Recurring problem: processes block accessing UFS file system

[Don Lewis]

On  5 Jan, Denis Shaposhnikov wrote:
>>>>>> "Don" == Don Lewis <truckman at FreeBSD.org> writes:
> 
>  Don> Are you using any unusual file systems, such as nullfs or
>  Don> unionfs?
> 
> Yes, I'm use a lots of nullfs. This is a host system for about 20
> jails with nullfs mounted ro system:

That would be my guess as to the cause of the problem. Hopefully
DEBUG_VFS_LOCKS will help pinpoint the bug.