ratelimit: Force re-initialization when rate-limiting re-enabled

Currently, if rate limiting is disabled, ___ratelimit() does an immediate
early return with no state changes.  This can result in false-positive
drops when re-enabling rate limiting.  Therefore, mark the ratelimit_state
structure "uninitialized" when rate limiting is disabled.

[ paulmck: Apply Petr Mladek feedback. ]

Link: https://lore.kernel.org/all/fbe93a52-365e-47fe-93a4-44a44547d601@paulmck-laptop/
Link: https://lore.kernel.org/all/20250423115409.3425-1-spasswolf@web.de/
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Kuniyuki Iwashima <kuniyu@amazon.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>

Author: paulmckrcu

lib/ratelimit.c

@@ -35,11 +35,24 @@ int ___ratelimit(struct ratelimit_state *rs, const char *func)
 	unsigned long flags;
 	int ret;
 
+	/*
+	 * Zero interval says never limit, otherwise, non-positive burst
+	 * says always limit.
+	 */
 	if (interval <= 0 || burst <= 0) {
 		ret = interval == 0 || burst > 0;
+		if (!(READ_ONCE(rs->flags) & RATELIMIT_INITIALIZED) || (!interval && !burst) ||
+		    !raw_spin_trylock_irqsave(&rs->lock, flags)) {
+			if (!ret)
+				ratelimit_state_inc_miss(rs);
+			return ret;
+		}
+
+		/* Force re-initialization once re-enabled. */
+		rs->flags &= ~RATELIMIT_INITIALIZED;
 		if (!ret)
 			ratelimit_state_inc_miss(rs);
-		return ret;
+		goto unlock_ret;
 	}
 
 	/*