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From: Xie He <>
To: Gao Yan <>
Subject: Re: [PATCH] net: remove disc_data_lock in ppp line discipline
Date: Fri, 01 Jan 2021 01:37:44 +0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

> In tty layer, it use tty->ldisc_sem to proect tty_ldisc_ops.
> So I think tty->ldisc_sem can also protect tty->disc_data;

It might help by CC'ing TTY people, so that we could get this reviewed by
people who are familiar with TTY code.

Greg Kroah-Hartman <> (supporter:TTY LAYER)
Jiri Slaby <> (supporter:TTY LAYER)


> For examlpe,
> When cpu A is running ppp_synctty_ioctl that hold the tty->ldisc_sem,
> at the same time  if cpu B calls ppp_synctty_close, it will wait until
> cpu A release tty->ldisc_sem. So I think it is unnecessary to have the
> disc_data_lock;
> cpu A                           cpu B
> tty_ioctl                       tty_reopen
>  ->hold tty->ldisc_sem            ->hold tty->ldisc_sem(write), failed
>  ->ld->ops->ioctl                 ->wait...
>  ->release tty->ldisc_sem         ->wait...OK,hold tty->ldisc_sem
>                                     ->tty_ldisc_reinit
>                                       ->tty_ldisc_close
>                                         ->ld->ops->close

IMHO an example might not be necessary. Examples are useful to show
incorrectness. But we cannot show correctness by examples because
examples are not exhaustive.

BTW, there're some typos:
"proect" -> "protect"
"examlpe" -> "example"
"that hold ..." -> "that holds ..."
"cpu A release ..." -> "cpu A releases ..."

>   * FIXME: this is no longer true. The _close path for the ldisc is
>   * now guaranteed to be sane.
>   */

>   *
>   * FIXME: Fixed in tty_io nowadays.
>   */

Since you are removing "disc_data_lock", please update (or remove) these
two comments. Thanks!

      parent reply	other threads:[~2021-01-01  1:37 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-28  7:15 Gao Yan
2020-12-31 10:00 ` 答复: [PATCH] net: remove disc_data_lock in =?utf-8?Q?_ppp_line_discipl Gaoyan
2021-01-01  1:37 ` Xie He [this message]

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