ratelimit: Convert the ->missed field to atomic_t

The ratelimit_state structure's ->missed field is sometimes incremented
locklessly, and it would be good to avoid lost counts.  This is also
needed to count the number of misses due to trylock failure.  Therefore,
convert the ratelimit_state structure's ->missed field to atomic_t.

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

include/linux/ratelimit.h

@@ -24,20 +24,17 @@ static inline void ratelimit_default_init(struct ratelimit_state *rs)
 
 static inline void ratelimit_state_inc_miss(struct ratelimit_state *rs)
 {
-	rs->missed++;
+	atomic_inc(&rs->missed);
 }
 
 static inline int ratelimit_state_get_miss(struct ratelimit_state *rs)
 {
-	return rs->missed;
+	return atomic_read(&rs->missed);
 }
 
 static inline int ratelimit_state_reset_miss(struct ratelimit_state *rs)
 {
-	int ret = rs->missed;
-
-	rs->missed = 0;
-	return ret;
+	return atomic_xchg_relaxed(&rs->missed, 0);
 }
 
 static inline void ratelimit_state_reset_interval(struct ratelimit_state *rs, int interval_init)

include/linux/ratelimit_types.h

@@ -18,7 +18,7 @@ struct ratelimit_state {
 	int		interval;
 	int		burst;
 	int		printed;
-	int		missed;
+	atomic_t	missed;
 	unsigned int	flags;
 	unsigned long	begin;
 };

lib/ratelimit.c

@@ -66,7 +66,7 @@ int ___ratelimit(struct ratelimit_state *rs, const char *func)
 		rs->printed++;
 		ret = 1;
 	} else {
-		rs->missed++;
+		ratelimit_state_inc_miss(rs);
 		ret = 0;
 	}
 	raw_spin_unlock_irqrestore(&rs->lock, flags);