Subject: Re: [PATCH net-next v3 1/2] net: ethernet: Allow disabling pause on panic

From: Jakub Kicinski <[email-masked]>
Date: Mon, 10 Nov 2025 17:10:36 -0800

On Thu,  6 Nov 2025 16:25:09 -0800 Florian Fainelli wrote:
> Development devices on a lab network might be subject to kernel panics
> and if they have pause frame generation enabled, once the kernel panics,
> the Ethernet controller stops being serviced. This can create a flood of
> pause frames that certain switches are unable to handle resulting a
> completle paralysis of the network because they broadcast to other
> stations on that same network segment.
> 
> To accomodate for such situation introduce a
> /sys/class/net/<device>/disable_pause_on_panic knob which will disable
> Ethernet pause frame generation upon kernel panic.
> 
> Note that device driver wishing to make use of that feature need to
> implement ethtool_ops::set_pauseparam_panic to specifically deal with
> that atomic context.

Some basic review comments below (no promises if addressing those will
make me for one feel any warmer towards the concept).

>  Documentation/ABI/testing/sysfs-class-net | 16 +++++
>  include/linux/ethtool.h                   |  3 +
>  include/linux/netdevice.h                 |  1 +
>  net/core/net-sysfs.c                      | 39 +++++++++++
>  net/ethernet/Makefile                     |  3 +-
>  net/ethernet/pause_panic.c                | 79 +++++++++++++++++++++++

panic.c or shutdown.c is probably a slightly better name,
more likely we'd add more code in that.

>  6 files changed, 140 insertions(+), 1 deletion(-)
>  create mode 100644 net/ethernet/pause_panic.c
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-net b/Documentation/ABI/testing/sysfs-class-net
> index ebf21beba846..da0e4e862aca 100644
> --- a/Documentation/ABI/testing/sysfs-class-net
> +++ b/Documentation/ABI/testing/sysfs-class-net
> @@ -352,3 +352,19 @@ Description:
>  		0  threaded mode disabled for this dev
>  		1  threaded mode enabled for this dev
>  		== ==================================
> +
> +What:		/sys/class/net/<iface>/disable_pause_on_panic
> +Date:		Nov 2025
> +KernelVersion:	6.20
> +Contact:	[email-masked]
> +Description:
> +		Boolean value to control whether to disable pause frame
> +		generation on panic. This is helpful in environments where
> +		the link partner may incorrect respond to pause frames (e.g.:
> +		improperly configured Ethernet switches)
> +
> +		Possible values:
> +		== =====================================================
> +		0  do not disable pause frame generation on kernel panic
> +		1  disable pause frame generation on kernel panic
> +		== =====================================================

please no sysfs for something as niche as this feature

> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index e808071dbb7d..2d4b07693745 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -2441,6 +2441,7 @@ struct net_device {
>  	bool			proto_down;
>  	bool			irq_affinity_auto;
>  	bool			rx_cpu_rmap_auto;
> +	bool			disable_pause_on_panic;

Warning: include/linux/netdevice.h:2567 struct member
'disable_pause_on_panic' not described in 'net_device'

>  	/* priv_flags_slow, ungrouped to save space */
>  	unsigned long		see_all_hwtstamp_requests:1;

> +#include <linux/kernel.h>
> +#include <linux/init.h>
> +#include <linux/panic_notifier.h>
> +#include <linux/netdevice.h>
> +#include <linux/ethtool.h>
> +#include <linux/notifier.h>
> +#include <linux/if_ether.h>
> +#include <net/net_namespace.h>

Alphabetical sort, please.

> +/*
> + * Disable pause/flow control on a single Ethernet device.
> + */
> +static void disable_pause_on_device(struct net_device *dev)
> +{
> +	const struct ethtool_ops *ops;
> +
> +	/* Only proceed if this device has the flag enabled */
> +	if (!READ_ONCE(dev->disable_pause_on_panic))
> +		return;
> +
> +	ops = dev->ethtool_ops;
> +	if (!ops || !ops->set_pauseparam_panic)
> +		return;
> +
> +	/*
> +	 * In panic context, we're in atomic context and cannot sleep.
> +	 */

single-line comment would do?

> +	ops->set_pauseparam_panic(dev);
> +}
-- 
pw-bot: cr