linux-kernel - Re: [PATCH v2 09/19] staging/speakup: Use tty_ldisc

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Date:	Sun, 10 Jan 2016 16:25:17 -0800
From:	Peter Hurley <peter@...leysoftware.com>
To:	Ben Hutchings <ben@...adent.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH v2 09/19] staging/speakup: Use tty_ldisc_ref() for paste
 kworker

On 01/10/2016 03:16 PM, Ben Hutchings wrote:
> On Sat, 2016-01-09 at 20:41 -0800, Peter Hurley wrote:
>> As the function documentation for tty_ldisc_ref_wait() notes, it is
>> only callable from a tty file_operations routine; otherwise there
>> is no guarantee the ref won't be NULL.
>>
>> The key difference with the VT's paste_selection() is that is an ioctl,
>> where __speakup_paste_selection() is completely asynch kworker, kicked
>> off from interrupt context.
>>
>> Fixes: 28a821c30688 ("Staging: speakup: Update __speakup_paste_selection()
>>        tty (ab)usage to match vt")
>> Cc: <stable@...r.kernel.org>
>>
>> Signed-off-by: Peter Hurley <peter@...leysoftware.com>
>> ---
>>  drivers/staging/speakup/selection.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/staging/speakup/selection.c b/drivers/staging/speakup/selection.c
>> index aa5ab6c..86c0b9a 100644
>> --- a/drivers/staging/speakup/selection.c
>> +++ b/drivers/staging/speakup/selection.c
>> @@ -142,7 +142,9 @@ static void __speakup_paste_selection(struct work_struct *work)
>>  	struct tty_ldisc *ld;
>>  	DECLARE_WAITQUEUE(wait, current);
>>  
>> -	ld = tty_ldisc_ref_wait(tty);
>> +	ld = tty_ldisc_ref(tty);
>> +	if (!ld)
>> +		return;
>>  	tty_buffer_lock_exclusive(&vc->port);
>>  
>>  	add_wait_queue(&vc->paste_wait, &wait);
> 
> This leaks a reference to the tty.  Instead of returning directly, I
> think you need to add a label and goto the tty_kref_put() at the bottom
> of the function.

Ugh, speakup_paste_selection() is a worse hack than I thought it was.