[PATCH v3 2/4] xen/console: correct leaky-bucket rate limiter

[dmukhin@xxxxxxxx]

From: Denis Mukhin <dmukhin@xxxxxxxx> 

Use existing printk_ratelimit_ms and printk_ratelimit_burst variables in
do_printk_ratelimit() instead of hardcoded values 5000 and 10 respectively.

Ensure rate limiter is disabled if either printk_ratelimit_ms or
printk_ratelimit_burst is 0. Make sure no unnecessary initialization is done
in the corner case.

Also, simplify the limiter code by using min().

Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
---
Changes since v2:
- fixed typing and 32-bit integer overflow problem
---
 xen/drivers/char/console.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 5d395f882e08..de9f2432445d 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -1274,21 +1274,26 @@ bool __printk_ratelimit(unsigned int ratelimit_ms,
                         unsigned int ratelimit_burst)
 {
     static DEFINE_SPINLOCK(ratelimit_lock);
-    static unsigned long toks = 10 * 5 * 1000;
-    static unsigned long last_msg;
+    static unsigned long long toks, last_msg;
     static unsigned int missed;
+    unsigned long long now, limit;
     unsigned long flags;
-    unsigned long long now = NOW(); /* ns */
-    unsigned long ms;
+    s_time_t ms;
 
-    do_div(now, 1000000);
-    ms = (unsigned long)now;
+    if ( !ratelimit_burst || !ratelimit_burst )
+        return true;
+
+    limit = min(ratelimit_burst * ratelimit_ms, UINT_MAX);
+    if ( !toks )
+        toks = limit;
+
+    now = NOW(); /* ns */
+    ms = do_div(now, MILLISECS(1));
 
     spin_lock_irqsave(&ratelimit_lock, flags);
     toks += ms - last_msg;
     last_msg = ms;
-    if ( toks > (ratelimit_burst * ratelimit_ms))
-        toks = ratelimit_burst * ratelimit_ms;
+    toks = min(toks, limit);
     if ( toks >= ratelimit_ms )
     {
         unsigned int lost = missed;
-- 
2.54.0