linux-kernel - Re: [PATCH 0/2] serial: 8250: Workaround to avoid irq=0 for console

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Date:	Tue, 7 Jul 2015 08:13:59 +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 0/2] serial: 8250: Workaround to avoid irq=0 for console

On 2015/06/05 18:55, Taichi Kageyama wrote:
> This patch set provides a workaround to avoid the following problem.
> It's based on Linux 4.1-rc3 mainstream kernel.
> I've tested this patch set on x86-64 machine and KVM.
>
> Problem
> --------------------------
> There're cases where autoconfig_irq() fails during boot.
> In these cases, 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.
> I saw the original problem on RHEL6.6.
>
> Fix
> --------------------------
> serial: 8250: Fix autoconfig_irq() to avoid race conditions
>   Fix one of autoconfig_irq() failure case.
> serial: 8250: Allow to skip autoconfig_irq() for a console
>   Provide a workaround to avoid other autoconfig_irq() failure cases.
>
> Conditions of Reproduction
> --------------------------
> - Build with CONFIG_SERIAL_8250_DETECT_IRQ.
> - Need non-PnP console serial or PnP console with no CONFIG_SERIAL_8250_PNP
> - Kick printk() repeatedly on the CPU which can handle an interrupt
>    from a console serial during autoconfig_irq(). The CPU is basically cpu0.
> - Disable the interrupt of the CPU for longer during autoconfig_irq().
>
> Note
> --------------------------
> Ideally, I think autoconfig_irq() should be fixed completely,
> but it's hard from the following points
> as long as auto_irq algorithm is used.
>   - How long it should wait for an interrrupt
>   - How to assure the interrupt of the CPU enabled during auto_irq
>   - How to know which CPU can handle an interrupt from a serial.
>
> Do you have any other idea?
> In my opinion, providing a workaround is better than
> applying big changes to the old function for legacy devices.
>
> Taichi Kageyama (2):
>    serial: 8250: Fix autoconfig_irq() to avoid race conditions
>    serial: 8250: Allow to skip autoconfig_irq() for a console
>
>   drivers/tty/serial/8250/8250_core.c |   23 +++++++++++++++++++++++
>   1 files changed, 23 insertions(+), 0 deletions(-)
>

Could you review this patch set?


Thanks,
Taichi