Re: kern/43439 (mount_null panic: lockdebug_wantlock: locking against myself)

[hannken%NetBSD.org@localhost]

Synopsis: mount_null panic: lockdebug_wantlock: locking against myself

Responsible-Changed-From-To: kern-bug-people->hannken
Responsible-Changed-By: hannken%NetBSD.org@localhost
Responsible-Changed-When: Wed, 09 Jun 2010 09:02:06 +0000
Responsible-Changed-Why:
Broke it and have to handle it.


State-Changed-From-To: open->analyzed
State-Changed-By: hannken%NetBSD.org@localhost
State-Changed-When: Wed, 09 Jun 2010 09:02:06 +0000
State-Changed-Why:
- do_sys_mount makes the mounted-on vnode lock recursive.  This is a
  layered vnode.
- nullfs_mount looks up the lower vnode, traverses the leaf of the
  mounted-on vnode.
- while the mounted-on vnode has recursive locking, its leaf has not
  => locking against self

Two possible solutions:
1) Remove recursive vnode locks and move mount-on lookup into the file systems
2) Add a bypass function to layered file systems to pass vn_setrecurse down