linux-kernel - Re: [PATCH printk v1 0/1] Allow unsafe ->write

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Message-ID: <844ispin6a.fsf@jogness.linutronix.de>
Date: Fri, 26 Sep 2025 11:27:49 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Breno Leitao <leitao@...ian.org>
Cc: Petr Mladek <pmladek@...e.com>, Sergey Senozhatsky
 <senozhatsky@...omium.org>, Steven Rostedt <rostedt@...dmis.org>, Mike
 Galbraith <efault@....de>, linux-kernel@...r.kernel.org, Greg
 Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH printk v1 0/1] Allow unsafe ->write_atomic() for panic

Hi Breno,

On 2025-09-17, Breno Leitao <leitao@...ian.org> wrote:
> Upon further consideration, it's worth noting that not all network
> drivers rely on irq-unsafe locks. In practice, only a subset of drivers
> use them, while most network drivers I'm familiar with maintain IRQ-safe
> TX paths.
>
> If we could determine the IRQ safety characteristics (IRQ-safe vs
> IRQ-unsafe TX) during netconsole registration, this would enable more
> optimized behavior: netconsole could register as CON_NBCON_ATOMIC_UNSAFE
> only when the underlying network adapter uses IRQ-unsafe locks. For
> adapters with IRQ-safe implementations, netconsole could safely utilize
> the ->write_atomic path without restrictions.

This is good to read. But note that if CON_NBCON_ATOMIC_UNSAFE is not
set, it is expected that ->write_atomic() will also function in NMI. So
being IRQ-safe may not be enough.

John Ogness