[PATCH -v5 1/2] ratelimit: Extend to print suppressed messages on release

[Borislav Petkov]

From: Borislav Petkov <bp@xxxxxxx>

Extend the ratelimiting facility to print the amount of suppressed lines
when it is being released.

This use case is aimed at short-termed, burst-like users for which we
want to output the suppressed lines stats only once, after it has been
disposed of. For an example, see /dev/kmsg usage in a follow-on patch.

Also, change the printk() line we issue on release to not use "callbacks"
as it is misleading: we're not suppressing callbacks but printk() calls.

This has been separated from a previous patch by Linus.

Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: Franck Bui <fbui@xxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Uwe Kleine-KÃnig <u.kleine-koenig@xxxxxxxxxxxxxx>
---
 include/linux/ratelimit.h | 38 +++++++++++++++++++++++++++++++++-----
 lib/ratelimit.c           | 10 ++++++----
 2 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/include/linux/ratelimit.h b/include/linux/ratelimit.h
index 18102529254e..57c9e0622a38 100644
--- a/include/linux/ratelimit.h
+++ b/include/linux/ratelimit.h
@@ -2,11 +2,15 @@
 #define _LINUX_RATELIMIT_H
 
 #include <linux/param.h>
+#include <linux/sched.h>
 #include <linux/spinlock.h>
 
 #define DEFAULT_RATELIMIT_INTERVAL	(5 * HZ)
 #define DEFAULT_RATELIMIT_BURST		10
 
+/* issue num suppressed message on exit */
+#define RATELIMIT_MSG_ON_RELEASE	BIT(0)
+
 struct ratelimit_state {
 	raw_spinlock_t	lock;		/* protect the state */
 
@@ -15,6 +19,7 @@ struct ratelimit_state {
 	int		printed;
 	int		missed;
 	unsigned long	begin;
+	unsigned long	flags;
 };
 
 #define RATELIMIT_STATE_INIT(name, interval_init, burst_init) {		\
@@ -34,12 +39,35 @@ struct ratelimit_state {
 static inline void ratelimit_state_init(struct ratelimit_state *rs,
 					int interval, int burst)
 {
+	memset(rs, 0, sizeof(*rs));
+
 	raw_spin_lock_init(&rs->lock);
-	rs->interval = interval;
-	rs->burst = burst;
-	rs->printed = 0;
-	rs->missed = 0;
-	rs->begin = 0;
+	rs->interval	= interval;
+	rs->burst	= burst;
+}
+
+static inline void ratelimit_default_init(struct ratelimit_state *rs)
+{
+	return ratelimit_state_init(rs, DEFAULT_RATELIMIT_INTERVAL,
+					DEFAULT_RATELIMIT_BURST);
+}
+
+static inline void ratelimit_state_exit(struct ratelimit_state *rs)
+{
+	if (!(rs->flags & RATELIMIT_MSG_ON_RELEASE))
+		return;
+
+	if (rs->missed) {
+		pr_warn("%s: %d output lines suppressed due to ratelimiting\n",
+			current->comm, rs->missed);
+		rs->missed = 0;
+	}
+}
+
+static inline void
+ratelimit_set_flags(struct ratelimit_state *rs, unsigned long flags)
+{
+	rs->flags = flags;
 }
 
 extern struct ratelimit_state printk_ratelimit_state;
diff --git a/lib/ratelimit.c b/lib/ratelimit.c
index 2c5de86460c5..08f8043cac61 100644
--- a/lib/ratelimit.c
+++ b/lib/ratelimit.c
@@ -46,12 +46,14 @@ int ___ratelimit(struct ratelimit_state *rs, const char *func)
 		rs->begin = jiffies;
 
 	if (time_is_before_jiffies(rs->begin + rs->interval)) {
-		if (rs->missed)
-			printk(KERN_WARNING "%s: %d callbacks suppressed\n",
-				func, rs->missed);
+		if (rs->missed) {
+			if (!(rs->flags & RATELIMIT_MSG_ON_RELEASE)) {
+				pr_warn("%s: %d callbacks suppressed\n", func, rs->missed);
+				rs->missed = 0;
+			}
+		}
 		rs->begin   = jiffies;
 		rs->printed = 0;
-		rs->missed  = 0;
 	}
 	if (rs->burst && rs->burst > rs->printed) {
 		rs->printed++;
-- 
2.8.4