ratelimit: Avoid jiffies=0 special case

The ___ratelimit() function special-cases the jiffies-counter value of zero
as "uninitialized".  This works well on 64-bit systems, where the jiffies
counter is not going to return to zero for more than half a billion years
on systems with HZ=1000, but similar 32-bit systems take less than 50 days
to wrap the jiffies counter.  And although the consequences of wrapping the
jiffies counter seem to be limited to minor confusion on the duration of
the rate-limiting interval that happens to end at time zero, it is almost
no work to avoid this confusion.

Therefore, introduce a RATELIMIT_INITIALIZED bit to the ratelimit_state
structure's ->flags field so that a ->begin value of zero is no longer
special.

Link: https://lore.kernel.org/all/fbe93a52-365e-47fe-93a4-44a44547d601@paulmck-laptop/
Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Paul E. McKenney <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Kuniyuki Iwashima <[email protected]>
Cc: Mateusz Guzik <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: John Ogness <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>

Author: paulmckrcu

include/linux/ratelimit.h

@@ -43,7 +43,7 @@ static inline void ratelimit_state_reset_interval(struct ratelimit_state *rs, in
 
 	raw_spin_lock_irqsave(&rs->lock, flags);
 	rs->interval = interval_init;
-	rs->begin = 0;
+	rs->flags &= ~RATELIMIT_INITIALIZED;
 	rs->printed = 0;
 	ratelimit_state_reset_miss(rs);
 	raw_spin_unlock_irqrestore(&rs->lock, flags);

include/linux/ratelimit_types.h

@@ -11,6 +11,7 @@
 
 /* issue num suppressed message on exit */
 #define RATELIMIT_MSG_ON_RELEASE	BIT(0)
+#define RATELIMIT_INITIALIZED		BIT(1)
 
 struct ratelimit_state {
 	raw_spinlock_t	lock;		/* protect the state */

lib/ratelimit.c

@@ -49,8 +49,10 @@ int ___ratelimit(struct ratelimit_state *rs, const char *func)
 		return 0;
 	}
 
-	if (!rs->begin)
+	if (!(rs->flags & RATELIMIT_INITIALIZED)) {
 		rs->begin = jiffies;
+		rs->flags |= RATELIMIT_INITIALIZED;
+	}
 
 	if (time_is_before_jiffies(rs->begin + interval)) {
 		int m = ratelimit_state_reset_miss(rs);