linux-kernel - [PATCH RFC 5/9] ratelimit: Convert the ->missed field to atomic

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Message-Id: <20250403211514.985900-5-paulmck@kernel.org>
Date: Thu,  3 Apr 2025 14:15:10 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: kernel-team@...a.com,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kuniyuki Iwashima <kuniyu@...zon.com>,
	Mateusz Guzik <mjguzik@...il.com>,
	Petr Mladek <pmladek@...e.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: [PATCH RFC 5/9] 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 try-lock failure.  Therefore,
convert the rratelimit_state structure's ->missed field to atomic_t.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: Mateusz Guzik <mjguzik@...il.com>
Cc: Petr Mladek <pmladek@...e.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: John Ogness <john.ogness@...utronix.de>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>
---
 include/linux/ratelimit.h       | 9 +++------
 include/linux/ratelimit_types.h | 2 +-
 lib/ratelimit.c                 | 2 +-
 3 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/include/linux/ratelimit.h b/include/linux/ratelimit.h
index 8400c5356c187..c78b92b3e5cd8 100644
--- a/include/linux/ratelimit.h
+++ b/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)
diff --git a/include/linux/ratelimit_types.h b/include/linux/ratelimit_types.h
index 765232ce0b5e9..d21fe82b67f67 100644
--- a/include/linux/ratelimit_types.h
+++ b/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;
 };
diff --git a/lib/ratelimit.c b/lib/ratelimit.c
index 85e22f00180c5..18703f92d73e7 100644
--- a/lib/ratelimit.c
+++ b/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);
-- 
2.40.1