Re: [PATCH v2 2/2] nfsd: avoid taking the state_lock while holding the i_lock

[Christoph Hellwig <hch@infradead.org>]

On Fri, Jun 06, 2014 at 09:07:06AM -0400, Jeff Layton wrote:
> state_lock is a heavily contended global lock. We don't want to grab
> that while simultaneously holding the inode->i_lock. Avoid doing that in
> the delegation break callback by ensuring that we add/remove the
> dl_perfile under a new per-nfs4_file fi_lock, and hold that while walking
> the fi_delegations list.
> 
> We still do need to queue the delegations to the global del_recall_lru
> list. Do that in the rpc_prepare op for the delegation recall RPC. It's
> possible though that the allocation of the rpc_task will fail, which
> would cause the delegation to be leaked.
> 
> If that occurs rpc_release is still called, so we also do it there if
> the rpc_task failed to run. This brings up another dilemma -- how do
> we know whether it got queued in rpc_prepare or not?
> 
> In order to determine that, we set the dl_time to 0 in the delegation
> break callback from the VFS and only set it when we queue it to the
> list. If it's still zero by the time we get to rpc_release, then we know
> that it never got queued and we can do it then.

Compared to this version I have to say the original one that I objected
to looks like the lesser evil.  I'll take another deeper look at it.