ratelimit: extend to print suppressed messages on release

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.

Link: http://lkml.kernel.org/r/20160716061745.15795-2-bp@alien8.de
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Dave Young <dyoung@redhat.com>
Cc: Franck Bui <fbui@suse.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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++;