sched_ext: Clear a sub-scheduler's caps before ops.sub_detach()

A sub-scheduler can leave standing state behind on the cids delegated to it,
cpuperf targets being the obvious case, and the kernel does not track who
wrote it. Restoring it is the parent's job and ops.sub_detach() is the place
for it. Today the parent can't rely on that: the dying sub-scheduler keeps
every cap until it is marked dead after ops.exit(), so its ops.exit() or a
late timer can write after the parent has cleaned up.

Clear every cap of the sub-scheduler before ops.sub_detach(). The pshard
caps go first as a pending sync recomputes ecaps from them, and ecaps are
then zeroed directly. A grant racing the clear is refused under the child's
pshard lock, so nothing hands the caps back.

Fixes: 86094b95efcf ("sched_ext: Add per-shard cap delegation for sub-schedulers")
Signed-off-by: Tejun Heo <tj@kernel.org>

0 files changed, 0 insertions, 0 deletions