linux-kernel - Re: [PATCH v2 1/1] Char: tty, fix tty_port_block_til

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Message-Id: <20090623163006.f05b75ee.akpm@linux-foundation.org>
Date:	Tue, 23 Jun 2009 16:30:06 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	alan@...rguk.ukuu.org.uk, linux-kernel@...r.kernel.org,
	jirislaby@...il.com
Subject: Re: [PATCH v2 1/1] Char: tty, fix tty_port_block_til_ready waiting

On Thu, 18 Jun 2009 09:46:13 +0200
Jiri Slaby <jirislaby@...il.com> wrote:

> Use DEFINE_WAIT instead DECLARE_WAITQUEUE, because we use
> prepare/finish_wait since commit
> 3e3b5c087799e536871c8261b05bc28e4783c8da
> (tty: use prepare/finish_wait)
> 
> Otherwise we would oops in finish_wait.
> 

<scratches head for a while>

OK, here's a better changelog:

   Since commit 3e3b5c087799e536871c8261b05bc28e4783c8da ("tty: use
   prepare/finish_wait"), tty_port_block_til_ready() is using
   prepare_to_wait()/finish_wait().  Those functions require that
   the wait_queue_t be initialised with .func=autoremove_wake_function,
   via DEFINE_WAIT().

   But the conversion from DECLARE_WAITQUEUE() to DEFINE_WAIT() was
   not made, so this code will oops in finish_wait().

> 
> diff --git a/drivers/char/tty_port.c b/drivers/char/tty_port.c
> index 62dadfc..4e862a7 100644
> --- a/drivers/char/tty_port.c
> +++ b/drivers/char/tty_port.c
> @@ -193,7 +193,7 @@ int tty_port_block_til_ready(struct tty_port *port,
>  {
>  	int do_clocal = 0, retval;
>  	unsigned long flags;
> -	DECLARE_WAITQUEUE(wait, current);
> +	DEFINE_WAIT(wait);
>  	int cd;
>  
>  	/* block if port is in the process of being closed */

Why is nobody reporting the oopses?
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