CIFS: Fix persistent handles re-opening on reconnect

openFileList of tcon can be changed while cifs_reopen_file() is called
that can lead to an unexpected behavior when we return to the loop.
Fix this by introducing a temp list for keeping all file handles that
need to be reopen.
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/cifsglob.h

@@ -1065,6 +1065,7 @@ struct cifsFileInfo {
 	kuid_t uid;		/* allows finding which FileInfo structure */
 	__u32 pid;		/* process id who opened file */
 	struct cifs_fid fid;	/* file id from remote */
+	struct list_head rlist; /* reconnect list */
 	/* BB add lock scope info here if needed */ ;
 	/* lock scope id (0 if none) */
 	struct dentry *dentry;

fs/cifs/file.c

@@ -763,19 +763,31 @@ int cifs_close(struct inode *inode, struct file *file)
 void
 cifs_reopen_persistent_handles(struct cifs_tcon *tcon)
 {
-	struct cifsFileInfo *open_file = NULL;
+	struct cifsFileInfo *open_file;
 	struct list_head *tmp;
 	struct list_head *tmp1;
+	struct list_head tmp_list;
+
+	cifs_dbg(FYI, "Reopen persistent handles");
+	INIT_LIST_HEAD(&tmp_list);
 
 	/* list all files open on tree connection, reopen resilient handles  */
 	spin_lock(&tcon->open_file_lock);
-	list_for_each_safe(tmp, tmp1, &tcon->openFileList) {
+	list_for_each(tmp, &tcon->openFileList) {
 		open_file = list_entry(tmp, struct cifsFileInfo, tlist);
-		spin_unlock(&tcon->open_file_lock);
-		cifs_reopen_file(open_file, false /* do not flush */);
-		spin_lock(&tcon->open_file_lock);
+		if (!open_file->invalidHandle)
+			continue;
+		cifsFileInfo_get(open_file);
+		list_add_tail(&open_file->rlist, &tmp_list);
 	}
 	spin_unlock(&tcon->open_file_lock);
+
+	list_for_each_safe(tmp, tmp1, &tmp_list) {
+		open_file = list_entry(tmp, struct cifsFileInfo, rlist);
+		cifs_reopen_file(open_file, false /* do not flush */);
+		list_del_init(&open_file->rlist);
+		cifsFileInfo_put(open_file);
+	}
 }
 
 int cifs_closedir(struct inode *inode, struct file *file)