[PATCH AUTOSEL 6.1 08/21] blk-iocost: fix divide by 0 error in calc_lcoefs()

Sasha Levin
2023-02-26T03:45:19Z

From: Li Nan <linan122@huawei.com>

[ Upstream commit 984af1e66b4126cf145153661cc24c213e2ec231 ]

echo max of u64 to cost.model can cause divide by 0 error.

# echo 8:0 rbps=18446744073709551615 > /sys/fs/cgroup/io.cost.model

divide error: 0000 [#1] PREEMPT SMP
RIP: 0010:calc_lcoefs+0x4c/0xc0
Call Trace:
<TASK>
ioc_refresh_params+0x2b3/0x4f0
ioc_cost_model_write+0x3cb/0x4c0
? _copy_from_iter+0x6d/0x6c0
? kernfs_fop_write_iter+0xfc/0x270
cgroup_file_write+0xa0/0x200
kernfs_fop_write_iter+0x17d/0x270
vfs_write+0x414/0x620
ksys_write+0x73/0x160
__x64_sys_write+0x1e/0x30
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

calc_lcoefs() uses the input value of cost.model in DIV_ROUND_UP_ULL,
overflow would happen if bps plus IOC_PAGE_SIZE is greater than
ULLONG_MAX, it can cause divide by 0 error.

Fix the problem by setting basecost

Signed-off-by: Li Nan <linan122@huawei.com>
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20230117070806.3857142-5-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/blk-iocost.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 495396425bade..bfc33fa9a063c 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -865,9 +865,14 @@ static void calc_lcoefs(u64 bps, u64 seqiops, u64 randiops,

*page = *seqio = *randio = 0;

- if (bps)
- *page = DIV64_U64_ROUND_UP(VTIME_PER_SEC,
- DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE));
+ if (bps) {
+ u64 bps_pages = DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE);
+
+ if (bps_pages)
+ *page = DIV64_U64_ROUND_UP(VTIME_PER_SEC, bps_pages);
+ else
+ *page = 1;
+ }

if (seqiops) {
v = DIV64_U64_ROUND_UP(VTIME_PER_SEC, seqiops);
--
2.39.0