Revert "net: Remove conditional threaded-NAPI wakeup based on task state."

This reverts commit 03765d5 which is
commit 56364c9 upstream.

It is only for issues around PREEMPT_RT, which is not in the 6.6.y tree,
so revert this for now.

Link: https://lore.kernel.org/r/20260120103833.4kssDD1Y@linutronix.de
Reported-by: Jakub Kicinski <kuba@kernel.org>
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Wen Yang <wen.yang@linux.dev>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: gregkh

net/core/dev.c

@@ -4539,7 +4539,13 @@ static inline void ____napi_schedule(struct softnet_data *sd,
 		 */
 		thread = READ_ONCE(napi->thread);
 		if (thread) {
-			set_bit(NAPI_STATE_SCHED_THREADED, &napi->state);
+			/* Avoid doing set_bit() if the thread is in
+			 * INTERRUPTIBLE state, cause napi_thread_wait()
+			 * makes sure to proceed with napi polling
+			 * if the thread is explicitly woken from here.
+			 */
+			if (READ_ONCE(thread->__state) != TASK_INTERRUPTIBLE)
+				set_bit(NAPI_STATE_SCHED_THREADED, &napi->state);
 			wake_up_process(thread);
 			return;
 		}
@@ -6695,6 +6701,8 @@ static int napi_poll(struct napi_struct *n, struct list_head *repoll)
 
 static int napi_thread_wait(struct napi_struct *napi)
 {
+	bool woken = false;
+
 	set_current_state(TASK_INTERRUPTIBLE);
 
 	while (!kthread_should_stop()) {
@@ -6703,13 +6711,15 @@ static int napi_thread_wait(struct napi_struct *napi)
 		 * Testing SCHED bit is not enough because SCHED bit might be
 		 * set by some other busy poll thread or by napi_disable().
 		 */
-		if (test_bit(NAPI_STATE_SCHED_THREADED, &napi->state)) {
+		if (test_bit(NAPI_STATE_SCHED_THREADED, &napi->state) || woken) {
 			WARN_ON(!list_empty(&napi->poll_list));
 			__set_current_state(TASK_RUNNING);
 			return 0;
 		}
 
 		schedule();
+		/* woken being true indicates this thread owns this napi. */
+		woken = true;
 		set_current_state(TASK_INTERRUPTIBLE);
 	}
 	__set_current_state(TASK_RUNNING);