linux-kernel - Re: [PATCH RESEND] tty: don't dead lock while flushing workqueue

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Date:	Wed, 05 Dec 2012 17:15:40 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Peter Hurley <peter@...leysoftware.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	Alan Cox <alan@...ux.intel.com>
Subject: Re: [PATCH RESEND] tty: don't dead lock while flushing workqueue

On 12/03/2012 06:41 PM, Peter Hurley wrote:
> The lock logic for tty_set_ldisc() is wrong. Despite existing code in
> tty_set_ldisc() and tty_ldisc_hangup(), the ldisc_mutex does **not**
> (and should not) play a role in acquiring or releasing ldisc references.
> The only thing that needs to happen here is below (don't actually use
> below because I just hand-edited it):

Hmm. What about I stay in sync with the code that is already in tree
and if the wrong locking gets removed in both places later on?

Alan, what do you prefer?

>> See http://lkml.org/lkml/2012/11/21/347
>>
>>   drivers/tty/tty_ldisc.c |   13 +++++++++----
>>   1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
>> index 0f2a2c5..fb76818 100644
>> --- a/drivers/tty/tty_ldisc.c
>> +++ b/drivers/tty/tty_ldisc.c
>> @@ -930,16 +930,21 @@ void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
>>   	 */
>>
>> - 	tty_lock_pair(tty, o_tty);
>>   	tty_ldisc_halt(tty);
>> 	tty_ldisc_flush_works(tty);
>
>
>> +	tty_lock_pair(tty, o_tty);
>>   	/* This will need doing differently if we need to lock */
>>   	tty_ldisc_kill(tty);
>> -
>>   	if (o_tty)
>>   		tty_ldisc_kill(o_tty);
>>

Sebastian
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