[PATCH v8 2/4] blk-throttle: prevent overflow while calculating wait time

Yu Kuai
2022-08-23T03:31:28Z

From: Yu Kuai <yukuai3@huawei.com>

There is a problem found by code review in tg_with_in_bps_limit() that
'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>
---
block/blk-throttle.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index f3c9dcab63e2..773a355d3838 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)
--
2.31.1