NFS: Add an nfsiod workqueue

NFS post-rpciod cleanups often involve tasks that cannot be safely
performed within the rpciod context (due to deadlock concerns). We
therefore add a dedicated NFS workqueue that can perform tasks like
cleaning up state after an interrupted NFSv4 open() call, or calling
put_nfs_open_context() after an asynchronous read or write call.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index 0f56196..985dc29 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -143,6 +143,7 @@
 extern int nfs_access_cache_shrinker(int nr_to_scan, gfp_t gfp_mask);
 
 /* inode.c */
+extern struct workqueue_struct *nfsiod_workqueue;
 extern struct inode *nfs_alloc_inode(struct super_block *sb);
 extern void nfs_destroy_inode(struct inode *);
 extern int nfs_write_inode(struct inode *,int);