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SubjectRe: [PATCH net 1/1] net: stmmac: Use rtnl_lock/unlock on netif_set_real_num_rx_queues() call
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@st.com>
> Tested-by: Christophe ROULLIER <christophe.roullier@st.com>
> Cc: Alexandre TORGUE <alexandre.torgue@st.com>
> Reviewed-by: Ong Boon Leong <boon.leong.ong@intel.com>
> Signed-off-by: Wong Vee Khee <vee.khee.wong@intel.com>
> ---
> 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);


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