[PATCH net-next v2 0/2] Allow disabling pause frames on panic

[PATCH net-next v2 0/2] Allow disabling pause frames on panic

[Florian Fainelli]

This patch set allows disabling pause frame generation upon encountering
a kernel panic. This has proven to be helpful in lab environments where
devices are still being worked on, will panic for various reasons, and
will occasionally take down the entire Ethernet switch they are attached
to.

Changes in v2:

- introduce a dedicated callback that runs in panic context

Florian Fainelli (2):
  net: ethernet: Allow disabling pause on panic
  net: bcmgenet: Add support for set_pauseparam_panic

 Documentation/ABI/testing/sysfs-class-net     | 16 ++++
 .../net/ethernet/broadcom/genet/bcmgenet.c    |  8 ++
 .../net/ethernet/broadcom/genet/bcmgenet.h    |  1 +
 drivers/net/ethernet/broadcom/genet/bcmmii.c  | 10 +++
 include/linux/ethtool.h                       |  3 +
 include/linux/netdevice.h                     |  1 +
 net/core/net-sysfs.c                          | 34 ++++++++
 net/ethernet/Makefile                         |  3 +-
 net/ethernet/pause_panic.c                    | 81 +++++++++++++++++++
 9 files changed, 156 insertions(+), 1 deletion(-)
 create mode 100644 net/ethernet/pause_panic.c

-- 
2.34.1

[PATCH net-next v2 1/2] net: ethernet: Allow disabling pause on panic

[Florian Fainelli]

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.

Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
---
 Documentation/ABI/testing/sysfs-class-net | 16 +++++
 include/linux/ethtool.h                   |  3 +
 include/linux/netdevice.h                 |  1 +
 net/core/net-sysfs.c                      | 34 ++++++++++
 net/ethernet/Makefile                     |  3 +-
 net/ethernet/pause_panic.c                | 81 +++++++++++++++++++++++
 6 files changed, 137 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..f762ce439203 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:	netdev@vger.kernel.org
+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  threaded mode disabled for this dev
+		1  threaded mode enabled for this dev
+		== ==================================
diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index c2d8b4ec62eb..e014d0f2a5ac 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -956,6 +956,8 @@ struct kernel_ethtool_ts_info {
  * @get_pauseparam: Report pause parameters
  * @set_pauseparam: Set pause parameters.  Returns a negative error code
  *	or zero.
+ * @set_pauseparam_panic: Set pause parameters while in a panic context. This
+ *	call is not allowed to sleep. Returns a negative error code or zero.
  * @self_test: Run specified self-tests
  * @get_strings: Return a set of strings that describe the requested objects
  * @set_phys_id: Identify the physical devices, e.g. by flashing an LED
@@ -1170,6 +1172,7 @@ struct ethtool_ops {
 				  struct ethtool_pauseparam*);
 	int	(*set_pauseparam)(struct net_device *,
 				  struct ethtool_pauseparam*);
+	void	(*set_pauseparam_panic)(struct net_device *);
 	void	(*self_test)(struct net_device *, struct ethtool_test *, u64 *);
 	void	(*get_strings)(struct net_device *, u32 stringset, u8 *);
 	int	(*set_phys_id)(struct net_device *, enum ethtool_phys_id_state);
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;
 
 	/* priv_flags_slow, ungrouped to save space */
 	unsigned long		see_all_hwtstamp_requests:1;
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index ca878525ad7c..c01dc3e200d8 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -770,6 +770,39 @@ static ssize_t threaded_store(struct device *dev,
 }
 static DEVICE_ATTR_RW(threaded);
 
+static ssize_t disable_pause_on_panic_show(struct device *dev,
+					    struct device_attribute *attr,
+					    char *buf)
+{
+	struct net_device *ndev = to_net_dev(dev);
+	ssize_t ret = -EINVAL;
+
+	rcu_read_lock();
+	if (dev_isalive(ndev))
+		ret = sysfs_emit(buf, fmt_dec, READ_ONCE(ndev->disable_pause_on_panic));
+	rcu_read_unlock();
+
+	return ret;
+}
+
+static int modify_disable_pause_on_panic(struct net_device *dev, unsigned long val)
+{
+	if (val != 0 && val != 1)
+		return -EINVAL;
+
+	WRITE_ONCE(dev->disable_pause_on_panic, val);
+
+	return 0;
+}
+
+static ssize_t disable_pause_on_panic_store(struct device *dev,
+					     struct device_attribute *attr,
+					     const char *buf, size_t len)
+{
+	return netdev_store(dev, attr, buf, len, modify_disable_pause_on_panic);
+}
+static DEVICE_ATTR_RW(disable_pause_on_panic);
+
 static struct attribute *net_class_attrs[] __ro_after_init = {
 	&dev_attr_netdev_group.attr,
 	&dev_attr_type.attr,
@@ -800,6 +833,7 @@ static struct attribute *net_class_attrs[] __ro_after_init = {
 	&dev_attr_carrier_up_count.attr,
 	&dev_attr_carrier_down_count.attr,
 	&dev_attr_threaded.attr,
+	&dev_attr_disable_pause_on_panic.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(net_class);
diff --git a/net/ethernet/Makefile b/net/ethernet/Makefile
index e03eff94e0db..9b1f3ff8695a 100644
--- a/net/ethernet/Makefile
+++ b/net/ethernet/Makefile
@@ -3,4 +3,5 @@
 # Makefile for the Linux Ethernet layer.
 #
 
-obj-y					+= eth.o
+obj-y					+= eth.o \
+					   pause_panic.o
diff --git a/net/ethernet/pause_panic.c b/net/ethernet/pause_panic.c
new file mode 100644
index 000000000000..8ef61eb768a0
--- /dev/null
+++ b/net/ethernet/pause_panic.c
@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Ethernet pause disable on panic handler
+ *
+ * This module provides per-device control via sysfs to disable Ethernet flow
+ * control (pause frames) on individual Ethernet devices when the kernel panics.
+ * Each device can be configured via /sys/class/net/<device>/disable_pause_on_panic.
+ */
+
+#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>
+
+/*
+ * 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.
+	 */
+	ops->set_pauseparam_panic(dev);
+}
+
+/*
+ * Panic notifier to disable pause frames on all Ethernet devices.
+ * Called in atomic context during kernel panic.
+ */
+static int eth_pause_panic_handler(struct notifier_block *this,
+					unsigned long event, void *ptr)
+{
+	struct net_device *dev;
+
+	/*
+	 * Iterate over all network devices in the init namespace.
+	 * In panic context, we cannot acquire locks that might sleep,
+	 * so we use RCU iteration.
+	 * Each device will check its own disable_pause_on_panic flag.
+	 */
+	rcu_read_lock();
+	for_each_netdev_rcu(&init_net, dev) {
+		/* Reference count might not be available in panic */
+		if (!dev)
+			continue;
+
+		disable_pause_on_device(dev);
+	}
+	rcu_read_unlock();
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block eth_pause_panic_notifier = {
+	.notifier_call = eth_pause_panic_handler,
+	.priority = INT_MAX, /* Run as late as possible */
+};
+
+static int __init eth_pause_panic_init(void)
+{
+	/* Register panic notifier */
+	atomic_notifier_chain_register(&panic_notifier_list,
+				       &eth_pause_panic_notifier);
+
+	return 0;
+}
+device_initcall(eth_pause_panic_init);
-- 
2.34.1

[PATCH net-next v2 2/2] net: bcmgenet: Add support for set_pauseparam_panic

[Florian Fainelli]

Avoid making sleeping calls that would in not being able to complete the
MMIO writes ignoring pause frame reception and generation at the
Ethernet MAC controller level.

Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
---
 drivers/net/ethernet/broadcom/genet/bcmgenet.c |  8 ++++++++
 drivers/net/ethernet/broadcom/genet/bcmgenet.h |  1 +
 drivers/net/ethernet/broadcom/genet/bcmmii.c   | 10 ++++++++++
 3 files changed, 19 insertions(+)

diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
index d99ef92feb82..323bf119c2af 100644
--- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
+++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
@@ -966,6 +966,13 @@ static int bcmgenet_set_pauseparam(struct net_device *dev,
 	return 0;
 }
 
+static void bcmgenet_set_pauseparam_panic(struct net_device *dev)
+{
+	struct bcmgenet_priv *priv = netdev_priv(dev);
+
+	bcmgenet_set_pause_panic(priv);
+}
+
 /* standard ethtool support functions. */
 enum bcmgenet_stat_type {
 	BCMGENET_STAT_RTNL = -1,
@@ -1702,6 +1709,7 @@ static const struct ethtool_ops bcmgenet_ethtool_ops = {
 	.set_rxnfc		= bcmgenet_set_rxnfc,
 	.get_pauseparam		= bcmgenet_get_pauseparam,
 	.set_pauseparam		= bcmgenet_set_pauseparam,
+	.set_pauseparam_panic	= bcmgenet_set_pauseparam_panic,
 };
 
 /* Power down the unimac, based on mode. */
diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.h b/drivers/net/ethernet/broadcom/genet/bcmgenet.h
index 5ec3979779ec..faf0d2406e9a 100644
--- a/drivers/net/ethernet/broadcom/genet/bcmgenet.h
+++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.h
@@ -738,6 +738,7 @@ int bcmgenet_mii_config(struct net_device *dev, bool init);
 int bcmgenet_mii_probe(struct net_device *dev);
 void bcmgenet_mii_exit(struct net_device *dev);
 void bcmgenet_phy_pause_set(struct net_device *dev, bool rx, bool tx);
+void bcmgenet_set_pause_panic(struct bcmgenet_priv *priv);
 void bcmgenet_phy_power_set(struct net_device *dev, bool enable);
 void bcmgenet_mii_setup(struct net_device *dev);
 
diff --git a/drivers/net/ethernet/broadcom/genet/bcmmii.c b/drivers/net/ethernet/broadcom/genet/bcmmii.c
index 38f854b94a79..a9a1d06032fa 100644
--- a/drivers/net/ethernet/broadcom/genet/bcmmii.c
+++ b/drivers/net/ethernet/broadcom/genet/bcmmii.c
@@ -147,6 +147,16 @@ void bcmgenet_phy_pause_set(struct net_device *dev, bool rx, bool tx)
 	mutex_unlock(&phydev->lock);
 }
 
+void bcmgenet_set_pause_panic(struct bcmgenet_priv *priv)
+{
+	u32 reg;
+
+	/* Disable pause frame generation and reception */
+	reg = bcmgenet_umac_readl(priv, UMAC_CMD);
+	reg |= CMD_RX_PAUSE_IGNORE | CMD_TX_PAUSE_IGNORE;
+	bcmgenet_umac_writel(priv, reg, UMAC_CMD);
+}
+
 void bcmgenet_phy_power_set(struct net_device *dev, bool enable)
 {
 	struct bcmgenet_priv *priv = netdev_priv(dev);
-- 
2.34.1

Re: [PATCH net-next v2 1/2] net: ethernet: Allow disabling pause on panic

[Kuniyuki Iwashima]

On Tue, Nov 4, 2025 at 2:13 PM Florian Fainelli
<florian.fainelli@broadcom.com> 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.
>
> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
> ---
>  Documentation/ABI/testing/sysfs-class-net | 16 +++++
>  include/linux/ethtool.h                   |  3 +
>  include/linux/netdevice.h                 |  1 +
>  net/core/net-sysfs.c                      | 34 ++++++++++
>  net/ethernet/Makefile                     |  3 +-
>  net/ethernet/pause_panic.c                | 81 +++++++++++++++++++++++
>  6 files changed, 137 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..f762ce439203 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:       netdev@vger.kernel.org
> +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  threaded mode disabled for this dev
> +               1  threaded mode enabled for this dev

nit: These lines need to be updated.


> +               == ==================================
> diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
> index c2d8b4ec62eb..e014d0f2a5ac 100644
> --- a/include/linux/ethtool.h
> +++ b/include/linux/ethtool.h
> @@ -956,6 +956,8 @@ struct kernel_ethtool_ts_info {
>   * @get_pauseparam: Report pause parameters
>   * @set_pauseparam: Set pause parameters.  Returns a negative error code
>   *     or zero.
> + * @set_pauseparam_panic: Set pause parameters while in a panic context. This
> + *     call is not allowed to sleep. Returns a negative error code or zero.
>   * @self_test: Run specified self-tests
>   * @get_strings: Return a set of strings that describe the requested objects
>   * @set_phys_id: Identify the physical devices, e.g. by flashing an LED
> @@ -1170,6 +1172,7 @@ struct ethtool_ops {
>                                   struct ethtool_pauseparam*);
>         int     (*set_pauseparam)(struct net_device *,
>                                   struct ethtool_pauseparam*);
> +       void    (*set_pauseparam_panic)(struct net_device *);
>         void    (*self_test)(struct net_device *, struct ethtool_test *, u64 *);
>         void    (*get_strings)(struct net_device *, u32 stringset, u8 *);
>         int     (*set_phys_id)(struct net_device *, enum ethtool_phys_id_state);
> 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;
>
>         /* priv_flags_slow, ungrouped to save space */
>         unsigned long           see_all_hwtstamp_requests:1;
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index ca878525ad7c..c01dc3e200d8 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -770,6 +770,39 @@ static ssize_t threaded_store(struct device *dev,
>  }
>  static DEVICE_ATTR_RW(threaded);
>
> +static ssize_t disable_pause_on_panic_show(struct device *dev,
> +                                           struct device_attribute *attr,
> +                                           char *buf)
> +{
> +       struct net_device *ndev = to_net_dev(dev);
> +       ssize_t ret = -EINVAL;
> +
> +       rcu_read_lock();
> +       if (dev_isalive(ndev))
> +               ret = sysfs_emit(buf, fmt_dec, READ_ONCE(ndev->disable_pause_on_panic));
> +       rcu_read_unlock();
> +
> +       return ret;
> +}
> +
> +static int modify_disable_pause_on_panic(struct net_device *dev, unsigned long val)
> +{
> +       if (val != 0 && val != 1)
> +               return -EINVAL;

Should we validate !ops->set_pauseparam_panic here
rather than disable_pause_on_device() ?

ops = dev->ethtool_ops;
if (!ops || !ops->set_pauseparam_panic)
    return -EOPNOTSUPP;


> +
> +       WRITE_ONCE(dev->disable_pause_on_panic, val);
> +
> +       return 0;
> +}
> +
> +static ssize_t disable_pause_on_panic_store(struct device *dev,
> +                                            struct device_attribute *attr,
> +                                            const char *buf, size_t len)
> +{
> +       return netdev_store(dev, attr, buf, len, modify_disable_pause_on_panic);
> +}
> +static DEVICE_ATTR_RW(disable_pause_on_panic);
> +
>  static struct attribute *net_class_attrs[] __ro_after_init = {
>         &dev_attr_netdev_group.attr,
>         &dev_attr_type.attr,
> @@ -800,6 +833,7 @@ static struct attribute *net_class_attrs[] __ro_after_init = {
>         &dev_attr_carrier_up_count.attr,
>         &dev_attr_carrier_down_count.attr,
>         &dev_attr_threaded.attr,
> +       &dev_attr_disable_pause_on_panic.attr,
>         NULL,
>  };
>  ATTRIBUTE_GROUPS(net_class);
> diff --git a/net/ethernet/Makefile b/net/ethernet/Makefile
> index e03eff94e0db..9b1f3ff8695a 100644
> --- a/net/ethernet/Makefile
> +++ b/net/ethernet/Makefile
> @@ -3,4 +3,5 @@
>  # Makefile for the Linux Ethernet layer.
>  #
>
> -obj-y                                  += eth.o
> +obj-y                                  += eth.o \
> +                                          pause_panic.o
> diff --git a/net/ethernet/pause_panic.c b/net/ethernet/pause_panic.c
> new file mode 100644
> index 000000000000..8ef61eb768a0
> --- /dev/null
> +++ b/net/ethernet/pause_panic.c
> @@ -0,0 +1,81 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Ethernet pause disable on panic handler
> + *
> + * This module provides per-device control via sysfs to disable Ethernet flow
> + * control (pause frames) on individual Ethernet devices when the kernel panics.
> + * Each device can be configured via /sys/class/net/<device>/disable_pause_on_panic.
> + */
> +
> +#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>
> +
> +/*
> + * 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.
> +        */
> +       ops->set_pauseparam_panic(dev);
> +}
> +
> +/*
> + * Panic notifier to disable pause frames on all Ethernet devices.
> + * Called in atomic context during kernel panic.
> + */
> +static int eth_pause_panic_handler(struct notifier_block *this,
> +                                       unsigned long event, void *ptr)
> +{
> +       struct net_device *dev;
> +
> +       /*
> +        * Iterate over all network devices in the init namespace.
> +        * In panic context, we cannot acquire locks that might sleep,
> +        * so we use RCU iteration.
> +        * Each device will check its own disable_pause_on_panic flag.
> +        */
> +       rcu_read_lock();
> +       for_each_netdev_rcu(&init_net, dev) {
> +               /* Reference count might not be available in panic */
> +               if (!dev)
> +                       continue;

This seems unnecessary unless while() + next_net_device_rcu()
is used instead of for_each_netdev_rcu().

Or are we assuming that something could overwrite NULL to
dev->dev_list.next and panic ?


> +
> +               disable_pause_on_device(dev);
> +       }
> +       rcu_read_unlock();
> +
> +       return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block eth_pause_panic_notifier = {
> +       .notifier_call = eth_pause_panic_handler,
> +       .priority = INT_MAX, /* Run as late as possible */
> +};
> +
> +static int __init eth_pause_panic_init(void)
> +{
> +       /* Register panic notifier */
> +       atomic_notifier_chain_register(&panic_notifier_list,
> +                                      &eth_pause_panic_notifier);
> +
> +       return 0;
> +}
> +device_initcall(eth_pause_panic_init);
> --
> 2.34.1
>

Re: [PATCH net-next v2 0/2] Allow disabling pause frames on panic

[Jakub Kicinski]

On Tue,  4 Nov 2025 14:13:46 -0800 Florian Fainelli wrote:
> This patch set allows disabling pause frame generation upon encountering
> a kernel panic. This has proven to be helpful in lab environments where
> devices are still being worked on, will panic for various reasons, and
> will occasionally take down the entire Ethernet switch they are attached to.

FWIW this still feels like a hack to work around having broken switches
to me :( Not sure how to stomach having a sysfs knob for every netdev on
the planet for one lab with cheap switches..

If anyone else has similar problems please speak up?

Re: [PATCH net-next v2 0/2] Allow disabling pause frames on panic

[Florian Fainelli]

On 11/4/25 15:57, Jakub Kicinski wrote:
> On Tue,  4 Nov 2025 14:13:46 -0800 Florian Fainelli wrote:
>> This patch set allows disabling pause frame generation upon encountering
>> a kernel panic. This has proven to be helpful in lab environments where
>> devices are still being worked on, will panic for various reasons, and
>> will occasionally take down the entire Ethernet switch they are attached to.
> 
> FWIW this still feels like a hack to work around having broken switches
> to me :( Not sure how to stomach having a sysfs knob for every netdev on
> the planet for one lab with cheap switches..

That's understandable, we have seen it with any sort of Ethernet 
adapter, GENET is the one that we have the most deployed, but we have 
seen that with Asix USB Ethernet dongles happen, which is why this made 
me look for a common solution, rather than a driver specific solution.

> 
> If anyone else has similar problems please speak up?


-- 
Florian

Re: [PATCH net-next v2 1/2] net: ethernet: Allow disabling pause on panic

[Florian Fainelli]

On 11/4/25 14:44, Kuniyuki Iwashima wrote:
> On Tue, Nov 4, 2025 at 2:13 PM Florian Fainelli
> <florian.fainelli@broadcom.com> 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.
>>
>> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
>> ---
>>   Documentation/ABI/testing/sysfs-class-net | 16 +++++
>>   include/linux/ethtool.h                   |  3 +
>>   include/linux/netdevice.h                 |  1 +
>>   net/core/net-sysfs.c                      | 34 ++++++++++
>>   net/ethernet/Makefile                     |  3 +-
>>   net/ethernet/pause_panic.c                | 81 +++++++++++++++++++++++
>>   6 files changed, 137 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..f762ce439203 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:       netdev@vger.kernel.org
>> +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  threaded mode disabled for this dev
>> +               1  threaded mode enabled for this dev
> 
> nit: These lines need to be updated.
> 
> 
>> +               == ==================================
>> diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
>> index c2d8b4ec62eb..e014d0f2a5ac 100644
>> --- a/include/linux/ethtool.h
>> +++ b/include/linux/ethtool.h
>> @@ -956,6 +956,8 @@ struct kernel_ethtool_ts_info {
>>    * @get_pauseparam: Report pause parameters
>>    * @set_pauseparam: Set pause parameters.  Returns a negative error code
>>    *     or zero.
>> + * @set_pauseparam_panic: Set pause parameters while in a panic context. This
>> + *     call is not allowed to sleep. Returns a negative error code or zero.
>>    * @self_test: Run specified self-tests
>>    * @get_strings: Return a set of strings that describe the requested objects
>>    * @set_phys_id: Identify the physical devices, e.g. by flashing an LED
>> @@ -1170,6 +1172,7 @@ struct ethtool_ops {
>>                                    struct ethtool_pauseparam*);
>>          int     (*set_pauseparam)(struct net_device *,
>>                                    struct ethtool_pauseparam*);
>> +       void    (*set_pauseparam_panic)(struct net_device *);
>>          void    (*self_test)(struct net_device *, struct ethtool_test *, u64 *);
>>          void    (*get_strings)(struct net_device *, u32 stringset, u8 *);
>>          int     (*set_phys_id)(struct net_device *, enum ethtool_phys_id_state);
>> 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;
>>
>>          /* priv_flags_slow, ungrouped to save space */
>>          unsigned long           see_all_hwtstamp_requests:1;
>> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
>> index ca878525ad7c..c01dc3e200d8 100644
>> --- a/net/core/net-sysfs.c
>> +++ b/net/core/net-sysfs.c
>> @@ -770,6 +770,39 @@ static ssize_t threaded_store(struct device *dev,
>>   }
>>   static DEVICE_ATTR_RW(threaded);
>>
>> +static ssize_t disable_pause_on_panic_show(struct device *dev,
>> +                                           struct device_attribute *attr,
>> +                                           char *buf)
>> +{
>> +       struct net_device *ndev = to_net_dev(dev);
>> +       ssize_t ret = -EINVAL;
>> +
>> +       rcu_read_lock();
>> +       if (dev_isalive(ndev))
>> +               ret = sysfs_emit(buf, fmt_dec, READ_ONCE(ndev->disable_pause_on_panic));
>> +       rcu_read_unlock();
>> +
>> +       return ret;
>> +}
>> +
>> +static int modify_disable_pause_on_panic(struct net_device *dev, unsigned long val)
>> +{
>> +       if (val != 0 && val != 1)
>> +               return -EINVAL;
> 
> Should we validate !ops->set_pauseparam_panic here
> rather than disable_pause_on_device() ?

Yes we should certainly do it here to give an early warning to users 
whether this will work or not. To keep things simple however, we would 
still need to check set_pauseparam_panic in the panic handler, otherwise 
we would have to construct a list of network devices that do support the 
operation and use that.

> 
> ops = dev->ethtool_ops;
> if (!ops || !ops->set_pauseparam_panic)
>      return -EOPNOTSUPP;
> 
> 
>> +
>> +       WRITE_ONCE(dev->disable_pause_on_panic, val);
>> +
>> +       return 0;
>> +}
>> +
>> +static ssize_t disable_pause_on_panic_store(struct device *dev,
>> +                                            struct device_attribute *attr,
>> +                                            const char *buf, size_t len)
>> +{
>> +       return netdev_store(dev, attr, buf, len, modify_disable_pause_on_panic);
>> +}
>> +static DEVICE_ATTR_RW(disable_pause_on_panic);
>> +
>>   static struct attribute *net_class_attrs[] __ro_after_init = {
>>          &dev_attr_netdev_group.attr,
>>          &dev_attr_type.attr,
>> @@ -800,6 +833,7 @@ static struct attribute *net_class_attrs[] __ro_after_init = {
>>          &dev_attr_carrier_up_count.attr,
>>          &dev_attr_carrier_down_count.attr,
>>          &dev_attr_threaded.attr,
>> +       &dev_attr_disable_pause_on_panic.attr,
>>          NULL,
>>   };
>>   ATTRIBUTE_GROUPS(net_class);
>> diff --git a/net/ethernet/Makefile b/net/ethernet/Makefile
>> index e03eff94e0db..9b1f3ff8695a 100644
>> --- a/net/ethernet/Makefile
>> +++ b/net/ethernet/Makefile
>> @@ -3,4 +3,5 @@
>>   # Makefile for the Linux Ethernet layer.
>>   #
>>
>> -obj-y                                  += eth.o
>> +obj-y                                  += eth.o \
>> +                                          pause_panic.o
>> diff --git a/net/ethernet/pause_panic.c b/net/ethernet/pause_panic.c
>> new file mode 100644
>> index 000000000000..8ef61eb768a0
>> --- /dev/null
>> +++ b/net/ethernet/pause_panic.c
>> @@ -0,0 +1,81 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Ethernet pause disable on panic handler
>> + *
>> + * This module provides per-device control via sysfs to disable Ethernet flow
>> + * control (pause frames) on individual Ethernet devices when the kernel panics.
>> + * Each device can be configured via /sys/class/net/<device>/disable_pause_on_panic.
>> + */
>> +
>> +#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>
>> +
>> +/*
>> + * 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.
>> +        */
>> +       ops->set_pauseparam_panic(dev);
>> +}
>> +
>> +/*
>> + * Panic notifier to disable pause frames on all Ethernet devices.
>> + * Called in atomic context during kernel panic.
>> + */
>> +static int eth_pause_panic_handler(struct notifier_block *this,
>> +                                       unsigned long event, void *ptr)
>> +{
>> +       struct net_device *dev;
>> +
>> +       /*
>> +        * Iterate over all network devices in the init namespace.
>> +        * In panic context, we cannot acquire locks that might sleep,
>> +        * so we use RCU iteration.
>> +        * Each device will check its own disable_pause_on_panic flag.
>> +        */
>> +       rcu_read_lock();
>> +       for_each_netdev_rcu(&init_net, dev) {
>> +               /* Reference count might not be available in panic */
>> +               if (!dev)
>> +                       continue;
> 
> This seems unnecessary unless while() + next_net_device_rcu()
> is used instead of for_each_netdev_rcu().
> 
> Or are we assuming that something could overwrite NULL to
> dev->dev_list.next and panic ?

In panic context not much can happen by this point, so I presume we can 
just walk the list of network devices in the init space with no specific 
locking or protection of any sort.

Thanks for your review!
-- 
Florian