linux-kernel - Re: [PATCH 0/2] nbcon locking issue with v6.6.10-rt18 kernel

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Message-ID: <87o7db9ihv.fsf@jogness.linutronix.de>
Date: Wed, 24 Jan 2024 10:46:44 +0106
From: John Ogness <john.ogness@...utronix.de>
To: Junxiao Chang <junxiao.chang@...el.com>, bigeasy@...utronix.de,
 tglx@...utronix.de, rostedt@...dmis.org, linux-kernel@...r.kernel.org
Cc: hao3.li@...el.com, lili.li@...el.com, jianfeng.gao@...el.com,
 linux-rt-users@...r.kernel.org
Subject: Re: [PATCH 0/2] nbcon locking issue with v6.6.10-rt18 kernel

On 2024-01-23, Junxiao Chang <junxiao.chang@...el.com> wrote:
> There are two serial port devices in one Intel ADL hardware, one is
> 8250 lpss, another is 8250 dw. Multiple uart devices are enumerated as
> ttyS0, ttyS4, ttyS5,... With 6.6.10 rt18 kernel, booting hangs in
> nbcon_release if console is enabled by appending
> "console=ttySx,115200n8" to kernel command line. According to nbcon
> author John's suggestion, lock flag is moved from console structure to
> uart_port. Another patch is to add uart_is_nbcon checking in
> nbcon_release.

Isn't the real issue that the console pointer is copied to device that
are not consoles? I am wondering why that is. Is it possible to
dynamically switch the console index during runtime? If not, I think a
proper fix would be to only assign @cons if it actually registered as a
console. This would also simplify the uart_console() macro.

It is critical that a struct console is not shared by multiple
devices. I do not like the idea (or see the point) of having non-console
devices store a struct console pointer that is registered with another
device.

I will take a closer look at that.

John