çå: [PATCH][v2] tty: fix race between flush_to_ldisc and tty_open

[Li,Rongqing]

> -----éäåä-----
> åää: Kohli, Gaurav [mailto:gkohli@xxxxxxxxxxxxxx]
> åéæé: 2019å1æ11æ 21:57
> æää: Li,Rongqing <lirongqing@xxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx;
> jslaby@xxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; alan@xxxxxxxxxxxxxxx
> äé: Re: [PATCH][v2] tty: fix race between flush_to_ldisc and tty_open
> 
> Hi,
> 
> it don't seems to be good idea to put lock on one function and unlock in some
> other function. If in future some one has to call tty_init_dev, how he can track
> the unlocking as well of ldisc lock.
> 
> Regards
> Gaurav
> 

This similar condition has existed for a long time, tty_unlock(tty) must be called in
some other functions who call tty_init_dev, since tty_init_dev hold tty_lock, and does
not release it

so I think it is user responsibility to fully understand tty_init_dev; and I can add some 
comments for tty_init_dev if this patch can be acceptable;


or a workaround like below:
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index a42a028a9d4e..2f5ad256b6ad 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -425,7 +425,7 @@ static void flush_to_ldisc(struct work_struct *work)
        struct tty_ldisc *disc;
 
        tty = port->itty;
-       if (tty == NULL)
+       if (tty == NULL || tty->driver_data == NULL)
                return;
 
        disc = tty_ldisc_ref(tty);

thanks

-RongQing