linux-kernel - Re: [PATCH] serial: samsung: fix the inconsistency in spinlock

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Date:	Fri, 19 Feb 2016 15:09:59 +0900
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Anand Moon <linux.amoon@...il.com>
Cc:	Peter Hurley <peter@...leysoftware.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>, linux-serial@...r.kernel.org,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] serial: samsung: fix the inconsistency in spinlock

2016-02-19 4:14 GMT+09:00 Anand Moon <linux.amoon@...il.com>:
> Hi Peter,
>
> On 18 February 2016 at 23:18, Peter Hurley <peter@...leysoftware.com> wrote:
>> Hi Anand,
>>
>> On 02/18/2016 09:40 AM, Anand Moon wrote:
>>> From: Anand Moon <linux.amoon@...il.com>
>>>
>>> changes fix the correct order of the spin_lock_irqrestore/save.
>>>
>>> Signed-off-by: Anand Moon <linux.amoon@...il.com>
>>> ---
>>>  drivers/tty/serial/samsung.c | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/tty/serial/samsung.c b/drivers/tty/serial/samsung.c
>>> index d72cd73..96fe14d 100644
>>> --- a/drivers/tty/serial/samsung.c
>>> +++ b/drivers/tty/serial/samsung.c
>>> @@ -759,9 +759,9 @@ static irqreturn_t s3c24xx_serial_tx_chars(int irq, void *id)
>>>       }
>>>
>>>       if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS) {
>>> -             spin_unlock(&port->lock);
>>> +             spin_unlock_irqrestore(&port->lock, flags);
>>>               uart_write_wakeup(port);
>>> -             spin_lock(&port->lock);
>>> +             spin_lock_irqsave(&port->lock, flags);
>>
>> This driver shouldn't be dropping the spin lock at for write wakeup.
>> If this is causing lock-ups in a line discipline, the line discipline
>> needs fixed.
>>
>
> Thanks for pointing out.
> Their is no lock up, just the inconstancy of the spin_lock.
> Then I will resend this patch dropping the spin_unlock/spin_lock
> around uart_write_wakeup.
> Is that ok with you.

Anand, before doing that, can you check Peter's second sentence? I
mean the "If this is causing lock-ups in a line discipline, the line
discipline needs fixed.".
Don't drop the spin-locks "just because". I would be happy to see more
detailed explanation in changelog.

Best regards,
Krzysztof