On Mon, Oct 18, 2021 at 03:08:53PM +0800, Youfu Zhang wrote: > Hi, > > I ran into a kernel bug related to blk-throttle on CentOS 7 AltArch for i386. > Userspace programs may panic the kernel if they hit the I/O limit > within 5 minutes after startup. > > Root cause: > 1. jiffies was initialized to -300HZ during boot on 32bit machines > 2. enable blkio cgroup hierarchy > __DEVEL__sane_behavior for cgroup v1 or default hierarchy for cgroup v2 > EL7 kernel modified throtl_pd_init and always enable hierarchical throttling > 3. enable & trigger blkio throttling within 5 minutes after startup > bio propagated from child tg to parent > 4. enter throtl_start_new_slice_with_credit > if(time_after_eq(start, tg->slice_start[rw])) > aka. time_after_eq(0xFFFxxxxx, 0) does not hold > parent tg->slice_start[rw] was zero-initialized and not updated > 5. enter throtl_trim_slice > BUG_ON(time_before(tg->slice_end[rw], tg->slice_start[rw])) > aka. time_before(0xFFFxxxxx, 0) triggers a panic This doesn't reproduce on 5.14. Thanks. -- tejun
