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Date:   Fri, 13 Aug 2021 17:46:55 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     Alex Elder <elder@linaro.org>
Cc:     davem@davemloft.net, bjorn.andersson@linaro.org,
        evgreen@chromium.org, cpratapa@codeaurora.org,
        subashab@codeaurora.org, elder@kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next 4/6] net: ipa: ensure hardware has power in
 ipa_start_xmit()
Message-ID: <20210813174655.1d13b524@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
In-Reply-To: <20210812195035.2816276-5-elder@linaro.org>
References: <20210812195035.2816276-1-elder@linaro.org>
        <20210812195035.2816276-5-elder@linaro.org>
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Precedence: bulk

On Thu, 12 Aug 2021 14:50:33 -0500 Alex Elder wrote:
> +	/* The hardware must be powered for us to transmit */
> +	dev = &ipa->pdev->dev;
> +	ret = pm_runtime_get(dev);
> +	if (ret < 1) {
> +		/* If a resume won't happen, just drop the packet */
> +		if (ret < 0 && ret != -EINPROGRESS) {
> +			pm_runtime_put_noidle(dev);
> +			goto err_drop_skb;
> +		}

This is racy, what if the pm work gets scheduled on another CPU and
calls wake right here (i.e. before you call netif_stop_queue())?
The queue may never get woken up?

> +		/* No power (yet).  Stop the network stack from transmitting
> +		 * until we're resumed; ipa_modem_resume() arranges for the
> +		 * TX queue to be started again.
> +		 */
> +		netif_stop_queue(netdev);
> +
> +		(void)pm_runtime_put(dev);
> +
> +		return NETDEV_TX_BUSY;