sched_ext: Block proxy donors before taking control

Proxy execution retains mutex-blocked donors on the runqueue so their
scheduling context can execute a lock owner. sched_ext cannot safely
inherit such donors unless the BPF scheduler explicitly participates in
their admission and ordering.

Make sched_ext reject retained donors by default. Implement
scx_allow_proxy_exec() to force blocked EXT tasks through the regular
block path in schedule().

A donor retained by another scheduling class may already be queued when
sched_ext is enabled or when a task switches to SCHED_EXT. Fully block
the donor before sched_change_begin() records its queued state. This
prevents sched_ext from importing a proxy session which the BPF
scheduler did not admit, while leaving ordinary FAIR, RT and DL class
transitions untouched.

This is a preparatory change to support proxy execution with sched_ext.

Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

0 files changed, 0 insertions, 0 deletions