NFS: Fix a hang in the writeback path

Now that the inode scalability patches have been merged, it is no longer
safe to call igrab() under the inode->i_lock.
Now that we no longer call nfs_clear_request() until the nfs_page is
being freed, we know that we are always holding a reference to the
nfs_open_context, which again holds a reference to the path, and so
the inode cannot be freed until the last nfs_page has been removed
from the radix tree and freed.

We can therefore skip the igrab()/iput() altogether.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/pagelist.c

@@ -135,14 +135,14 @@ void nfs_clear_page_tag_locked(struct nfs_page *req)
 		nfs_unlock_request(req);
 }
 
-/**
+/*
  * nfs_clear_request - Free up all resources allocated to the request
  * @req:
  *
  * Release page and open context resources associated with a read/write
  * request after it has completed.
  */
-void nfs_clear_request(struct nfs_page *req)
+static void nfs_clear_request(struct nfs_page *req)
 {
 	struct page *page = req->wb_page;
 	struct nfs_open_context *ctx = req->wb_context;