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e67e3e738f
Dequeuing a fair task on a throttled hierarchy returns early on encountering a throttled cfs_rq since the throttle path has already dequeued the hierarchy above and has adjusted the h_nr_* accounting till the root cfs_rq. dequeue_entities() crucially misses calling __block_task() for delayed tasks being dequeued on the throttled hierarchies, but this was mostly harmless until commitb7ca5743a2("sched/core: Tweak wait_task_inactive() to force dequeue sched_delayed tasks") since all existing cases would re-enqueue the task if task_on_rq_queued() returned true and the task would eventually be blocked at pick after the hierarchy was unthrottled. wait_task_inactive() is special as it expects the delayed task on throttled hierarchy to reach the blocked state on dequeue but since __block_task() is never called, task_on_rq_queued() continues to return true. Furthermore, since the task is now off the hierarchy, the pick never reaches it to fully block the task even after unthrottle leading to wait_task_inactive() looping endlessly. Remedy this by calling __block_task() if a delayed task is being dequeued on a throttled hierarchy. This fix is only required for stabled kernels implementing delay dequeue (>= v6.12) before v6.18 since upstream commite1fad12dcb("sched/fair: Switch to task based throttle model") indirectly fixes this by removing the early return conditions in dequeue_entities() as part of the per-task throttle feature. Cc: stable@vger.kernel.org Reported-by: Matt Fleming <matt@readmodwrite.com> Closes: https://lore.kernel.org/all/20250925133310.1843863-1-matt@readmodwrite.com/ Fixes:b7ca5743a2("sched/core: Tweak wait_task_inactive() to force dequeue sched_delayed tasks") Tested-by: Matt Fleming <mfleming@cloudflare.com> Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>