On Tue 08-10-19 09:06:29, Qian Cai wrote: > On Tue, 2019-10-08 at 14:39 +0200, Michal Hocko wrote: > > On Tue 08-10-19 08:00:43, Qian Cai wrote: > > > > > > > > > > On Oct 8, 2019, at 6:39 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > > > > > Have you actually triggered any real deadlock? With a zone->lock in > > > > place it would be pretty clear with hard lockups detected. > > > > > > Yes, I did trigger here and there, and those lockdep splats are > > > especially useful to figure out why. > > > > Can you provide a lockdep splat from an actual deadlock please? I am > > sorry but your responses tend to be really cryptic and I never know when > > you are talking about actual deadlocks and lockdep splats. I have asked > > about the former several times never receiving a specific answer. > > It is very time-consuming to confirm a lockdep splat is 100% matching a deadlock > giving that it is not able to reproduce on will yet, so when I did encounter a > memory offline deadlock where "echo offline > memory/state" just hang, but there > is no hard lockup probably because the hard lockup detector did not work > properly for some reasons or it keep trying to acquire a spin lock that only > keep the CPU 100%. If there is a real deadlock due to zone->lock then you would certainly get a hard lockup splat. So I strongly suspect that you are seeing a completely different problem. Most likely some pages cannot be migrated and the offlining code will retry for ever. You can terminate that from the userspace by a fatal signal of course. -- Michal Hocko SUSE Labs
