linux-kernel - Re: [PATCH 2/2] printk: nbcon: check uart port is nbcon or not in nbcon

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Date: Wed, 24 Jan 2024 11:03:39 +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 2/2] printk: nbcon: check uart port is nbcon or not in
 nbcon_release

On 2024-01-23, Junxiao Chang <junxiao.chang@...el.com> wrote:
> Try to release nbcon only if current uart port is nbcon, as it does
> in nbcon_acquire.

The release needs to undo what acquire did. Why should it have its own
checks that would cause it to _not_ undo what acquire did?

Keep in mind that an nbcon console could be unregistered while another
CPU is holding the nbcon lock. The port lock (and nbcon lock) are
protecting access to the hardware. They are not related to console
registration/unregistration.

John