Re: Vnode API change: VOP_LOCK

[Thomas Klausner <wiz%NetBSD.org@localhost>]

On Fri, Feb 21, 2014 at 12:35:40PM +0100, J. Hannken-Illjes wrote:
> The current implementation of vn_lock() is racy.  Modification of
> the vnode oprations vector for active vnodes is unsafe because it
> is not known whether deadfs or the original file system will be
> called.
> 
> - Pass down LK_RETRY to the lock operation (hint for deadfs only).
> 
> - Split deadfs lock operations from genfs_XXXlock and change
>   deadfs lock operation to return ENOENT if LK_RETRY is unset.
> 
> - Change all other lock operations to check for dead vnode once
>   the vnode is locked and unlock and return ENOENT in this case.
> 
> - Add flag LK_INTERLOCK (requiring LK_NOWAIT) to make it possible
>   for vrelel() to try a lock with v_interlock held.
> 
> With these changes in place vnode lock operations will never succeed
> after vclean() has marked the vnode as VI_XLOCK and before vclean()
> has changed the operations vector.
> 
> Diff available at http://www.netbsd.org/~hannken/vnode-pass3-1.diff
> 
> Comments or objections anyone?

I wanted to understand what you're describing here, but I don't know
what deadfs is, and "apropos deadfs" only pointed to hier(7). Could
someone please describe it, at best in a manpage? (I'm happy to help
with formatting.)
 Thomas