PUFFS deadlock

[manu%netbsd.org@localhost (Emmanuel Dreyfus)]

Emmanuel Dreyfus <manu%netbsd.org@localhost> wrote:

> What about adding a timeout in struct puffs_msgpark and use it for
> inactive operations? Returning EAGAIN from puffs_vnop_inactive seems an
> easy way to work around this deadlock.

I reply to myself. This will probably break many things since
VOP_INACTIVE return code is not checked, neither in vrelel() nor in
vclean(). 

As I understand, the problem will occur when:

1) a PUFFS filesystem does a namei(), most likely on a path component
leading to its filesystem mont point. It sleeps for the parent vnode
lock.

2) another process which locks the desired vnode goes the
getnewvnode/getcleanvnode/vclean/VOP_INACTIVE
path on a vnode in the PUFFS filesystem.

3) PUFFS is sleeping in kernel and will never service the VOP_INACTIVE.
The vnode remains locked forever. Since it is very likely to be the root
vnode, all processes doing a VOP_LOOKUP end up sleeping for the root
vnode lock.
 
How can this be fixed?

-- 
Emmanuel Dreyfus
http://hcpnet.free.fr/pubz
manu%netbsd.org@localhost