sched_ext: Generalize the reject DSQ reenqueue path

The reject DSQ is currently specific to sub-scheduler cap failures. Its
storage and initialization depend on CONFIG_EXT_SUB_SCHED, and the drain
path assumes every rejected task was rejected for SCX_TASK_REENQ_CAP.

Other transient placement failures need the same ability to park a task
on its source rq and return it to the owning BPF scheduler. Make the
reject DSQ unconditional and carry the reenqueue reason directly in
p->scx.flags from the rejection site.

A reenqueue reason remains valid while ops.enqueue() runs so that BPF
can inspect it. Clear it immediately after the callback returns and
before resolving a direct dispatch. Paths which bypass ops.enqueue()
clear the reason before the kernel-selected placement. A rejection from
the new placement can therefore install its reason into a clear field.
Route all paths through a common cleanup point to enforce this ordering.

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