netdev - Re: [PATCH v2 1/1] net: qrtr: start MHI channel after endpoit creation

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Message-ID: <CAMZdPi-ESEHnWVa16tSktLZKOk=r2_2t_S+AwjAx-s3dNwbyTg@mail.gmail.com>
Date:   Sat, 13 Aug 2022 10:45:00 +0200
From:   Loic Poulain <loic.poulain@...aro.org>
To:     Jakub Kicinski <kuba@...nel.org>,
        Maxim Kochetkov <fido_max@...ox.ru>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
        pabeni@...hat.com, linux-arm-msm@...r.kernel.org,
        Hemant Kumar <quic_hemantk@...cinc.com>,
        Manivannan Sadhasivam <mani@...nel.org>
Subject: Re: [PATCH v2 1/1] net: qrtr: start MHI channel after endpoit creation

On Sat, 13 Aug 2022 at 02:09, Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Thu, 11 Aug 2022 12:48:40 +0300 Maxim Kochetkov wrote:
> > MHI channel may generates event/interrupt right after enabling.
> > It may leads to 2 race conditions issues.
> >
> > 1)
> > Such event may be dropped by qcom_mhi_qrtr_dl_callback() at check:
> >
> >       if (!qdev || mhi_res->transaction_status)
> >               return;
> >
> > Because dev_set_drvdata(&mhi_dev->dev, qdev) may be not performed at
> > this moment. In this situation qrtr-ns will be unable to enumerate
> > services in device.
> > ---------------------------------------------------------------
> >
> > 2)
> > Such event may come at the moment after dev_set_drvdata() and
> > before qrtr_endpoint_register(). In this case kernel will panic with
> > accessing wrong pointer at qcom_mhi_qrtr_dl_callback():
> >
> >       rc = qrtr_endpoint_post(&qdev->ep, mhi_res->buf_addr,
> >                               mhi_res->bytes_xferd);
> >
> > Because endpoint is not created yet.
> > --------------------------------------------------------------
> > So move mhi_prepare_for_transfer_autoqueue after endpoint creation
> > to fix it.
> >
> > Fixes: a2e2cc0dbb11 ("net: qrtr: Start MHI channels during init")
> > Signed-off-by: Maxim Kochetkov <fido_max@...ox.ru>
> > Reviewed-by: Hemant Kumar <quic_hemantk@...cinc.com>
> > Reviewed-by: Manivannan Sadhasivam <mani@...nel.org>

Reviewed-by: Loic Poulain <loic.poulain@...aro.org>


>
> You must CC the author of the patch under Fixes, they are usually
> the best person to review the fix. Adding Loic now.
>
> > diff --git a/net/qrtr/mhi.c b/net/qrtr/mhi.c
> > index 18196e1c8c2f..9ced13c0627a 100644
> > --- a/net/qrtr/mhi.c
> > +++ b/net/qrtr/mhi.c
> > @@ -78,11 +78,6 @@ static int qcom_mhi_qrtr_probe(struct mhi_device *mhi_dev,
> >       struct qrtr_mhi_dev *qdev;
> >       int rc;
> >
> > -     /* start channels */
> > -     rc = mhi_prepare_for_transfer_autoqueue(mhi_dev);
> > -     if (rc)
> > -             return rc;
> > -
> >       qdev = devm_kzalloc(&mhi_dev->dev, sizeof(*qdev), GFP_KERNEL);
> >       if (!qdev)
> >               return -ENOMEM;
> > @@ -96,6 +91,13 @@ static int qcom_mhi_qrtr_probe(struct mhi_device *mhi_dev,
> >       if (rc)
> >               return rc;
> >
> > +     /* start channels */
> > +     rc = mhi_prepare_for_transfer_autoqueue(mhi_dev);
> > +     if (rc) {
> > +             qrtr_endpoint_unregister(&qdev->ep);
> > +             return rc;
> > +     }
> > +
> >       dev_dbg(qdev->dev, "Qualcomm MHI QRTR driver probed\n");
> >
> >       return 0;
>