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SubjectRe: [PATCH 1/2] serial: 8250: Fix autoconfig_irq() to avoid race conditions
Date
On 2015/07/24 7:32, gregkh@linuxfoundation.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@cp.jp.nec.com>
>> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
>> Reviewed-by: Peter Hurley <peter@hurleysoftware.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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