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

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Date: Sun, 12 May 2024 00:52:23 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Chris Lew <quic_clew@...cinc.com>
Cc: Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konrad.dybcio@...aro.org>, 
	Sibi Sankar <quic_sibis@...cinc.com>, Mathieu Poirier <mathieu.poirier@...aro.org>, 
	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 Thu, 25 Apr 2024 at 22:30, Chris Lew <quic_clew@...cinc.com> wrote:
>
>
> 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, I missed it initially. I think I'd keep the rest of the
changes and expand the lock to cover pdr_get_domain_list().

>
> Thanks!
> Chris



-- 
With best wishes
Dmitry