netdev - Re: [PATCH net-next 4/8] ionic: add work item for missed-doorbell check

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Date: Wed, 12 Jun 2024 18:19:00 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Shannon Nelson <shannon.nelson@....com>
Cc: <netdev@...r.kernel.org>, <davem@...emloft.net>, <edumazet@...gle.com>,
 <pabeni@...hat.com>, <brett.creeley@....com>, <drivers@...sando.io>
Subject: Re: [PATCH net-next 4/8] ionic: add work item for missed-doorbell
 check

On Mon, 10 Jun 2024 16:07:02 -0700 Shannon Nelson wrote:
> +static void ionic_napi_schedule_do_softirq(struct napi_struct *napi)
> +{
> +	if (napi_schedule_prep(napi)) {
> +		local_bh_disable();
> +		__napi_schedule(napi);
> +		local_bh_enable();

No need to open code napi_schedule()

	local_bh_disable();
	napi_schedule(napi);
	local_bh_enable();

is a fairly well-established pattern

> +	}
> +}

> +static void ionic_doorbell_check_dwork(struct work_struct *work)
> +{
> +	struct ionic *ionic = container_of(work, struct ionic,
> +					   doorbell_check_dwork.work);
> +	struct ionic_lif *lif = ionic->lif;
> +
> +	if (test_bit(IONIC_LIF_F_FW_STOPPING, lif->state) ||
> +	    test_bit(IONIC_LIF_F_FW_RESET, lif->state))
> +		return;
> +
> +	mutex_lock(&lif->queue_lock);

This will deadlock under very inopportune circumstances, no?

The best way of implementing periodic checks using a workqueue is to
only cancel it sync from the .remove callback, before you free the
netdev. Otherwise cancel it non-sync or don't cancel at all, and once
it takes the lock double check the device is still actually running.