From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1427266AbcBSIX4 (ORCPT ); Fri, 19 Feb 2016 03:23:56 -0500 Received: from mail-wm0-f43.google.com ([74.125.82.43]:35164 "EHLO mail-wm0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1427182AbcBSIXl (ORCPT ); Fri, 19 Feb 2016 03:23:41 -0500 MIME-Version: 1.0 In-Reply-To: <56C6C7E3.4060200@samsung.com> References: <1455817202-3005-1-git-send-email-linux.amoon@gmail.com> <56C603E9.9050307@hurleysoftware.com> <56C6C7E3.4060200@samsung.com> From: Anand Moon Date: Fri, 19 Feb 2016 13:53:19 +0530 Message-ID: Subject: Re: [PATCH] serial: samsung: fix the inconsistency in spinlock To: Krzysztof Kozlowski Cc: Peter Hurley , Greg Kroah-Hartman , Jiri Slaby , linux-serial@vger.kernel.org, "linux-samsung-soc@vger.kernel.org" , Linux Kernel Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Krzysztof, On 19 February 2016 at 13:14, Krzysztof Kozlowski wrote: > On 19.02.2016 15:51, Anand Moon wrote: >> Hi Krzysztof, >> >> On 19 February 2016 at 11:39, Krzysztof Kozlowski >> wrote: >>> 2016-02-19 4:14 GMT+09:00 Anand Moon : >>>> Hi Peter, >>>> >>>> On 18 February 2016 at 23:18, Peter Hurley wrote: >>>>> Hi Anand, >>>>> >>>>> On 02/18/2016 09:40 AM, Anand Moon wrote: >>>>>> From: Anand Moon >>>>>> >>>>>> changes fix the correct order of the spin_lock_irqrestore/save. >>>>>> >>>>>> Signed-off-by: Anand Moon >>>>>> --- >>>>>> 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 >> >> Yes I understood the meaning of the sentence. Already the >> s3c24xx_serial_tx_chars function. >> holds the lock port->lock for safe IRQ execution. > > I am sorry but I don't get your explanation. I mentioned Peter's > thoughts about lockups after adding locking over uart_write(). However > you are referring to s3c24xx_serial_tx_chars() holding the spin lock... > I am missing the point... > > Best regards, > Krzysztof > I should be sorry I could not explain you in technical terms. Interrupt routine already hold the port->lock s3c24xx_serial_tx_chars \ spin_lock_irqsave(&port->lock, flags); \... spin_unlock(&port->lock); uart_write_wakeup(port); spin_lock(&port->lock); \ spin_unlock_irqrestore(&port->lock, flags); In my next patch I have tried to remove the spin_unlock/spin_lock over uart_write_wakeup(port); Best Regards. -Anand Moon