1a:
- scheduler() acquires p->lock
- checks if p->state == RUNNABLE
- sets p->state = RUNNING
- sets c->proc = p
- calls swtch()

1b:
- process acquires p->lock (in yield(), sleep(), or kexit())
- changes p->state to RUNNABLE, SLEEPING, or ZOMBIE
- calls sched() -> swtch() to switch back to scheduler thread
- scheduler() sets c->proc = 0
- scheduler() releases p->lock so process can be picked up again

2:
No, it scans proc[] linearly from start to end