CIFS: Fix a possible double locking of mutex during reconnect

With the current code it is possible to lock a mutex twice when
a subsequent reconnects are triggered. On the 1st reconnect we
reconnect sessions and tcons and then persistent file handles.
If the 2nd reconnect happens during the reconnecting of persistent
file handles then the following sequence of calls is observed:

cifs_reopen_file -> SMB2_open -> small_smb2_init -> smb2_reconnect
-> cifs_reopen_persistent_file_handles -> cifs_reopen_file (again!).

So, we are trying to acquire the same cfile->fh_mutex twice which
is wrong. Fix this by moving reconnecting of persistent handles to
the delayed work (smb2_reconnect_server) and submitting this work
every time we reconnect tcon in SMB2 commands handling codepath.

This can also lead to corruption of a temporary file list in
cifs_reopen_persistent_file_handles() because we can recursively
call this function twice.

Cc: Stable <stable@vger.kernel.org> # v4.9+
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>

fs/cifs/cifsglob.h

@@ -926,6 +926,7 @@ struct cifs_tcon {
 	bool broken_posix_open; /* e.g. Samba server versions < 3.3.2, 3.2.9 */
 	bool broken_sparse_sup; /* if server or share does not support sparse */
 	bool need_reconnect:1; /* connection reset, tid now invalid */
+	bool need_reopen_files:1; /* need to reopen tcon file handles */
 	bool use_resilient:1; /* use resilient instead of durable handles */
 	bool use_persistent:1; /* use persistent instead of durable handles */
 #ifdef CONFIG_CIFS_SMB2

fs/cifs/file.c

@@ -777,6 +777,11 @@ cifs_reopen_persistent_handles(struct cifs_tcon *tcon)
 	struct list_head *tmp1;
 	struct list_head tmp_list;
 
+	if (!tcon->use_persistent || !tcon->need_reopen_files)
+		return;
+
+	tcon->need_reopen_files = false;
+
 	cifs_dbg(FYI, "Reopen persistent handles");
 	INIT_LIST_HEAD(&tmp_list);
 
@@ -793,7 +798,8 @@ cifs_reopen_persistent_handles(struct cifs_tcon *tcon)
 
 	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 */);
+		if (cifs_reopen_file(open_file, false /* do not flush */))
+			tcon->need_reopen_files = true;
 		list_del_init(&open_file->rlist);
 		cifsFileInfo_put(open_file);
 	}

fs/cifs/smb2pdu.c

@@ -250,16 +250,19 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon)
 	}
 
 	cifs_mark_open_files_invalid(tcon);
+	if (tcon->use_persistent)
+		tcon->need_reopen_files = true;
 
 	rc = SMB2_tcon(0, tcon->ses, tcon->treeName, tcon, nls_codepage);
 	mutex_unlock(&tcon->ses->session_mutex);
 
-	if (tcon->use_persistent)
-		cifs_reopen_persistent_handles(tcon);
-
 	cifs_dbg(FYI, "reconnect tcon rc = %d\n", rc);
 	if (rc)
 		goto out;
+
+	if (smb2_command != SMB2_INTERNAL_CMD)
+		queue_delayed_work(cifsiod_wq, &server->reconnect, 0);
+
 	atomic_inc(&tconInfoReconnectCount);
 out:
 	/*
@@ -1990,7 +1993,7 @@ void smb2_reconnect_server(struct work_struct *work)
 	spin_lock(&cifs_tcp_ses_lock);
 	list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list) {
 		list_for_each_entry(tcon, &ses->tcon_list, tcon_list) {
-			if (tcon->need_reconnect) {
+			if (tcon->need_reconnect || tcon->need_reopen_files) {
 				tcon->tc_count++;
 				list_add_tail(&tcon->rlist, &tmp_list);
 				tcon_exist = true;
@@ -2007,7 +2010,8 @@ void smb2_reconnect_server(struct work_struct *work)
 	spin_unlock(&cifs_tcp_ses_lock);
 
 	list_for_each_entry_safe(tcon, tcon2, &tmp_list, rlist) {
-		smb2_reconnect(SMB2_ECHO, tcon);
+		if (!smb2_reconnect(SMB2_INTERNAL_CMD, tcon))
+			cifs_reopen_persistent_handles(tcon);
 		list_del_init(&tcon->rlist);
 		cifs_put_tcon(tcon);
 	}

fs/cifs/smb2pdu.h

@@ -80,6 +80,8 @@
 #define SMB2_SET_INFO		cpu_to_le16(SMB2_SET_INFO_HE)
 #define SMB2_OPLOCK_BREAK	cpu_to_le16(SMB2_OPLOCK_BREAK_HE)
 
+#define SMB2_INTERNAL_CMD	cpu_to_le16(0xFFFF)
+
 #define NUMBER_OF_SMB2_COMMANDS	0x0013
 
 /* BB FIXME - analyze following length BB */