Re: [syzbot] [nfs?] INFO: task hung in nfsd_umount

From: Harald Dunkel
Date: Sat Sep 21 2024 - 04:05:52 EST


NeilBrown wrote:

We can guess though. It isn't waiting for a lock - that would show in
the above list - so it might be waiting for a wakeup, or might be
spinning.
The only wake-up I can imagine is in one of the memory-allocation calls,
but if the system were running out of memory we would probably see
messages about that.


I have seen something like this. I am running NFS inside a container,
using legacy cgroup. When it got stuck it claimed I cannot login
into the container due to out of memory. When it happens again, I
can send you the exact error message. The next hung nfsd is overdue,
anyway.

I wonder if it could be looping in svc_xprt_destroy_all(), and sitting
in the msleep() when the hang is detected so there are no locks to
report. I can't see while it would block there.

It would really help to get a full task list.
There is a sysctl for that: /proc/sys/kernel/hung_task_all_cpu_backtrace

Could that be enabled?


I have enabled it on my NFS server (echo 1 >/proc/.../hung_task_all_cpu_backtrace).


Regards

Harri