Re: [PATCH] mac802154: synchronize pending transmissions before stopping the hardware

[Miquel Raynal]

Hi Adi,

On 20/09/2026 at 17:06:55 GMT, Adi Prasan <itsadi2409@xxxxxxxxx> wrote:

> From: Adi <itsadi2409@xxxxxxxxx>
>
> syzbot reports a WARN_ON(current_phy->suspended) splat in
> mac80211_hwsim's mac802154 counterpart, hwsim_hw_xmit():
>
>   WARNING: CPU: 0 PID: 6038 at drivers/net/ieee802154/mac802154_hwsim.c:266
>   hwsim_hw_xmit+0xcbf/0x1540
>   Call Trace:
>    drv_xmit_async
>    ieee802154_tx
>    ieee802154_subif_start_xmit
>    __netdev_start_xmit
>    ...
>    packet_sendmsg
>
> mac802154_slave_close() only calls netif_stop_queue() on the closing
> netdev before tearing the hardware down via ieee802154_stop_device(),
> which calls straight into drv_stop(). netif_stop_queue() merely marks
> the queue as stopped; it does not wait for a transmission that a
> different CPU already passed the "is the queue stopped" check for and
> is currently executing inside ndo_start_xmit(). That thread can still
> be inside drv_xmit_async() -> hwsim_hw_xmit() by the time drv_stop()
> runs and marks the phy suspended, which trips the WARN_ON() (and, on
> real hardware, could still start a transmission after ->stop() has
> torn down the transceiver).
>
> ieee802154_suspend() already knows about this and synchronizes with
> any in-flight transmission via ieee802154_sync_and_hold_queue() plus
> synchronize_net() before calling ieee802154_stop_device(), releasing
> the queue again afterwards. mac802154_slave_close() is missing the
> same synchronization when the last open interface on a phy is closed.
>
> Do the same hold/sync/release dance in mac802154_slave_close() so
> drv_stop() cannot race with a transmission that is already in flight.
>
> Reported-by: syzbot+adb0bf16414b8bb2d799@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=adb0bf16414b8bb2d799
> Signed-off-by: Adi <itsadi2409@xxxxxxxxx>

We need your real identify.

> ---
>  net/mac802154/iface.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/net/mac802154/iface.c b/net/mac802154/iface.c
> index 31353795fa24..e29f225c0dd1 100644
> --- a/net/mac802154/iface.c
> +++ b/net/mac802154/iface.c
> @@ -313,8 +313,19 @@ static int mac802154_slave_close(struct net_device *dev)
>  
>  	clear_bit(SDATA_STATE_RUNNING, &sdata->state);
>  
> -	if (!local->open_count)
> +	if (!local->open_count) {
> +		/* Ensure any asynchronous transmission already accepted by
> +		 * the driver (i.e. past the netif_stop_queue() above) has
> +		 * fully completed before calling into ->stop(). Otherwise
> +		 * drv_xmit_async() can race with drv_stop(), which some
> +		 * drivers (e.g. mac802154_hwsim) do not expect.

hwsim is for testing purposes, not sure this is a real use case.

> This mirrors
> +		 * the synchronization already done in ieee802154_suspend().
> +		 */

This message is 100% AI generated and can be dropped, unless there is a
real info carried, but I don't see it.

Yet, if we can get rid of these by just fixing max802154_hwsim, please
do it.

> +		ieee802154_sync_and_hold_queue(local);
> +		synchronize_net();
>  		ieee802154_stop_device(local);
> +		ieee802154_release_queue(local);
> +	}
>  
>  	return 0;
>  }

Thanks,
Miquèl