netdev - Re: [PATCH net-next v2 3/5] netconsole: convert to NBCON console infrastructure

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Message-ID: <aXKSDoi8Yue_Ghxj@horms.kernel.org>
Date: Thu, 22 Jan 2026 21:09:34 +0000
From: Simon Horman <horms@...nel.org>
To: Breno Leitao <leitao@...ian.org>
Cc: Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	pmladek@...e.com, john.ogness@...utronix.de,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, asantostc@...il.com, efault@....de,
	gustavold@...il.com, calvin@...nvd.org, jv@...sburgh.net,
	mpdesouza@...e.com, kernel-team@...a.com
Subject: Re: [PATCH net-next v2 3/5] netconsole: convert to NBCON console
 infrastructure

On Tue, Jan 20, 2026 at 08:23:49AM -0800, Breno Leitao wrote:
> Convert netconsole from the legacy console API to the NBCON framework.
> NBCON provides threaded printing which unblocks printk()s and flushes in
> a thread, decoupling network TX from printk() when netconsole is
> in use.
> 
> Since netconsole relies on the network stack which cannot safely operate
> from all atomic contexts, mark both consoles with
> CON_NBCON_ATOMIC_UNSAFE. (See discussion in [1])
> 
> CON_NBCON_ATOMIC_UNSAFE restricts write_atomic() usage to emergency
> scenarios (panic) where regular messages are sent in threaded mode.
> 
> Implementation changes:
> - Unify write_ext_msg() and write_msg() into netconsole_write()
> - Add device_lock/device_unlock callbacks to manage target_list_lock
> - Use nbcon_enter_unsafe()/nbcon_exit_unsafe() around network
>   operations.
>   - If nbcon_enter_unsafe() fails, just return given netconsole lost
>     the ownership of the console.
> - Set write_thread and write_atomic callbacks (both use same function)
> 
> Link: https://lore.kernel.org/all/b2qps3uywhmjaym4mht2wpxul4yqtuuayeoq4iv4k3zf5wdgh3@tocu6c7mj4lt/ [1]
> Signed-off-by: Breno Leitao <leitao@...ian.org>
> ---
>  drivers/net/netconsole.c | 97 ++++++++++++++++++++++++++++++------------------
>  1 file changed, 60 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c

...

> +static void netconsole_device_lock(struct console *con __always_unused,
> +				   unsigned long *flags)
> +{
> +	spin_lock_irqsave(&target_list_lock, *flags);
> +}
> +
> +static void netconsole_device_unlock(struct console *con __always_unused,
> +				     unsigned long flags)
> +{
>  	spin_unlock_irqrestore(&target_list_lock, flags);
>  }
>  

Hi Breno,

I'm wondering if we could consider the following annotations,
as "suggested" by Sparse[1].

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index c5d7e97fe2a7..79e39a6c5343 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -1772,12 +1772,14 @@ static void netconsole_write_basic(struct console *con __always_unused,
 
 static void netconsole_device_lock(struct console *con __always_unused,
 				   unsigned long *flags)
+__acquires(&target_list_lock)
 {
 	spin_lock_irqsave(&target_list_lock, *flags);
 }
 
 static void netconsole_device_unlock(struct console *con __always_unused,
 				     unsigned long flags)
+__releases(&target_list_lock)
 {
 	spin_unlock_irqrestore(&target_list_lock, flags);
 }

[1] This particular commit of Sparse, from Al Viro's tree:
    https://git.kernel.org/pub/scm/linux/kernel/git/viro/sparse.git/commit/?id=2634e39bf02697a18fece057208150362c985992
    Which addresses this mess:
    https://lore.kernel.org/all/bf5b9a62-a120-421e-908d-1404c42e0b60@kernel.org/