diff mbox series

[RESEND,v6,2/8] blk-throttle: prevent overflow while calculating wait time

Message ID 20220701093441.885741-3-yukuai1@huaweicloud.com (mailing list archive)
State New, archived
Headers show
Series bugfix and cleanup for blk-throttle | expand

Commit Message

Yu Kuai July 1, 2022, 9:34 a.m. UTC 
From: Yu Kuai <yukuai3@huawei.com>

In tg_with_in_bps_limit(), 'bps_limit * jiffy_elapsed_rnd' might
overflow. FIx the problem by calling mul_u64_u64_div_u64() instead.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/blk-throttle.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

Comments

Tejun Heo July 27, 2022, 6:28 p.m. UTC | #1 
On Fri, Jul 01, 2022 at 05:34:35PM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
> 
> In tg_with_in_bps_limit(), 'bps_limit * jiffy_elapsed_rnd' might
> overflow. FIx the problem by calling mul_u64_u64_div_u64() instead.
> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>

Acked-by: Tejun Heo <tj@kernel.org>

BTW, have you observed this happening or is it from just reviewing the code?

Thanks.
Yu Kuai July 28, 2022, 10:23 a.m. UTC | #2 
在 2022/07/28 2:28, Tejun Heo 写道:
> On Fri, Jul 01, 2022 at 05:34:35PM +0800, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> In tg_with_in_bps_limit(), 'bps_limit * jiffy_elapsed_rnd' might
>> overflow. FIx the problem by calling mul_u64_u64_div_u64() instead.
>>
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> 
> Acked-by: Tejun Heo <tj@kernel.org>
> 
> BTW, have you observed this happening or is it from just reviewing the code?

It's just from code review.

Thanks.
> 
> Thanks.
>
diff mbox series

Patch

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 5c1d1c4d8188..a89c62bef2fb 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -806,7 +806,7 @@  static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
 				 u64 bps_limit, unsigned long *wait)
 {
 	bool rw = bio_data_dir(bio);
-	u64 bytes_allowed, extra_bytes, tmp;
+	u64 bytes_allowed, extra_bytes;
 	unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
 	unsigned int bio_size = throtl_bio_data_size(bio);
 
@@ -824,10 +824,8 @@  static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
 		jiffy_elapsed_rnd = tg->td->throtl_slice;
 
 	jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, tg->td->throtl_slice);
-
-	tmp = bps_limit * jiffy_elapsed_rnd;
-	do_div(tmp, HZ);
-	bytes_allowed = tmp;
+	bytes_allowed = mul_u64_u64_div_u64(bps_limit, (u64)jiffy_elapsed_rnd,
+					    (u64)HZ);
 
 	if (tg->bytes_disp[rw] + bio_size <= bytes_allowed) {
 		if (wait)