched_ext runs
dispatch from inside the pick and dispatching can drop the rq lock. To
support this, pick_next_task() has been updated to restart the whole
selection when a pick returns RETRY_TASK after releasing the lock.
When selections on the same core interleave through the dropped lock, they
corrupt each other's state: one clears the other's rq->core_pick leading to
a NULL deref, or invalidates its keep-the-previous-task decision leaving a
dequeued task running, which deadlocks the next wakeup and matches the
reported hard hangs. A cookied ping-pong load on an SMT machine makes the
interleavings frequent and kills the kernel within seconds.
Fix it by making the pick return RETRY_TASK whenever dispatch released the
rq lock, so that a selection only ever commits picks made under a
continuously held lock. The previous patch's rq->scx.lock_drop_seq counts
the releases. A dispatch that touched nothing never releases the lock and
its verdict, including "nothing to run", stands: retries are bounded, each
following a dispatch that actually did something, and an idle CPU does not
loop.
If another dispatch is already in flight on the rq, skip dispatching and
pick from what is already queued locally - the in-flight dispatch has
released the lock, so its own selection will retry and re-pick this rq,
while returning RETRY_TASK here would only spin on the lock that dispatch
needs to finish.
Balance callbacks must run in the context that queued them, so they can only
be queued on the CPU's own rq. When dispatching for another rq, run the
deferred work directly instead - that rq may consume all its picks through
the core-sched fast path and never queue the callback itself.
The put_prev_task_scx() warning about a runnable task being left behind
assumed that dispatch ran as part of the very pick that is switching away.
That now only holds on the non-core path, so gate it and drop the
cookie-match test, which is always true without core scheduling, from its
condition.
sched_ext: Fix rq->core_pick corruption under core scheduling
Core scheduling's pick_next_task() picks what to run on every SMT sibling of
the core in a single pass under the shared core-wide rq lock. The selection
state is consistent only while the lock is held continuously, so
->pick_task() originally could not release it. However, since 4c95380701f5
("sched/ext: Fold balance_scx() into pick_task_scx()"), sched_ext runs
dispatch from inside the pick and dispatching can drop the rq lock. To
support this, pick_next_task() has been updated to restart the whole
selection when a pick returns RETRY_TASK after releasing the lock.
When selections on the same core interleave through the dropped lock, they
corrupt each other's state: one clears the other's rq->core_pick leading to
a NULL deref, or invalidates its keep-the-previous-task decision leaving a
dequeued task running, which deadlocks the next wakeup and matches the
reported hard hangs. A cookied ping-pong load on an SMT machine makes the
interleavings frequent and kills the kernel within seconds.
Fix it by making the pick return RETRY_TASK whenever dispatch released the
rq lock, so that a selection only ever commits picks made under a
continuously held lock. The previous patch's rq->scx.lock_drop_seq counts
the releases. A dispatch that touched nothing never releases the lock and
its verdict, including "nothing to run", stands: retries are bounded, each
following a dispatch that actually did something, and an idle CPU does not
loop.
If another dispatch is already in flight on the rq, skip dispatching and
pick from what is already queued locally - the in-flight dispatch has
released the lock, so its own selection will retry and re-pick this rq,
while returning RETRY_TASK here would only spin on the lock that dispatch
needs to finish.
Balance callbacks must run in the context that queued them, so they can only
be queued on the CPU's own rq. When dispatching for another rq, run the
deferred work directly instead - that rq may consume all its picks through
the core-sched fast path and never queue the callback itself.
The put_prev_task_scx() warning about a runnable task being left behind
assumed that dispatch ran as part of the very pick that is switching away.
That now only holds on the non-core path, so gate it and drop the
cookie-match test, which is always true without core scheduling, from its
condition.
Analysis
Analysis and contextual insights are available on OpenCVE Cloud.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
|||||||||||||||
| Linux | Linux | affected |
|
No data.
No data.
No data available yet.
Remediation
No vendor fix or workaround currently provided.
Additional remediation guidance may be available on OpenCVE Cloud.
Tracking
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Advisories
No advisories yet.
References
History
Sat, 12 Sep 2026 00:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Weaknesses | CWE-476 | |
| References |
| |
| Metrics |
threat_severity
|
cvssV3_1
|
Fri, 11 Sep 2026 23:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: sched_ext: Fix rq->core_pick corruption under core scheduling Core scheduling's pick_next_task() picks what to run on every SMT sibling of the core in a single pass under the shared core-wide rq lock. The selection state is consistent only while the lock is held continuously, so ->pick_task() originally could not release it. However, since 4c95380701f5 ("sched/ext: Fold balance_scx() into pick_task_scx()"), sched_ext runs dispatch from inside the pick and dispatching can drop the rq lock. To support this, pick_next_task() has been updated to restart the whole selection when a pick returns RETRY_TASK after releasing the lock. When selections on the same core interleave through the dropped lock, they corrupt each other's state: one clears the other's rq->core_pick leading to a NULL deref, or invalidates its keep-the-previous-task decision leaving a dequeued task running, which deadlocks the next wakeup and matches the reported hard hangs. A cookied ping-pong load on an SMT machine makes the interleavings frequent and kills the kernel within seconds. Fix it by making the pick return RETRY_TASK whenever dispatch released the rq lock, so that a selection only ever commits picks made under a continuously held lock. The previous patch's rq->scx.lock_drop_seq counts the releases. A dispatch that touched nothing never releases the lock and its verdict, including "nothing to run", stands: retries are bounded, each following a dispatch that actually did something, and an idle CPU does not loop. If another dispatch is already in flight on the rq, skip dispatching and pick from what is already queued locally - the in-flight dispatch has released the lock, so its own selection will retry and re-pick this rq, while returning RETRY_TASK here would only spin on the lock that dispatch needs to finish. Balance callbacks must run in the context that queued them, so they can only be queued on the CPU's own rq. When dispatching for another rq, run the deferred work directly instead - that rq may consume all its picks through the core-sched fast path and never queue the callback itself. The put_prev_task_scx() warning about a runnable task being left behind assumed that dispatch ran as part of the very pick that is switching away. That now only holds on the non-core path, so gate it and drop the cookie-match test, which is always true without core scheduling, from its condition. | |
| Title | sched_ext: Fix rq->core_pick corruption under core scheduling | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-09-11T19:44:00.576Z
Reserved: 2026-09-11T19:38:34.717Z
Link: CVE-2026-89517
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-09-11T20:19:34.287
Modified: 2026-09-11T20:19:34.287
Link: CVE-2026-89517
Redhat
OpenCVE Enrichment
No data.
Weaknesses
-
CWE-476
NULL Pointer Dereference