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From: Sasha Levin <levinsasha928@gmail.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org
Subject: Re: [PATCH 3/3] tty_lock: Localise the lock
Date: Mon, 7 May 2012 18:03:07 +0200	[thread overview]
Message-ID: <CA+1xoqezLCQh_fqJ1iNAs25X7Fm24W=-0J8zTZuVVJQnWTtSLg@mail.gmail.com> (raw)
In-Reply-To: <20120503212219.568.15653.stgit@bob.linux.org.uk>

Hi Alan,

On Thu, May 3, 2012 at 11:24 PM, Alan Cox <alan@lxorguk.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.

WARNING: multiple messages have this Message-ID (diff)
From: Sasha Levin <levinsasha928@gmail.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org
Subject: Re: [PATCH 3/3] tty_lock: Localise the lock
Date: Mon, 7 May 2012 18:03:07 +0200	[thread overview]
Message-ID: <CA+1xoqezLCQh_fqJ1iNAs25X7Fm24W=-0J8zTZuVVJQnWTtSLg@mail.gmail.com> (raw)
In-Reply-To: <20120503212219.568.15653.stgit@bob.linux.org.uk>

Hi Alan,

On Thu, May 3, 2012 at 11:24 PM, Alan Cox <alan@lxorguk.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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  parent reply	other threads:[~2012-05-07 16:03 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-05-03 21:21 [PATCH 1/3] tty_lock: undo the old tty_lock use on the ctty Alan Cox
2012-05-03 21:22 ` [PATCH 2/3] pty: Lock the devpts bits privately Alan Cox
2012-05-08 18:18   ` H. Peter Anvin
2012-05-08 20:43     ` Alan Cox
2012-05-08 20:41       ` H. Peter Anvin
2012-05-03 21:24 ` [PATCH 3/3] tty_lock: Localise the lock Alan Cox
2012-05-04 20:48   ` Arnd Bergmann
2012-05-04 23:54   ` Greg KH
2012-05-04 23:55     ` Greg KH
2012-05-07 16:03   ` Sasha Levin [this message]
2012-05-07 16:03     ` Sasha Levin
2012-05-07 16:11     ` Alan Cox
2012-05-07 16:30       ` Sasha Levin
2012-05-07 16:42         ` Alan Cox
2012-05-07 17:00           ` Sasha Levin
2012-05-07 21:04             ` Jiri Slaby
2012-05-08 18:12               ` Sasha Levin
2012-05-11 10:40                 ` Sasha Levin
2012-05-11 14:52                   ` Greg KH
2012-05-11 15:09                     ` Sasha Levin
2012-05-11 15:09                       ` Sasha Levin

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