sched_ext: Fix for v6.19-rc8

Hi, Linus.

This is a critical regression fix for a change introduced in this cycle.

The cgroup exit ordering fix (7900aa699c34) which moved sched_ext_free() to finish_task_switch() created a race window where sched_class operations could be invoked on dead tasks after sched_ext_dead() already ran, leading to invalid SCX task state transitions and NULL pointer dereferences.

Thanks.

The following changes since commit c9894e6f0160414b57e895332c580cf5c8da6780:

tools/sched_ext: update scx_show_state.py for scx_aborting change (2025-12-28 06:11:26 -1000)

are available in the Git repository at:

https://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git tags/sched_ext-for-6.19-rc8-fixes

for you to fetch changes up to 0eca95cba2b7bf7b7b4f2fa90734a85fcaa72782:

sched_ext: Short-circuit sched_class operations on dead tasks (2026-02-04 12:22:11 -1000)

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sched_ext: Fixes for v6.19-rc8

- Fix race where sched_class operations (sched_setscheduler() and friends) could be invoked on dead tasks after sched_ext_dead() already ran, causing invalid SCX task state transitions and NULL pointer dereferences. This was a regression from the cgroup exit ordering fix which moved sched_ext_free() to finish_task_switch().

----------------------------------------------------------------
Tejun Heo (1):
sched_ext: Short-circuit sched_class operations on dead tasks

 kernel/sched/ext.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

--
tejun