netdev - Re: [PATCH net] atlantic: fix deadlock at aq_nic

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Date:   Fri, 14 Oct 2022 14:13:21 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Íñigo Huguet <ihuguet@...hat.com>
Cc:     irusskikh@...vell.com, dbogdanov@...vell.com, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        netdev@...r.kernel.org, Li Liang <liali@...hat.com>
Subject: Re: [PATCH net] atlantic: fix deadlock at aq_nic_stop

> Fix trying to acquire rtnl_lock at the beginning of those functions, and
> returning if NIC closing is ongoing. Also do the "linkstate" stuff in a
> workqueue instead than in a threaded irq, where sleeping or waiting a
> mutex for a long time is discouraged.

What happens when the same interrupt fires again, while the work queue
is still active? The advantage of the threaded interrupt handler is
that the interrupt will be kept disabled, and should not fire again
until the threaded interrupt handler exits.

> +static void aq_nic_linkstate_task(struct work_struct *work)
> +{
> +	struct aq_nic_s *self = container_of(work, struct aq_nic_s,
> +					     linkstate_task);
> +
> +#if IS_ENABLED(CONFIG_MACSEC)
> +	/* avoid deadlock at aq_nic_stop -> cancel_work_sync */
> +	while (!rtnl_trylock()) {
> +		if (aq_utils_obj_test(&self->flags, AQ_NIC_FLAG_CLOSING))
> +			return;
> +		msleep(AQ_TASK_RETRY_MS);
> +	}
> +#endif
> +
>  	aq_nic_update_link_status(self);
>  
> +#if IS_ENABLED(CONFIG_MACSEC)
> +	rtnl_unlock();
> +#endif
> +

If MACSEC is enabled, aq_nic_update_link_status() is called with RTNL
held. If it is not enabled, RTNL is not held. This sort of
inconsistency could lead to further locking bugs, since it is not
obvious. Please try to make this consistent.

	 Andrew