smb3: fix unusable share after force unmount failure

If user does forced unmount ("umount -f") while files are still open
on the share (as was seen in a Kubernetes example running on SMB3.1.1
mount) then we were marking the share as "TID_EXITING" in umount_begin()
which caused all subsequent operations (except write) to fail ... but
unfortunately when umount_begin() is called we do not know yet that
there are open files or active references on the share that would prevent
unmount from succeeding.  Kubernetes had example when they were doing
umount -f when files were open which caused the share to become
unusable until the files were closed (and the umount retried).

Fix this so that TID_EXITING is not set until we are about to send
the tree disconnect (not at the beginning of forced umounts in
umount_begin) so that if "umount -f" fails (due to open files or
references) the mount is still usable.

Cc: stable@vger.kernel.org
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifsfs.c

@@ -731,13 +731,16 @@ static void cifs_umount_begin(struct super_block *sb)
 	spin_lock(&tcon->tc_lock);
 	if ((tcon->tc_count > 1) || (tcon->status == TID_EXITING)) {
 		/* we have other mounts to same share or we have
-		   already tried to force umount this and woken up
+		   already tried to umount this and woken up
 		   all waiting network requests, nothing to do */
 		spin_unlock(&tcon->tc_lock);
 		spin_unlock(&cifs_tcp_ses_lock);
 		return;
-	} else if (tcon->tc_count == 1)
-		tcon->status = TID_EXITING;
+	}
+	/*
+	 * can not set tcon->status to TID_EXITING yet since we don't know if umount -f will
+	 * fail later (e.g. due to open files).  TID_EXITING will be set just before tdis req sent
+	 */
 	spin_unlock(&tcon->tc_lock);
 	spin_unlock(&cifs_tcp_ses_lock);
 

fs/cifs/cifssmb.c

@@ -86,13 +86,11 @@ cifs_reconnect_tcon(struct cifs_tcon *tcon, int smb_command)
 
 	/*
 	 * only tree disconnect, open, and write, (and ulogoff which does not
-	 * have tcon) are allowed as we start force umount
+	 * have tcon) are allowed as we start umount
 	 */
 	spin_lock(&tcon->tc_lock);
 	if (tcon->status == TID_EXITING) {
-		if (smb_command != SMB_COM_WRITE_ANDX &&
-		    smb_command != SMB_COM_OPEN_ANDX &&
-		    smb_command != SMB_COM_TREE_DISCONNECT) {
+		if (smb_command != SMB_COM_TREE_DISCONNECT) {
 			spin_unlock(&tcon->tc_lock);
 			cifs_dbg(FYI, "can not send cmd %d while umounting\n",
 				 smb_command);

fs/cifs/connect.c

@@ -2324,6 +2324,7 @@ cifs_put_tcon(struct cifs_tcon *tcon)
 	WARN_ON(tcon->tc_count < 0);
 
 	list_del_init(&tcon->tcon_list);
+	tcon->status = TID_EXITING;
 	spin_unlock(&tcon->tc_lock);
 	spin_unlock(&cifs_tcp_ses_lock);
 

fs/cifs/smb2pdu.c

@@ -165,13 +165,9 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
 	spin_lock(&tcon->tc_lock);
 	if (tcon->status == TID_EXITING) {
 		/*
-		 * only tree disconnect, open, and write,
-		 * (and ulogoff which does not have tcon)
-		 * are allowed as we start force umount.
+		 * only tree disconnect allowed when disconnecting ...
 		 */
-		if ((smb2_command != SMB2_WRITE) &&
-		   (smb2_command != SMB2_CREATE) &&
-		   (smb2_command != SMB2_TREE_DISCONNECT)) {
+		if (smb2_command != SMB2_TREE_DISCONNECT) {
 			spin_unlock(&tcon->tc_lock);
 			cifs_dbg(FYI, "can not send cmd %d while umounting\n",
 				 smb2_command);