kern/42455: tstile hang with nfs

[Christoph_Egger%gmx.de@localhost]

>Number:         42455
>Category:       kern
>Synopsis:       tstile hang with nfs
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Dec 15 09:40:01 +0000 2009
>Originator:     Christoph Egger
>Release:        NetBSD 5.99.22
>Organization:
>Environment:
NetBSD 5.99.22/Xen amd64
>Description:

The Dom0 has guest images on nfs.
The DomUs do IO on vnd(4). They suddenly freeze while they do IO.

When this happens, commands like 'ls' still work in the Dom0
but comands like 'sync' hang in tstile then and don't give the
shell prompt back.


>How-To-Repeat:

Boot Xen Dom0 and launch a DomU. The guest image for the DomU
must be on nfs.

Do heavy IO in the DomU and wait for the freeze (may take a few
minutes, may also take a few hours).

You notice the freeze when the DomU doesn't react on interrupts
anymore.

Then in the Dom0, commands like 'ls' in the nfs mount works, but
'sync' hangs in tstile.

>Fix: