Hi, 在 2023/01/05 5:54, Tejun Heo 写道:
On Mon, Dec 26, 2022 at 04:58:58PM +0800, Yu Kuai wrote:From: Li Nan <linan122@xxxxxxxxxx> 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@xxxxxxxxxx> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx> --- block/blk-iocost.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/block/blk-iocost.c b/block/blk-iocost.c index f8726e20da20..c6b39024117b 100644 --- a/block/blk-iocost.c +++ b/block/blk-iocost.c @@ -866,9 +866,13 @@ 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) { + if (bps >= U64_MAX - IOC_PAGE_SIZE) + *page = 1; + else + *page = DIV64_U64_ROUND_UP(VTIME_PER_SEC, + DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE)); + }This is a nitpick but wouldn't something like the following be easier to understand? if (bps) { u64 bps_pages = DIV_ROUND_UP_ULL(bps, IOC_PAGE_SIZE); if (bps_pages) *pages = DIV64_U64_ROUND_UP(VTIME_PER_SEC, bps_pages); else *pages = 1; }
Yes, I agree that this is better to understand. I'll send a new version. Thanks, Kuai
