[PATCH net v2 0/2] net: stmmac: Fix XSK crashes on stm32mp2

[PATCH net v2 0/2] net: stmmac: Fix XSK crashes on stm32mp2

[Kurt Kanzenbach]

Hi,

while looking at the TBS thingy [1], I've noticed kernel crashes. That
happens when opening or closing an AF_XDP/ZC socket while parallel Tx
traffic is going on.

So far, I see two issues:

 - Patch #1: stmmac_xdp_release() seems to have the teardown order wrong
 - Patch #2: stmmac_xdp_(en|dis)able_pool() does not stop the Tx queue
   at all

The kernel crashes can be reproduced instantly on the stm32mp2 like this:

 - Run iperf3
 - Run application which opens an AF_XDP/ZC socket

[1] - https://lore.kernel.org/all/20260812-stm32mp2_txtime-v1-1-f9e2462cc85d@linutronix.de/

Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
---
Changes in v2:
- Remove RFC. No comments.
- Link to v1: https://patch.msgid.link/20260915-stmmac_xsk_crashes-v1-0-e14553fcf553@linutronix.de

---
Kurt Kanzenbach (2):
      net: stmmac: Disable NAPI before stopping Tx queues in stmmac_xdp_release()
      net: stmmac: Stop Tx queue when (en|dis)abling XSK pools

 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c |  6 +++---
 drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c  | 14 ++++++++++++++
 2 files changed, 17 insertions(+), 3 deletions(-)
---
base-commit: aaaaf87ea99b8766c9a8aa0e71aa42e6bc8a5320
change-id: 20260914-stmmac_xsk_crashes-10a77f614ab5

Best regards,
--  
Kurt Kanzenbach <kurt@linutronix.de>

[PATCH net v2 1/2] net: stmmac: Disable NAPI before stopping Tx queues in stmmac_xdp_release()

[Kurt Kanzenbach]

Attaching an XDP program while Tx traffic is running results in kernel
crashes in stmmac_xmit() -> dwmac4_set_addr().

Loading an XDP program tears down and reallocates all DMA resources via
stmmac_xdp_release() and stmmac_xdp_open(). stmmac_xdp_release() stops
the Tx queues before disabling NAPI:

 stmmac_xdp_release:
   netif_tx_disable
   stmmac_disable_all_queues
   ...
   free_dma_desc_resources

A Tx NAPI poll may still be in flight at that point. stmmac_tx_clean()
takes the Tx queue lock, reaps completed descriptors and wakes the queue
again when it observes it stopped with enough descriptors available.
Nothing stops the queue afterwards, so the Tx path resumes while
free_dma_desc_resources() releases the descriptor rings underneath it.

On non-coherent platforms dma_free_coherent() tears down the vmalloc
mapping of the descriptors, so the subsequent stmmac_xmit() faults on an
unmapped address instead of corrupting memory silently.

Disable NAPI first and stop the Tx queues afterwards, which is the order
already used by __stmmac_release().

The issue can be easily reproduced by:

 1. Run iperf
 2. Run application which opens an AF_XDP/ZC socket

Assisted-by: Claude:claude-opus-5
Fixes: 77711683a504 ("net: stmmac: ensure tx function is not running in stmmac_xdp_release()")
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 9741f97fa37a..796817caf7af 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -7178,15 +7178,15 @@ void stmmac_xdp_release(struct net_device *dev)
 	struct stmmac_priv *priv = netdev_priv(dev);
 	u8 chan;
 
-	/* Ensure tx function is not running */
-	netif_tx_disable(dev);
-
 	/* Disable NAPI process */
 	stmmac_disable_all_queues(priv);
 
 	for (chan = 0; chan < priv->plat->tx_queues_to_use; chan++)
 		hrtimer_cancel(&priv->dma_conf.tx_queue[chan].txtimer);
 
+	/* Ensure tx function is not running */
+	netif_tx_disable(dev);
+
 	/* Free the IRQ lines */
 	stmmac_free_irq(dev, REQ_IRQ_ERR_ALL, 0);
 

-- 
2.47.3

Re: [PATCH net v2 1/2] net: stmmac: Disable NAPI before stopping Tx queues in stmmac_xdp_release()

[Maxime Chevallier]

Hi Kurt,

On 10/5/26 09:09, Kurt Kanzenbach wrote:
> Attaching an XDP program while Tx traffic is running results in kernel
> crashes in stmmac_xmit() -> dwmac4_set_addr().
> 
> Loading an XDP program tears down and reallocates all DMA resources via
> stmmac_xdp_release() and stmmac_xdp_open(). stmmac_xdp_release() stops
> the Tx queues before disabling NAPI:
> 
>  stmmac_xdp_release:
>    netif_tx_disable
>    stmmac_disable_all_queues
>    ...
>    free_dma_desc_resources
> 
> A Tx NAPI poll may still be in flight at that point. stmmac_tx_clean()
> takes the Tx queue lock, reaps completed descriptors and wakes the queue
> again when it observes it stopped with enough descriptors available.
> Nothing stops the queue afterwards, so the Tx path resumes while
> free_dma_desc_resources() releases the descriptor rings underneath it.
> 
> On non-coherent platforms dma_free_coherent() tears down the vmalloc
> mapping of the descriptors, so the subsequent stmmac_xmit() faults on an
> unmapped address instead of corrupting memory silently.
> 
> Disable NAPI first and stop the Tx queues afterwards, which is the order
> already used by __stmmac_release().
> 
> The issue can be easily reproduced by:
> 
>  1. Run iperf
>  2. Run application which opens an AF_XDP/ZC socket
> 
> Assisted-by: Claude:claude-opus-5
> Fixes: 77711683a504 ("net: stmmac: ensure tx function is not running in stmmac_xdp_release()")
> Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>

This now matches the non-xdp case, great :)

Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>

Maxime

> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index 9741f97fa37a..796817caf7af 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -7178,15 +7178,15 @@ void stmmac_xdp_release(struct net_device *dev)
>  	struct stmmac_priv *priv = netdev_priv(dev);
>  	u8 chan;
>  
> -	/* Ensure tx function is not running */
> -	netif_tx_disable(dev);
> -
>  	/* Disable NAPI process */
>  	stmmac_disable_all_queues(priv);
>  
>  	for (chan = 0; chan < priv->plat->tx_queues_to_use; chan++)
>  		hrtimer_cancel(&priv->dma_conf.tx_queue[chan].txtimer);
>  
> +	/* Ensure tx function is not running */
> +	netif_tx_disable(dev);
> +
>  	/* Free the IRQ lines */
>  	stmmac_free_irq(dev, REQ_IRQ_ERR_ALL, 0);
>  
> 

Re: [PATCH net v2 1/2] net: stmmac: Disable NAPI before stopping Tx queues in stmmac_xdp_release()

[Kurt Kanzenbach]

[-- Attachment #1: Type: text/plain, Size: 1868 bytes --]

Hi Maxime,

On Mon Oct 05 2026, Maxime Chevallier wrote:
> On 10/5/26 09:09, Kurt Kanzenbach wrote:
>> Attaching an XDP program while Tx traffic is running results in kernel
>> crashes in stmmac_xmit() -> dwmac4_set_addr().
>> 
>> Loading an XDP program tears down and reallocates all DMA resources via
>> stmmac_xdp_release() and stmmac_xdp_open(). stmmac_xdp_release() stops
>> the Tx queues before disabling NAPI:
>> 
>>  stmmac_xdp_release:
>>    netif_tx_disable
>>    stmmac_disable_all_queues
>>    ...
>>    free_dma_desc_resources
>> 
>> A Tx NAPI poll may still be in flight at that point. stmmac_tx_clean()
>> takes the Tx queue lock, reaps completed descriptors and wakes the queue
>> again when it observes it stopped with enough descriptors available.
>> Nothing stops the queue afterwards, so the Tx path resumes while
>> free_dma_desc_resources() releases the descriptor rings underneath it.
>> 
>> On non-coherent platforms dma_free_coherent() tears down the vmalloc
>> mapping of the descriptors, so the subsequent stmmac_xmit() faults on an
>> unmapped address instead of corrupting memory silently.
>> 
>> Disable NAPI first and stop the Tx queues afterwards, which is the order
>> already used by __stmmac_release().
>> 
>> The issue can be easily reproduced by:
>> 
>>  1. Run iperf
>>  2. Run application which opens an AF_XDP/ZC socket
>> 
>> Assisted-by: Claude:claude-opus-5
>> Fixes: 77711683a504 ("net: stmmac: ensure tx function is not running in stmmac_xdp_release()")
>> Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
>
> This now matches the non-xdp case, great :)

Thanks for the review! Yes, it does match now. We could also collapse
the common teardown code between __stmmac_release() and
stmmac_xdp_release() into a helper function now and reduce code
duplication.

Thanks,
Kurt

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Re: [PATCH net v2 1/2] net: stmmac: Disable NAPI before stopping Tx queues in stmmac_xdp_release()

[Nicolai Buchwitz]

Hi Kurt

On 5.10.2026 09:09, Kurt Kanzenbach wrote:
> Attaching an XDP program while Tx traffic is running results in kernel
> crashes in stmmac_xmit() -> dwmac4_set_addr().
> 
> Loading an XDP program tears down and reallocates all DMA resources via
> stmmac_xdp_release() and stmmac_xdp_open(). stmmac_xdp_release() stops
> the Tx queues before disabling NAPI:
> 
>  stmmac_xdp_release:
>    netif_tx_disable
>    stmmac_disable_all_queues
>    ...
>    free_dma_desc_resources
> 
> A Tx NAPI poll may still be in flight at that point. stmmac_tx_clean()
> takes the Tx queue lock, reaps completed descriptors and wakes the 
> queue
> again when it observes it stopped with enough descriptors available.
> Nothing stops the queue afterwards, so the Tx path resumes while
> free_dma_desc_resources() releases the descriptor rings underneath it.
> 
> On non-coherent platforms dma_free_coherent() tears down the vmalloc
> mapping of the descriptors, so the subsequent stmmac_xmit() faults on 
> an
> unmapped address instead of corrupting memory silently.
> 
> Disable NAPI first and stop the Tx queues afterwards, which is the 
> order
> already used by __stmmac_release().
> 
> The issue can be easily reproduced by:
> 
>  1. Run iperf
>  2. Run application which opens an AF_XDP/ZC socket
> 
> Assisted-by: Claude:claude-opus-5
> Fixes: 77711683a504 ("net: stmmac: ensure tx function is not running in 
> stmmac_xdp_release()")
> Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>

> [...]

Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>
Tested-by: Nicolai Buchwitz <nb@tipi-net.de> # stm32mp215

Thanks,
Nicolai

[PATCH net v2 2/2] net: stmmac: Stop Tx queue when (en|dis)abling XSK pools

[Kurt Kanzenbach]

When enabling or disabling XSK pools in parallel to Tx traffic, kernel
crashes occur. For VLAN tagged frames that happens in stmmac_xmit() ->
dwmac4_set_vlan_tag() and for normal frames in stmmac_xmit() ->
dwmac4_set_addr(). Both of these functions access the Tx DMA descriptors.

The XDP pool (en|dis)ablement frees and reallocates the Tx DMA resources:

 stmmac_disable_tx_queue:
   __free_dma_tx_desc_resources

 stmmac_enable_tx_queue:
   __alloc_dma_tx_desc_resources
   __init_dma_tx_desc_rings

NAPI is disabled during that allocation window, but the Tx queue is not
stopped. Therefore, add the stopping of the Tx queue during the enabling
and disabling of XSK pools. Update trans_start when stopping the queue
to avoid spurious watchdog timeouts.

The issue can be easily reproduced by:

 1. Run iperf
 2. Run application which opens an AF_XDP/ZC socket

Fixes: 132c32ee5bc0 ("net: stmmac: Add TX via XDP zero-copy socket")
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
index d7e4db7224b0..883bd3fe8089 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
@@ -6,6 +6,16 @@
 #include "stmmac.h"
 #include "stmmac_xdp.h"
 
+static void stmmac_xdp_stop_tx_queue(struct stmmac_priv *priv, u16 queue)
+{
+	struct netdev_queue *nq = netdev_get_tx_queue(priv->dev, queue);
+
+	__netif_tx_lock_bh(nq);
+	txq_trans_cond_update(nq);
+	netif_tx_stop_queue(nq);
+	__netif_tx_unlock_bh(nq);
+}
+
 static int stmmac_xdp_enable_pool(struct stmmac_priv *priv,
 				  struct xsk_buff_pool *pool, u16 queue)
 {
@@ -36,6 +46,7 @@ static int stmmac_xdp_enable_pool(struct stmmac_priv *priv,
 	if (need_update) {
 		napi_disable(&ch->rx_napi);
 		napi_disable(&ch->tx_napi);
+		stmmac_xdp_stop_tx_queue(priv, queue);
 		stmmac_disable_rx_queue(priv, queue);
 		stmmac_disable_tx_queue(priv, queue);
 	}
@@ -46,6 +57,7 @@ static int stmmac_xdp_enable_pool(struct stmmac_priv *priv,
 		stmmac_enable_rx_queue(priv, queue);
 		stmmac_enable_tx_queue(priv, queue);
 		napi_enable(&ch->rxtx_napi);
+		netif_tx_wake_queue(netdev_get_tx_queue(priv->dev, queue));
 
 		err = stmmac_xsk_wakeup(priv->dev, queue, XDP_WAKEUP_RX);
 		if (err)
@@ -73,6 +85,7 @@ static int stmmac_xdp_disable_pool(struct stmmac_priv *priv, u16 queue)
 
 	if (need_update) {
 		napi_disable(&ch->rxtx_napi);
+		stmmac_xdp_stop_tx_queue(priv, queue);
 		stmmac_disable_rx_queue(priv, queue);
 		stmmac_disable_tx_queue(priv, queue);
 		synchronize_rcu();
@@ -87,6 +100,7 @@ static int stmmac_xdp_disable_pool(struct stmmac_priv *priv, u16 queue)
 		stmmac_enable_tx_queue(priv, queue);
 		napi_enable(&ch->rx_napi);
 		napi_enable(&ch->tx_napi);
+		netif_tx_wake_queue(netdev_get_tx_queue(priv->dev, queue));
 	}
 
 	return 0;

-- 
2.47.3

Re: [PATCH net v2 2/2] net: stmmac: Stop Tx queue when (en|dis)abling XSK pools

[Nicolai Buchwitz]

Hi Kurt

On 5.10.2026 09:09, Kurt Kanzenbach wrote:
> When enabling or disabling XSK pools in parallel to Tx traffic, kernel
> crashes occur. For VLAN tagged frames that happens in stmmac_xmit() ->
> dwmac4_set_vlan_tag() and for normal frames in stmmac_xmit() ->
> dwmac4_set_addr(). Both of these functions access the Tx DMA 
> descriptors.
> 
> The XDP pool (en|dis)ablement frees and reallocates the Tx DMA 
> resources:
> 
>  stmmac_disable_tx_queue:
>    __free_dma_tx_desc_resources
> 
>  stmmac_enable_tx_queue:
>    __alloc_dma_tx_desc_resources
>    __init_dma_tx_desc_rings
> 
> NAPI is disabled during that allocation window, but the Tx queue is not
> stopped. Therefore, add the stopping of the Tx queue during the 
> enabling
> and disabling of XSK pools. Update trans_start when stopping the queue
> to avoid spurious watchdog timeouts.
> 
> The issue can be easily reproduced by:
> 
>  1. Run iperf
>  2. Run application which opens an AF_XDP/ZC socket
> 
> Fixes: 132c32ee5bc0 ("net: stmmac: Add TX via XDP zero-copy socket")
> Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c 
> b/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
> index d7e4db7224b0..883bd3fe8089 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
> @@ -6,6 +6,16 @@
>  #include "stmmac.h"
>  #include "stmmac_xdp.h"
> 
> +static void stmmac_xdp_stop_tx_queue(struct stmmac_priv *priv, u16 
> queue)
> +{
> +	struct netdev_queue *nq = netdev_get_tx_queue(priv->dev, queue);
> +
> +	__netif_tx_lock_bh(nq);
> +	txq_trans_cond_update(nq);
> +	netif_tx_stop_queue(nq);
> +	__netif_tx_unlock_bh(nq);
> +}
> +
>  static int stmmac_xdp_enable_pool(struct stmmac_priv *priv,
>  				  struct xsk_buff_pool *pool, u16 queue)
>  {
> @@ -36,6 +46,7 @@ static int stmmac_xdp_enable_pool(struct stmmac_priv 
> *priv,
>  	if (need_update) {
>  		napi_disable(&ch->rx_napi);
>  		napi_disable(&ch->tx_napi);
> +		stmmac_xdp_stop_tx_queue(priv, queue);

Unfortunately XDP_TX and ndo_xdp_xmit() ignore the stopped queue and 
still
hit the freed ring. I can reproduce this on STM32MP215 with a veth 
redirect
into the port while toggling the pool:

   pc : dwmac4_set_addr+0x8/0x18
   lr : stmmac_xdp_xmit_xdpf+0x1d0/0x3f0
    stmmac_xdp_xmit+0xe4/0x1a8
    bq_xmit_all+0xa0/0x208
    __dev_flush+0x60/0xc0
    xdp_do_flush+0x134/0x198
    veth_poll+0x258/0x340

Both go through stmmac_xdp_xmit_xdpf() with the queue lock held, so this
fixes it for me:

--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ static int stmmac_xdp_xmit_xdpf(struct stmmac_priv *priv, int queue,
       dma_addr_t dma_addr;
       bool set_ic;

+     /* Ring may be torn down for an XSK pool switch */
+     if (netif_tx_queue_stopped(netdev_get_tx_queue(priv->dev, queue)))
+             return STMMAC_XDP_CONSUMED;
+
       if (stmmac_tx_avail(priv, queue) < STMMAC_TX_THRESH(priv))
               return STMMAC_XDP_CONSUMED;

This is older than your patch, but could you fold it in / add a oatch?

> [...]

Thanks,
Nicolai

Re: [PATCH net v2 2/2] net: stmmac: Stop Tx queue when (en|dis)abling XSK pools

[Kurt Kanzenbach]

[-- Attachment #1: Type: text/plain, Size: 3612 bytes --]

Hi Nicolai,

On Thu Oct 08 2026, Nicolai Buchwitz wrote:
> On 5.10.2026 09:09, Kurt Kanzenbach wrote:
>> When enabling or disabling XSK pools in parallel to Tx traffic, kernel
>> crashes occur. For VLAN tagged frames that happens in stmmac_xmit() ->
>> dwmac4_set_vlan_tag() and for normal frames in stmmac_xmit() ->
>> dwmac4_set_addr(). Both of these functions access the Tx DMA 
>> descriptors.
>> 
>> The XDP pool (en|dis)ablement frees and reallocates the Tx DMA 
>> resources:
>> 
>>  stmmac_disable_tx_queue:
>>    __free_dma_tx_desc_resources
>> 
>>  stmmac_enable_tx_queue:
>>    __alloc_dma_tx_desc_resources
>>    __init_dma_tx_desc_rings
>> 
>> NAPI is disabled during that allocation window, but the Tx queue is not
>> stopped. Therefore, add the stopping of the Tx queue during the 
>> enabling
>> and disabling of XSK pools. Update trans_start when stopping the queue
>> to avoid spurious watchdog timeouts.
>> 
>> The issue can be easily reproduced by:
>> 
>>  1. Run iperf
>>  2. Run application which opens an AF_XDP/ZC socket
>> 
>> Fixes: 132c32ee5bc0 ("net: stmmac: Add TX via XDP zero-copy socket")
>> Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
>> ---
>>  drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c | 14 ++++++++++++++
>>  1 file changed, 14 insertions(+)
>> 
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c 
>> b/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
>> index d7e4db7224b0..883bd3fe8089 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
>> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
>> @@ -6,6 +6,16 @@
>>  #include "stmmac.h"
>>  #include "stmmac_xdp.h"
>> 
>> +static void stmmac_xdp_stop_tx_queue(struct stmmac_priv *priv, u16 
>> queue)
>> +{
>> +	struct netdev_queue *nq = netdev_get_tx_queue(priv->dev, queue);
>> +
>> +	__netif_tx_lock_bh(nq);
>> +	txq_trans_cond_update(nq);
>> +	netif_tx_stop_queue(nq);
>> +	__netif_tx_unlock_bh(nq);
>> +}
>> +
>>  static int stmmac_xdp_enable_pool(struct stmmac_priv *priv,
>>  				  struct xsk_buff_pool *pool, u16 queue)
>>  {
>> @@ -36,6 +46,7 @@ static int stmmac_xdp_enable_pool(struct stmmac_priv 
>> *priv,
>>  	if (need_update) {
>>  		napi_disable(&ch->rx_napi);
>>  		napi_disable(&ch->tx_napi);
>> +		stmmac_xdp_stop_tx_queue(priv, queue);
>
> Unfortunately XDP_TX and ndo_xdp_xmit() ignore the stopped queue and 
> still
> hit the freed ring. I can reproduce this on STM32MP215 with a veth 
> redirect
> into the port while toggling the pool:
>
>    pc : dwmac4_set_addr+0x8/0x18
>    lr : stmmac_xdp_xmit_xdpf+0x1d0/0x3f0
>     stmmac_xdp_xmit+0xe4/0x1a8
>     bq_xmit_all+0xa0/0x208
>     __dev_flush+0x60/0xc0
>     xdp_do_flush+0x134/0x198
>     veth_poll+0x258/0x340
>
> Both go through stmmac_xdp_xmit_xdpf() with the queue lock held, so this
> fixes it for me:
>
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ static int stmmac_xdp_xmit_xdpf(struct stmmac_priv *priv, int queue,
>        dma_addr_t dma_addr;
>        bool set_ic;
>
> +     /* Ring may be torn down for an XSK pool switch */
> +     if (netif_tx_queue_stopped(netdev_get_tx_queue(priv->dev, queue)))
> +             return STMMAC_XDP_CONSUMED;
> +
>        if (stmmac_tx_avail(priv, queue) < STMMAC_TX_THRESH(priv))
>                return STMMAC_XDP_CONSUMED;
>
> This is older than your patch, but could you fold it in / add a oatch?

Thanks a lot for testing! I'll fold it in for next version.

Thanks,
Kurt

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Re: [PATCH net v2 2/2] net: stmmac: Stop Tx queue when (en|dis)abling XSK pools

[Maciej Fijalkowski]

On Mon, Oct 05, 2026 at 09:09:33AM +0200, Kurt Kanzenbach wrote:
> When enabling or disabling XSK pools in parallel to Tx traffic, kernel
> crashes occur. For VLAN tagged frames that happens in stmmac_xmit() ->
> dwmac4_set_vlan_tag() and for normal frames in stmmac_xmit() ->
> dwmac4_set_addr(). Both of these functions access the Tx DMA descriptors.
> 
> The XDP pool (en|dis)ablement frees and reallocates the Tx DMA resources:
> 
>  stmmac_disable_tx_queue:
>    __free_dma_tx_desc_resources
> 
>  stmmac_enable_tx_queue:
>    __alloc_dma_tx_desc_resources
>    __init_dma_tx_desc_rings
> 
> NAPI is disabled during that allocation window, but the Tx queue is not
> stopped. Therefore, add the stopping of the Tx queue during the enabling
> and disabling of XSK pools. Update trans_start when stopping the queue
> to avoid spurious watchdog timeouts.
> 
> The issue can be easily reproduced by:
> 
>  1. Run iperf
>  2. Run application which opens an AF_XDP/ZC socket
> 
> Fixes: 132c32ee5bc0 ("net: stmmac: Add TX via XDP zero-copy socket")
> Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
> index d7e4db7224b0..883bd3fe8089 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
> @@ -6,6 +6,16 @@
>  #include "stmmac.h"
>  #include "stmmac_xdp.h"
>  
> +static void stmmac_xdp_stop_tx_queue(struct stmmac_priv *priv, u16 queue)
> +{
> +	struct netdev_queue *nq = netdev_get_tx_queue(priv->dev, queue);
> +
> +	__netif_tx_lock_bh(nq);
> +	txq_trans_cond_update(nq);
> +	netif_tx_stop_queue(nq);
> +	__netif_tx_unlock_bh(nq);
> +}
> +
>  static int stmmac_xdp_enable_pool(struct stmmac_priv *priv,
>  				  struct xsk_buff_pool *pool, u16 queue)
>  {
> @@ -36,6 +46,7 @@ static int stmmac_xdp_enable_pool(struct stmmac_priv *priv,
>  	if (need_update) {
>  		napi_disable(&ch->rx_napi);
>  		napi_disable(&ch->tx_napi);
> +		stmmac_xdp_stop_tx_queue(priv, queue);

FWIW you can look at what I did at ice driver (ice_qp_dis()) where I used
a bigger hammer here; I think updating trans_start is kinda a workaround.

https://lore.kernel.org/netdev/20240708221416.625850-1-anthony.l.nguyen@intel.com/

>  		stmmac_disable_rx_queue(priv, queue);
>  		stmmac_disable_tx_queue(priv, queue);
>  	}
> @@ -46,6 +57,7 @@ static int stmmac_xdp_enable_pool(struct stmmac_priv *priv,
>  		stmmac_enable_rx_queue(priv, queue);
>  		stmmac_enable_tx_queue(priv, queue);
>  		napi_enable(&ch->rxtx_napi);
> +		netif_tx_wake_queue(netdev_get_tx_queue(priv->dev, queue));
>  
>  		err = stmmac_xsk_wakeup(priv->dev, queue, XDP_WAKEUP_RX);
>  		if (err)
> @@ -73,6 +85,7 @@ static int stmmac_xdp_disable_pool(struct stmmac_priv *priv, u16 queue)
>  
>  	if (need_update) {
>  		napi_disable(&ch->rxtx_napi);
> +		stmmac_xdp_stop_tx_queue(priv, queue);
>  		stmmac_disable_rx_queue(priv, queue);
>  		stmmac_disable_tx_queue(priv, queue);
>  		synchronize_rcu();
> @@ -87,6 +100,7 @@ static int stmmac_xdp_disable_pool(struct stmmac_priv *priv, u16 queue)
>  		stmmac_enable_tx_queue(priv, queue);
>  		napi_enable(&ch->rx_napi);
>  		napi_enable(&ch->tx_napi);
> +		netif_tx_wake_queue(netdev_get_tx_queue(priv->dev, queue));
>  	}
>  
>  	return 0;
> 
> -- 
> 2.47.3
> 
> 

Re: [PATCH net v2 2/2] net: stmmac: Stop Tx queue when (en|dis)abling XSK pools

[Kurt Kanzenbach]

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Hi Maciej,

On Thu Oct 08 2026, Maciej Fijalkowski wrote:
> On Mon, Oct 05, 2026 at 09:09:33AM +0200, Kurt Kanzenbach wrote:
>> When enabling or disabling XSK pools in parallel to Tx traffic, kernel
>> crashes occur. For VLAN tagged frames that happens in stmmac_xmit() ->
>> dwmac4_set_vlan_tag() and for normal frames in stmmac_xmit() ->
>> dwmac4_set_addr(). Both of these functions access the Tx DMA descriptors.
>> 
>> The XDP pool (en|dis)ablement frees and reallocates the Tx DMA resources:
>> 
>>  stmmac_disable_tx_queue:
>>    __free_dma_tx_desc_resources
>> 
>>  stmmac_enable_tx_queue:
>>    __alloc_dma_tx_desc_resources
>>    __init_dma_tx_desc_rings
>> 
>> NAPI is disabled during that allocation window, but the Tx queue is not
>> stopped. Therefore, add the stopping of the Tx queue during the enabling
>> and disabling of XSK pools. Update trans_start when stopping the queue
>> to avoid spurious watchdog timeouts.
>> 
>> The issue can be easily reproduced by:
>> 
>>  1. Run iperf
>>  2. Run application which opens an AF_XDP/ZC socket
>> 
>> Fixes: 132c32ee5bc0 ("net: stmmac: Add TX via XDP zero-copy socket")
>> Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
>> ---
>>  drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c | 14 ++++++++++++++
>>  1 file changed, 14 insertions(+)
>> 
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
>> index d7e4db7224b0..883bd3fe8089 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
>> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
>> @@ -6,6 +6,16 @@
>>  #include "stmmac.h"
>>  #include "stmmac_xdp.h"
>>  
>> +static void stmmac_xdp_stop_tx_queue(struct stmmac_priv *priv, u16 queue)
>> +{
>> +	struct netdev_queue *nq = netdev_get_tx_queue(priv->dev, queue);
>> +
>> +	__netif_tx_lock_bh(nq);
>> +	txq_trans_cond_update(nq);
>> +	netif_tx_stop_queue(nq);
>> +	__netif_tx_unlock_bh(nq);
>> +}
>> +
>>  static int stmmac_xdp_enable_pool(struct stmmac_priv *priv,
>>  				  struct xsk_buff_pool *pool, u16 queue)
>>  {
>> @@ -36,6 +46,7 @@ static int stmmac_xdp_enable_pool(struct stmmac_priv *priv,
>>  	if (need_update) {
>>  		napi_disable(&ch->rx_napi);
>>  		napi_disable(&ch->tx_napi);
>> +		stmmac_xdp_stop_tx_queue(priv, queue);
>
> FWIW you can look at what I did at ice driver (ice_qp_dis()) where I used
> a bigger hammer here; I think updating trans_start is kinda a workaround.
>
> https://lore.kernel.org/netdev/20240708221416.625850-1-anthony.l.nguyen@intel.com/
>

Actually, trans_start is already updated by netif_tx_stop_queue(). I'd
just remove txq_trans_cond_update() for next version.

Thanks,
Kurt

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