sched_ext: Skip sub-disable teardown for never-linked sub-schedulers

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A sub-scheduler enable can fail before scx_link_sched() links the sched into
the hierarchy, e.g. when the parent is already being disabled, and cleanup
still runs the full scx_sub_disable().

That is racy against root disable: drain_descendants() is the only ordering
between a sub's disable-time task walk and root disable's all-task teardown,
and an unlinked sub is invisible to it. Root's teardown can thus run between
the never-linked sub's drain and its walk, exiting every task to no
scheduler.

The walk then trips the membership WARN and re-homes the exited tasks onto
the dying hierarchy, a use-after-free.

Skip the cgroup ownership reset and the task walk if @sch was never linked,
indicated by the empty ->sibling as unlinking only happens later in the same
function. The membership WARN remains valid: a linked sub is always waited
on by an ancestor's drain.

Fixes: 337ec00b1d ("sched_ext: Implement cgroup sub-sched enabling and disabling")
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

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Tejun Heo 2026-07-16 10:45:23 -10:00

parent 5f8b69642d

commit 8c13364db9

1 changed files with 12 additions and 2 deletions

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kernel/sched/ext/ext.c

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