In fact, we did encounter such a special situation where the kernel printed out `iocg: invalid donation weights in /a/b/c: active=1 donating=1 after=0`, and then it immediately panic. I analyzed the code but could not figure out how this happened; it might be a concurrency issue or some other hidden bug. Our kernel is not the latest, but it includes the patch edaa26334c117a584add6053f48d63a988d25a6e (iocost: Fix divide-by-zero on donation from low hweight cgroup). 在 2024/11/22 16:16，“Yu Kuai”<yukuai1@xxxxxxxxxxxxxxx <mailto:yukuai1@xxxxxxxxxxxxxxx>> 写入: Hi, 在 2024/11/22 15:26, Kunhai Dai 写道: > The hweight_inuse calculation in transfer_surpluses() could potentially > result in a value of 0, which would lead to division by zero errors in > subsequent calculations that use this value as a divisor. > > Signed-off-by: Kunhai Dai <daikunhai@xxxxxxxxxxxxxx <mailto:daikunhai@xxxxxxxxxxxxxx>> > --- > block/blk-iocost.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/block/blk-iocost.c b/block/blk-iocost.c > index 384aa15e8260..65cdb55d30cc 100644 > --- a/block/blk-iocost.c > +++ b/block/blk-iocost.c > @@ -1999,9 +1999,10 @@ static void transfer_surpluses(struct list_head *surpluses, struct ioc_now *now) > parent = iocg->ancestors[iocg->level - 1]; > > /* b' = gamma * b_f + b_t' */ > - iocg->hweight_inuse = DIV64_U64_ROUND_UP( > - (u64)gamma * (iocg->hweight_active - iocg->hweight_donating), > - WEIGHT_ONE) + iocg->hweight_after_donation; > + iocg->hweight_inuse = max_t(u64, 1, > + DIV64_U64_ROUND_UP( > + (u64)gamma * (iocg->hweight_active - iocg->hweight_donating), > + WEIGHT_ONE) + iocg->hweight_after_donation); I'm confused, how could DIV64_U64_Round_UP() end up less than 1? #define DIV64_U64_ROUND_UP(ll, d) \ ({ u64 _tmp = (d); div64_u64((ll) + _tmp - 1, _tmp); }) AFAIK, the only case that could happen is that iocg->hweight_active - iocg->hweight_donating is 0, then I don't get it now how cound active iocg donate all the hweight, if this really happend perhaps the better solution is to avoid such case. Thanks, Kuai > > /* w' = s' * b' / b'_p */ > inuse = DIV64_U64_ROUND_UP( >
