Cleaning up vgone.

[Jeff Roberson]

On Thu, 10 Mar 2005, Jeff Roberson wrote:

> I've run into a few vclean races and some related problems with VOP_CLOSE
> not using locks.  I've made some fairly major changes to the way vfs
> handles vnode teardown in the process of fixing this.  I'll summarize what
> I've done here.
>
> The main problem with teardown was the two stage locking scheme involving
> the XLOCK.  I got rid of the XLOCK and simply require the vnode lock
> throughout the whole operation.  To accommodate this, VOP_INACTIVE,
> VOP_RECLAIM, VOP_CLOSE, and VOP_REVOKE all require the vnode lock.  As
> does vgone().
>
> Prior to this, vgone() would set XLOCK and then do a LK_DRAIN to make
> sure there were no callers waiting in VOP_LOCK so that they would always
> see the VI_XLOCK and know that the vnode had changed identities.  Now,
> vgone sets XLOCK, and all lockers who use vget() and vn_lock() check for

This should be "vgone sets VI_DOOMED" which now means "the vnode has been
dissociated from it's filesystem".

> VI_DOOMED before and after acquiring the vnode lock.  To wait for the
> transition to complete, you simply wait on the vnode lock.
>
> This really only required minor changes of the filesystems in the tree.
> Most only required the removal of a VOP_UNLOCK in VOP_INACTIVE, and a few
> acquired the lock in VOP_CLOSE to do operations which they otherwise could
> not.  There is one change to ffs and coda which inspect v_data in their
> vop_lock routines.  This is only safe with the interlock held, where
> before the XLOCK would have protected v_data in the one case that could
> lead to panic.
>
> The patch is available at http://www.chesapeake.net/~jroberson/vgone.diff
>
> Cheers,
> Jeff
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