sched_ext: Fix this_rq() assumptions in dispatch kfuncs
In the Linux kernel, the following vulnerability has been resolved: sched_ext: Fix this_rq() assumptions in dispatch kfuncs Under core scheduling, dispatch runs from within the core-wide pick and can target a sibling rq, so ops.dispatch() may execute on a CPU different from the dispatched rq's. Several kfunc paths assumed the two always coincide: - scx_dsq_move() decided whether an rq lock is held by testing this_rq()'s rq flags and lock-danced accordingly. A dispatch for a sibling took the unlocked-context branch and acquired the source rq lock on top of the already held dispatched rq lock which could deadlock. - scx_bpf_sub_dispat