Hi
在 2024/11/24 21:44, 戴坤海 Tony Dai 写道:
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.
Do you have a reporducer for this? I'd like to take a look at the
WARN first.
Thanks,
Kuai
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(
