Re: [PATCH net 1/1] net: stmmac: Use rtnl_lock/unlock on netif_set_real_num_rx_queues() call

[Jakub Kicinski]

On Thu, 12 Nov 2020 22:49:48 +0800 Wong Vee Khee wrote:
> Fix an issue where dump stack is printed on suspend resume flow due to
> netif_set_real_num_rx_queues() is not called with rtnl_lock held().
> 
> Fixes: 686cff3d7022 ("net: stmmac: Fix incorrect location to set real_num_rx|tx_queues")
> Reported-by: Christophe ROULLIER <christophe.roullier@xxxxxx>
> Tested-by: Christophe ROULLIER <christophe.roullier@xxxxxx>
> Cc: Alexandre TORGUE <alexandre.torgue@xxxxxx>
> Reviewed-by: Ong Boon Leong <boon.leong.ong@xxxxxxxxx>
> Signed-off-by: Wong Vee Khee <vee.khee.wong@xxxxxxxxx>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index ba855465a2db..33e280040000 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -5278,7 +5278,10 @@ int stmmac_resume(struct device *dev)
>  
>  	stmmac_clear_descriptors(priv);
>  
> +	rtnl_lock();
>  	stmmac_hw_setup(ndev, false);
> +	rtnl_unlock();
> +
>  	stmmac_init_coalesce(priv);
>  	stmmac_set_rx_mode(ndev);
>  

Doesn't look quite right. This is under the priv->lock which is
sometimes taken under rtnl_lock. So theoretically there could be
a deadlock.

You should probably take rtnl_lock() before priv->lock and release 
it after. It's pretty common for drivers to hold rtnl_lock around 
most of the resume method.

With larger context:
 

        mutex_lock(&priv->lock);
 
        stmmac_reset_queues_param(priv);
 
        stmmac_clear_descriptors(priv);
 
+       rtnl_lock();
        stmmac_hw_setup(ndev, false);
+       rtnl_unlock();
+
        stmmac_init_coalesce(priv);
        stmmac_set_rx_mode(ndev);
 
        stmmac_restore_hw_vlan_rx_fltr(priv, ndev, priv->hw);
 
        stmmac_enable_all_queues(priv);
 
        mutex_unlock(&priv->lock);