NFSv4: keep state manager thread active if swap is enabled

If we are swapping over NFSv4, we may not be able to allocate memory to
start the state-manager thread at the time when we need it.
So keep it always running when swap is enabled, and just signal it to
start.

This requires updating and testing the cl_swapper count on the root
rpc_clnt after following all ->cl_parent links.
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/file.c

@@ -483,8 +483,9 @@ static int nfs_swap_activate(struct swap_info_struct *sis, struct file *file,
 {
 	unsigned long blocks;
 	long long isize;
-	struct rpc_clnt *clnt = NFS_CLIENT(file->f_mapping->host);
-	struct inode *inode = file->f_mapping->host;
+	struct inode *inode = file_inode(file);
+	struct rpc_clnt *clnt = NFS_CLIENT(inode);
+	struct nfs_client *cl = NFS_SERVER(inode)->nfs_client;
 
 	spin_lock(&inode->i_lock);
 	blocks = inode->i_blocks;
@@ -497,14 +498,22 @@ static int nfs_swap_activate(struct swap_info_struct *sis, struct file *file,
 
 	*span = sis->pages;
 
+
+	if (cl->rpc_ops->enable_swap)
+		cl->rpc_ops->enable_swap(inode);
+
 	return rpc_clnt_swap_activate(clnt);
 }
 
 static void nfs_swap_deactivate(struct file *file)
 {
-	struct rpc_clnt *clnt = NFS_CLIENT(file->f_mapping->host);
+	struct inode *inode = file_inode(file);
+	struct rpc_clnt *clnt = NFS_CLIENT(inode);
+	struct nfs_client *cl = NFS_SERVER(inode)->nfs_client;
 
 	rpc_clnt_swap_deactivate(clnt);
+	if (cl->rpc_ops->disable_swap)
+		cl->rpc_ops->disable_swap(file_inode(file));
 }
 
 const struct address_space_operations nfs_file_aops = {

fs/nfs/nfs4_fs.h

@@ -42,6 +42,7 @@ enum nfs4_client_state {
 	NFS4CLNT_LEASE_MOVED,
 	NFS4CLNT_DELEGATION_EXPIRED,
 	NFS4CLNT_RUN_MANAGER,
+	NFS4CLNT_MANAGER_AVAILABLE,
 	NFS4CLNT_RECALL_RUNNING,
 	NFS4CLNT_RECALL_ANY_LAYOUT_READ,
 	NFS4CLNT_RECALL_ANY_LAYOUT_RW,

fs/nfs/nfs4proc.c

@@ -10468,6 +10468,24 @@ static ssize_t nfs4_listxattr(struct dentry *dentry, char *list, size_t size)
 	return error + error2 + error3;
 }
 
+static void nfs4_enable_swap(struct inode *inode)
+{
+	/* The state manager thread must always be running.
+	 * It will notice the client is a swapper, and stay put.
+	 */
+	struct nfs_client *clp = NFS_SERVER(inode)->nfs_client;
+
+	nfs4_schedule_state_manager(clp);
+}
+
+static void nfs4_disable_swap(struct inode *inode)
+{
+	/* The state manager thread will now exit once it is
+	 * woken.
+	 */
+	wake_up_var(&NFS_SERVER(inode)->nfs_client->cl_state);
+}
+
 static const struct inode_operations nfs4_dir_inode_operations = {
 	.create		= nfs_create,
 	.lookup		= nfs_lookup,
@@ -10545,6 +10563,8 @@ const struct nfs_rpc_ops nfs_v4_clientops = {
 	.create_server	= nfs4_create_server,
 	.clone_server	= nfs_clone_server,
 	.discover_trunking = nfs4_discover_trunking,
+	.enable_swap	= nfs4_enable_swap,
+	.disable_swap	= nfs4_disable_swap,
 };
 
 static const struct xattr_handler nfs4_xattr_nfs4_acl_handler = {

fs/nfs/nfs4state.c

@@ -1207,10 +1207,17 @@ void nfs4_schedule_state_manager(struct nfs_client *clp)
 {
 	struct task_struct *task;
 	char buf[INET6_ADDRSTRLEN + sizeof("-manager") + 1];
+	struct rpc_clnt *cl = clp->cl_rpcclient;
+
+	while (cl != cl->cl_parent)
+		cl = cl->cl_parent;
 
 	set_bit(NFS4CLNT_RUN_MANAGER, &clp->cl_state);
-	if (test_and_set_bit(NFS4CLNT_MANAGER_RUNNING, &clp->cl_state) != 0)
+	if (test_and_set_bit(NFS4CLNT_MANAGER_AVAILABLE, &clp->cl_state) != 0) {
+		wake_up_var(&clp->cl_state);
 		return;
+	}
+	set_bit(NFS4CLNT_MANAGER_RUNNING, &clp->cl_state);
 	__module_get(THIS_MODULE);
 	refcount_inc(&clp->cl_count);
 
@@ -1226,6 +1233,7 @@ void nfs4_schedule_state_manager(struct nfs_client *clp)
 		printk(KERN_ERR "%s: kthread_run: %ld\n",
 			__func__, PTR_ERR(task));
 		nfs4_clear_state_manager_bit(clp);
+		clear_bit(NFS4CLNT_MANAGER_AVAILABLE, &clp->cl_state);
 		nfs_put_client(clp);
 		module_put(THIS_MODULE);
 	}
@@ -2680,12 +2688,8 @@ static void nfs4_state_manager(struct nfs_client *clp)
 			clear_bit(NFS4CLNT_RECALL_RUNNING, &clp->cl_state);
 		}
 
-		/* Did we race with an attempt to give us more work? */
-		if (!test_bit(NFS4CLNT_RUN_MANAGER, &clp->cl_state))
-			return;
-		if (test_and_set_bit(NFS4CLNT_MANAGER_RUNNING, &clp->cl_state) != 0)
 		return;
-		memflags = memalloc_nofs_save();
+
 	} while (refcount_read(&clp->cl_count) > 1 && !signalled());
 	goto out_drain;
 
@@ -2706,9 +2710,31 @@ static void nfs4_state_manager(struct nfs_client *clp)
 static int nfs4_run_state_manager(void *ptr)
 {
 	struct nfs_client *clp = ptr;
+	struct rpc_clnt *cl = clp->cl_rpcclient;
+
+	while (cl != cl->cl_parent)
+		cl = cl->cl_parent;
 
 	allow_signal(SIGKILL);
+again:
+	set_bit(NFS4CLNT_MANAGER_RUNNING, &clp->cl_state);
 	nfs4_state_manager(clp);
+	if (atomic_read(&cl->cl_swapper)) {
+		wait_var_event_interruptible(&clp->cl_state,
+					     test_bit(NFS4CLNT_RUN_MANAGER,
+						      &clp->cl_state));
+		if (atomic_read(&cl->cl_swapper) &&
+		    test_bit(NFS4CLNT_RUN_MANAGER, &clp->cl_state))
+			goto again;
+		/* Either no longer a swapper, or were signalled */
+	}
+	clear_bit(NFS4CLNT_MANAGER_AVAILABLE, &clp->cl_state);
+
+	if (refcount_read(&clp->cl_count) > 1 && !signalled() &&
+	    test_bit(NFS4CLNT_RUN_MANAGER, &clp->cl_state) &&
+	    !test_and_set_bit(NFS4CLNT_MANAGER_AVAILABLE, &clp->cl_state))
+		goto again;
+
 	nfs_put_client(clp);
 	module_put_and_kthread_exit(0);
 	return 0;

include/linux/nfs_xdr.h

@@ -1797,6 +1797,8 @@ struct nfs_rpc_ops {
 	struct nfs_server *(*clone_server)(struct nfs_server *, struct nfs_fh *,
 					   struct nfs_fattr *, rpc_authflavor_t);
 	int	(*discover_trunking)(struct nfs_server *, struct nfs_fh *);
+	void	(*enable_swap)(struct inode *inode);
+	void	(*disable_swap)(struct inode *inode);
 };
 
 /*

net/sunrpc/clnt.c

@@ -3069,6 +3069,8 @@ rpc_clnt_swap_activate_callback(struct rpc_clnt *clnt,
 int
 rpc_clnt_swap_activate(struct rpc_clnt *clnt)
 {
+	while (clnt != clnt->cl_parent)
+		clnt = clnt->cl_parent;
 	if (atomic_inc_return(&clnt->cl_swapper) == 1)
 		return rpc_clnt_iterate_for_each_xprt(clnt,
 				rpc_clnt_swap_activate_callback, NULL);