linux-kernel - [PATCH] ratelimit: fix bug in time interval by resetting right begin time

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Date:	Wed, 20 Jan 2016 23:36:53 +0900
From:	Jaewon Kim <jaewon31.kim@...il.com>
To:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Cc:	Jaewon Kim <jaewon31.kim@...il.com>
Subject: [PATCH] ratelimit: fix bug in time interval by resetting right begin time

rs->begin in ratelimit is set in two cases.
1) when rs->begin was not initialized
2) when rs->interval was passed
For the case 2), current ratelimit sets the begin to 0. This incurrs improper
suppression. The begin value will be set in the next ratelimit call by 1).
Then the time interval check will be always false, and rs->printed will not be
initialized. Although enough time passed, ratelimit may return 0 if rs->printed
is not less than rs->burst. To reset interval properly, begin should be jiffies
rather than 0.

For an example code below,
	static DEFINE_RATELIMIT_STATE(mylimit, 1, 1);
	for (i = 1; i <= 10; i++) {
		if (__ratelimit(&mylimit))
			printk("ratelimit test count %d\n", i);
		msleep(3000);
	}
test result in the current code shows suppression even there is 3 seconds sleep.
[  78.391148] ratelimit test count 1
[  81.295988] ratelimit test count 2
[  87.315981] ratelimit test count 4
[  93.336267] ratelimit test count 6
[  99.356031] ratelimit test count 8
[ 105.376367] ratelimit test count 10

Signed-off-by: Jaewon Kim <jaewon31.kim@...il.com>
---
 lib/ratelimit.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/ratelimit.c b/lib/ratelimit.c
index 40e03ea..2c5de86 100644
--- a/lib/ratelimit.c
+++ b/lib/ratelimit.c
@@ -49,7 +49,7 @@ int ___ratelimit(struct ratelimit_state *rs, const char *func)
 		if (rs->missed)
 			printk(KERN_WARNING "%s: %d callbacks suppressed\n",
 				func, rs->missed);
-		rs->begin   = 0;
+		rs->begin   = jiffies;
 		rs->printed = 0;
 		rs->missed  = 0;
 	}
-- 
1.9.1