linux-kernel - Re: [PATCH v7 1/6] soc: qcom: pdr: protect locator

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Date: Thu, 25 Apr 2024 12:30:07 -0700
From: Chris Lew <quic_clew@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Bjorn Andersson
	<andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Sibi Sankar
	<quic_sibis@...cinc.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>
CC: <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-remoteproc@...r.kernel.org>,
        Johan Hovold <johan+linaro@...nel.org>,
        Xilin Wu <wuxilin123@...il.com>,
        Bryan O'Donoghue
	<bryan.odonoghue@...aro.org>,
        Neil Armstrong <neil.armstrong@...aro.org>
Subject: Re: [PATCH v7 1/6] soc: qcom: pdr: protect locator_addr with the main
 mutex


On 4/24/2024 2:27 AM, Dmitry Baryshkov wrote:
> If the service locator server is restarted fast enough, the PDR can
> rewrite locator_addr fields concurrently. Protect them by placing
> modification of those fields under the main pdr->lock.
> 
> Fixes: fbe639b44a82 ("soc: qcom: Introduce Protection Domain Restart helpers")
> Tested-by: Neil Armstrong <neil.armstrong@...aro.org> # on SM8550-QRD
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> ---
>   drivers/soc/qcom/pdr_interface.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/soc/qcom/pdr_interface.c b/drivers/soc/qcom/pdr_interface.c
> index a1b6a4081dea..19cfe4b41235 100644
> --- a/drivers/soc/qcom/pdr_interface.c
> +++ b/drivers/soc/qcom/pdr_interface.c
> @@ -76,12 +76,12 @@ static int pdr_locator_new_server(struct qmi_handle *qmi,
>   					      locator_hdl);
>   	struct pdr_service *pds;
>   
> +	mutex_lock(&pdr->lock);
>   	/* Create a local client port for QMI communication */
>   	pdr->locator_addr.sq_family = AF_QIPCRTR;
>   	pdr->locator_addr.sq_node = svc->node;
>   	pdr->locator_addr.sq_port = svc->port;
>   
> -	mutex_lock(&pdr->lock);
>   	pdr->locator_init_complete = true;
>   	mutex_unlock(&pdr->lock);
>   
> @@ -104,10 +104,10 @@ static void pdr_locator_del_server(struct qmi_handle *qmi,
>   
>   	mutex_lock(&pdr->lock);
>   	pdr->locator_init_complete = false;
> -	mutex_unlock(&pdr->lock);
>   
>   	pdr->locator_addr.sq_node = 0;
>   	pdr->locator_addr.sq_port = 0;
> +	mutex_unlock(&pdr->lock);
>   }
>   
>   static const struct qmi_ops pdr_locator_ops = {
> 

These two functions are provided as qmi_ops handlers in pdr_locator_ops. 
Aren't they serialized in the qmi handle's workqueue since it as an 
ordered_workqueue? Even in a fast pdr scenario I don't think we would 
see a race condition between these two functions.

The other access these two functions do race against is in the 
pdr_notifier_work. I think you would need to protect locator_addr in 
pdr_get_domain_list since the qmi_send_request there uses 
'pdr->locator_addr'.

Thanks!
Chris