fs/9p: Writeback dirty data before setattr

change file attribute can result in making the file readonly.
So flush the dirty pages before that.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

fs/9p/vfs_inode.c

@@ -999,6 +999,10 @@ static int v9fs_vfs_setattr(struct dentry *dentry, struct iattr *iattr)
 		if (retval)
 			return retval;
 	}
+	/* Write all dirty data */
+	if (S_ISREG(dentry->d_inode->i_mode))
+		filemap_write_and_wait(dentry->d_inode->i_mapping);
+
 	retval = p9_client_wstat(fid, &wstat);
 	if (retval < 0)
 		return retval;

fs/9p/vfs_inode_dotl.c

@@ -459,6 +459,10 @@ int v9fs_vfs_setattr_dotl(struct dentry *dentry, struct iattr *iattr)
 		if (retval)
 			return retval;
 	}
+	/* Write all dirty data */
+	if (S_ISREG(dentry->d_inode->i_mode))
+		filemap_write_and_wait(dentry->d_inode->i_mapping);
+
 	retval = p9_client_setattr(fid, &p9attr);
 	if (retval < 0)
 		return retval;