linux-kernel - 答复: [PATCH][v2] tty: fix race between flush_to_ldisc and tty

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Date:   Mon, 14 Jan 2019 02:51:34 +0000
From:   "Li,Rongqing" <lirongqing@...du.com>
To:     "Kohli, Gaurav" <gkohli@...eaurora.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jslaby@...e.com" <jslaby@...e.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "alan@...ux.intel.com" <alan@...ux.intel.com>
Subject: 答复: [PATCH][v2] tty: fix race between flush_to_ldisc and tty_open

> -----邮件原件-----
> 发件人: Kohli, Gaurav [mailto:gkohli@...eaurora.org]
> 发送时间: 2019年1月11日 21:57
> 收件人: Li,Rongqing <lirongqing@...du.com>; linux-kernel@...r.kernel.org;
> jslaby@...e.com; gregkh@...uxfoundation.org; alan@...ux.intel.com
> 主题: 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