linux-kernel - Re: [PATCH 3/3] tty_lock: Localise the lock

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Message-ID: <CA+1xoqezLCQh_fqJ1iNAs25X7Fm24W=-0J8zTZuVVJQnWTtSLg@mail.gmail.com>
Date:	Mon, 7 May 2012 18:03:07 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH 3/3] tty_lock: Localise the lock

Hi Alan,

On Thu, May 3, 2012 at 11:24 PM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
> index 5505ffc..d6fa842 100644
> --- a/drivers/tty/pty.c
> +++ b/drivers/tty/pty.c
> @@ -62,9 +63,7 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
>                        mutex_unlock(&devpts_mutex);
>                }
>  #endif
> -               tty_unlock();
>                tty_vhangup(tty->link);
> -               tty_lock();
>        }
>  }

I don't believe that this change is correct.

Consider the following scenario:

tty_release -> tty_lock -> pty_close -> tty_vhangup -> tty_lock

Which would cause a deadlock.
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