NFSv4.1: Add a helper pnfs_commit_and_return_layout

In order to be able to safely return the layout in nfs4_proc_setattr,
we need to block new uses of the layout, wait for all outstanding
users of the layout to complete, commit the layout and then return it.

This patch adds a helper in order to do all this safely.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Cc: Boaz Harrosh <bharrosh@panasas.com>

fs/nfs/nfs4proc.c

@@ -2632,7 +2632,7 @@ nfs4_proc_setattr(struct dentry *dentry, struct nfs_fattr *fattr,
 	int status;
 
 	if (pnfs_ld_layoutret_on_setattr(inode))
-		pnfs_return_layout(inode);
+		pnfs_commit_and_return_layout(inode);
 
 	nfs_fattr_init(fattr);
 	

fs/nfs/pnfs.c

@@ -866,6 +866,33 @@ _pnfs_return_layout(struct inode *ino)
 }
 EXPORT_SYMBOL_GPL(_pnfs_return_layout);
 
+int
+pnfs_commit_and_return_layout(struct inode *inode)
+{
+	struct pnfs_layout_hdr *lo;
+	int ret;
+
+	spin_lock(&inode->i_lock);
+	lo = NFS_I(inode)->layout;
+	if (lo == NULL) {
+		spin_unlock(&inode->i_lock);
+		return 0;
+	}
+	pnfs_get_layout_hdr(lo);
+	/* Block new layoutgets and read/write to ds */
+	lo->plh_block_lgets++;
+	spin_unlock(&inode->i_lock);
+	filemap_fdatawait(inode->i_mapping);
+	ret = pnfs_layoutcommit_inode(inode, true);
+	if (ret == 0)
+		ret = _pnfs_return_layout(inode);
+	spin_lock(&inode->i_lock);
+	lo->plh_block_lgets--;
+	spin_unlock(&inode->i_lock);
+	pnfs_put_layout_hdr(lo);
+	return ret;
+}
+
 bool pnfs_roc(struct inode *ino)
 {
 	struct pnfs_layout_hdr *lo;

fs/nfs/pnfs.h

@@ -219,6 +219,7 @@ void pnfs_set_layoutcommit(struct nfs_write_data *wdata);
 void pnfs_cleanup_layoutcommit(struct nfs4_layoutcommit_data *data);
 int pnfs_layoutcommit_inode(struct inode *inode, bool sync);
 int _pnfs_return_layout(struct inode *);
+int pnfs_commit_and_return_layout(struct inode *);
 void pnfs_ld_write_done(struct nfs_write_data *);
 void pnfs_ld_read_done(struct nfs_read_data *);
 struct pnfs_layout_segment *pnfs_update_layout(struct inode *ino,
@@ -407,6 +408,11 @@ static inline int pnfs_return_layout(struct inode *ino)
 	return 0;
 }
 
+static inline int pnfs_commit_and_return_layout(struct inode *inode)
+{
+	return 0;
+}
+
 static inline bool
 pnfs_ld_layoutret_on_setattr(struct inode *inode)
 {