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

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Message-ID: <aXNRR7dQHZ7bN2mS@gmail.com>
Date: Fri, 23 Jan 2026 02:48:47 -0800
From: Breno Leitao <leitao@...ian.org>
To: Simon Horman <horms@...nel.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

Hello Simon!

On Thu, Jan 22, 2026 at 09:09:34PM +0000, Simon Horman wrote:
> 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].

This is great. I hadn't realized that Al Viro's sparse tree includes this
additional check, which is really useful.

Are you using Al Viro's branch rather than the sparse mainline?

(I'm asking to see if I should also follow master and do the same, in
true padawan fashion)