fix oops in heavy stress test caused by lack of check for bad dentry being passed in on reconnect

fs/cifs/dir.c

@@ -38,7 +38,7 @@ renew_parental_timestamps(struct dentry *direntry)
 	do {
 		direntry->d_time = jiffies;
 		direntry = direntry->d_parent;
-	} while (!IS_ROOT(direntry));	/* BB for DFS case should stop at the root of share which could be lower than root of this mount due to implicit dfs connections */
+	} while (!IS_ROOT(direntry));	
 }
 
 /* Note: caller must free return buffer */
@@ -49,6 +49,11 @@ build_path_from_dentry(struct dentry *direntry)
 	int namelen = 0;
 	char *full_path;
 
+	if(direntry == NULL)
+		return NULL;  /* not much we can do if dentry is freed and
+		we need to reopen the file after it was closed implicitly
+		when the server crashed */
+
 	for (temp = direntry; !IS_ROOT(temp);) {
 		namelen += (1 + temp->d_name.len);
 		temp = temp->d_parent;

fs/cifs/file.c

@@ -283,7 +283,12 @@ static int cifs_reopen_file(struct inode *inode, struct file *file)
 		return 0;
 	}
 
-
+	if(file->f_dentry == NULL) {
+		up(&pCifsFile->fh_sem);
+		cFYI(1,("failed file reopen, no valid name if dentry freed"));
+		FreeXid(xid);
+		return -EBADF;
+	}
 	cifs_sb = CIFS_SB(inode->i_sb);
 	pTcon = cifs_sb->tcon;