Hello, Baolin. On Tue, Jan 26, 2021 at 09:33:25PM +0800, Baolin Wang wrote: > On !PREEMPT kernel, we can get below softlockup when doing stress > testing with creating and destroying block cgroup repeatly. The > reason is it may take a long time to acquire the queue's lock in > the loop of blkcg_destroy_blkgs(), thus we can use cond_resched() > instead of cpu_relax() to avoid this issue, since the > blkcg_destroy_blkgs() is not called from atomic contexts. > > [ 4757.010308] watchdog: BUG: soft lockup - CPU#11 stuck for 94s! > [ 4757.010698] Call trace: > [ 4757.010700] blkcg_destroy_blkgs+0x68/0x150 > [ 4757.010701] cgwb_release_workfn+0x104/0x158 > [ 4757.010702] process_one_work+0x1bc/0x3f0 > [ 4757.010704] worker_thread+0x164/0x468 > [ 4757.010705] kthread+0x108/0x138 > > Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> * Can you please add might_sleep() at the top of the function? * Given that the system can accumulate a huge number of blkgs in pathological cases, I wonder whether a better way to go about it is explicitly testing need_resched() on each loop and release locks and do cond_resched() if true? Thanks. -- tejun
