| Message ID | 20221226085859.2701195-5-yukuai1@huaweicloud.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | blk-iocost: random bugfix | expand |
On Mon, Dec 26, 2022 at 04:58:58PM +0800, Yu Kuai wrote: > From: Li Nan <linan122@huawei.com> > > 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> > --- > 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; } Out of scope but this seems more like a bug in the DIV macros. The fact that it returns 0 is an implementation artifact more than anything and a surprising one at that as it ends up returning 0 for an input that a regular division would handle just fine and the rounded up result fits well within the result type. Thanks.
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@huawei.com> >> >> 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> >> --- >> 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
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)); + } if (seqiops) { v = DIV64_U64_ROUND_UP(VTIME_PER_SEC, seqiops);