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>

fs/nfs/inode.c

@@ -1219,6 +1219,36 @@ static void nfs_destroy_inodecache(void)
 	kmem_cache_destroy(nfs_inode_cachep);
 }
 
+struct workqueue_struct *nfsiod_workqueue;
+
+/*
+ * start up the nfsiod workqueue
+ */
+static int nfsiod_start(void)
+{
+	struct workqueue_struct *wq;
+	dprintk("RPC:       creating workqueue nfsiod\n");
+	wq = create_singlethread_workqueue("nfsiod");
+	if (wq == NULL)
+		return -ENOMEM;
+	nfsiod_workqueue = wq;
+	return 0;
+}
+
+/*
+ * Destroy the nfsiod workqueue
+ */
+static void nfsiod_stop(void)
+{
+	struct workqueue_struct *wq;
+
+	wq = nfsiod_workqueue;
+	if (wq == NULL)
+		return;
+	nfsiod_workqueue = NULL;
+	destroy_workqueue(wq);
+}
+
 /*
  * Initialize NFS
  */
@@ -1226,6 +1256,10 @@ static int __init init_nfs_fs(void)
 {
 	int err;
 
+	err = nfsiod_start();
+	if (err)
+		goto out6;
+
 	err = nfs_fs_proc_init();
 	if (err)
 		goto out5;
@@ -1272,6 +1306,8 @@ static int __init init_nfs_fs(void)
 out4:
 	nfs_fs_proc_exit();
 out5:
+	nfsiod_stop();
+out6:
 	return err;
 }
 
@@ -1287,6 +1323,7 @@ static void __exit exit_nfs_fs(void)
 #endif
 	unregister_nfs_fs();
 	nfs_fs_proc_exit();
+	nfsiod_stop();
 }
 
 /* Not quite true; I just maintain it */

fs/nfs/internal.h

@@ -143,6 +143,7 @@ extern struct rpc_procinfo nfs4_procedures[];
 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);