sched: Remove pointless preemption disable in sched_submit_work()

Neither wq_worker_sleeping() nor io_wq_worker_sleeping() require to be invoked
with preemption disabled:

  - The worker flag checks operations only need to be serialized against
    the worker thread itself.

  - The accounting and worker pool operations are serialized with locks.

which means that disabling preemption has neither a reason nor a
value. Remove it and update the stale comment.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Link: https://lkml.kernel.org/r/8735pnafj7.ffs@tglx

kernel/sched/core.c

@@ -6251,20 +6251,14 @@ static inline void sched_submit_work(struct task_struct *tsk)
 
 	task_flags = tsk->flags;
 	/*
-	 * If a worker went to sleep, notify and ask workqueue whether
-	 * it wants to wake up a task to maintain concurrency.
-	 * As this function is called inside the schedule() context,
-	 * we disable preemption to avoid it calling schedule() again
-	 * in the possible wakeup of a kworker and because wq_worker_sleeping()
-	 * requires it.
+	 * If a worker goes to sleep, notify and ask workqueue whether it
+	 * wants to wake up a task to maintain concurrency.
 	 */
 	if (task_flags & (PF_WQ_WORKER | PF_IO_WORKER)) {
-		preempt_disable();
 		if (task_flags & PF_WQ_WORKER)
 			wq_worker_sleeping(tsk);
 		else
 			io_wq_worker_sleeping(tsk);
-		preempt_enable_no_resched();
 	}
 
 	if (tsk_is_pi_blocked(tsk))