linux-kernel - Re: [PATCH 1/2] serial: 8250: Fix autoconfig

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Message-ID: <55B88B38.4070703@cp.jp.nec.com>
Date:	Wed, 29 Jul 2015 08:13:44 +0000
From:	Taichi Kageyama <t-kageyama@...jp.nec.com>
To:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"jslaby@...e.cz" <jslaby@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"prarit@...hat.com" <prarit@...hat.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Subject: Re: [PATCH 1/2] serial: 8250: Fix autoconfig_irq() to avoid race
 conditions

On 2015/07/24 7:32, gregkh@...uxfoundation.org wrote:
> On Fri, Jun 05, 2015 at 09:57:40AM +0000, Taichi Kageyama wrote:
>> The following race conditions can happen if a serial is used as console.
>>   Case1. CPU_B handles an interrupt from a serial
>>     autoconfig_irq() fails whether the interrupt is raised or not
>>     if CPU_B is disabled to handle interrupts for longer than it expects.
>>   Case2. CPU_B clears UART_IER just after CPU_A sets UART_IER
>>     A serial may not make an interrupt.
>>     autoconfig_irq() can fail if the interrupt is not raised.
>>   Case3. CPU_A sets UART_IER just after CPU_B clears UART_IER
>>     This is an unexpected behavior for uart_console_write().
>>
>>   CPU_A [autoconfig_irq]      CPU_B [serial8250_console_write]
>>   -----------------------------------------------------------------
>>   probe_irq_on()              spin_lock_irqsave(&port->lock,)
>>   serial_outp(,UART_IER,0x0f) serial_out(,UART_IER,0)
>>   udelay(20);                 uart_console_write()
>>   probe_irq_off()
>>                               spin_unlock_irqrestore(&port->lock,)
>>   -----------------------------------------------------------------
>>
>> If autoconfig_irq() fails, the console doesn't work in interrupt mode,
>> the mode cannot be changed anymore, and "input overrun"
>> (which can make operation mistakes) happens easily.
>> This problem happens with high rate every boot once it occurs
>> because the boot sequence is always almost same.
>>
>> Signed-off-by: Taichi Kageyama <t-kageyama@...jp.nec.com>
>> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
>> Reviewed-by: Peter Hurley <peter@...leysoftware.com>
>> ---
>>   drivers/tty/serial/8250/8250_core.c |    6 ++++++
>>   1 files changed, 6 insertions(+), 0 deletions(-)
> 
> Does not apply to 4.2-rc3 :(
> 

Sorry for the trouble and late reply.
It's my fault. It was encoded as base64 by Exchange.
I sent new patch set including this patch.
I updated commit log.


Regards,
Taichi--
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