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From:   Stephen Boyd <swboyd@chromium.org>
User-Agent: alot/0.9.1
Date:   Wed, 12 Jan 2022 20:25:39 -0800
Message-ID: <CAE-0n53FAHDmCznJ35Xh2aTwXBVwukAM3ioKx8SU9VowSaQSqA@mail.gmail.com>
Subject: Re: [PATCH v5 25/32] iommu/mtk: Migrate to aggregate driver
To:     Yong Wu <yong.wu@mediatek.com>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Douglas Anderson <dianders@chromium.org>,
        linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org,
        Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Rob Clark <robdclark@gmail.com>,
        Russell King <rmk+kernel@arm.linux.org.uk>,
        Saravana Kannan <saravanak@google.com>,
        linux-mediatek@lists.infradead.org,
        iommu@lists.linux-foundation.org, youlin.pei@mediatek.com
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Quoting Yong Wu (2022-01-12 01:09:19)
> On Tue, 2022-01-11 at 16:27 -0800, Stephen Boyd wrote:
> > ---8<---
> > diff --git a/drivers/base/component.c b/drivers/base/component.c
> > index 64ad7478c67a..97f253a41bdf 100644
> > --- a/drivers/base/component.c
> > +++ b/drivers/base/component.c
> > @@ -492,15 +492,30 @@ static struct aggregate_device
> > *__aggregate_find(struct device *parent)
> >       return dev ? to_aggregate_device(dev) : NULL;
> >  }
> >
> > +static DEFINE_MUTEX(aggregate_mutex);
> > +
> >  static int aggregate_driver_register(struct aggregate_driver *adrv)
> >  {
> > -     adrv->driver.bus = &aggregate_bus_type;
> > -     return driver_register(&adrv->driver);
> > +     int ret = 0;
> > +
> > +     mutex_lock(&aggregate_mutex);
> > +     if (!refcount_inc_not_zero(&adrv->count)) {
> > +             adrv->driver.bus = &aggregate_bus_type;
> > +             ret = driver_register(&adrv->driver);
> > +             if (!ret)
> > +                     refcount_inc(&adrv->count);
>
> This should be refcount_set(&adrv->count, 1)?
>
> Otherwise, it will warning like this:

Yeah I'll fix it, thanks.

>
> [    2.654526] ------------[ cut here ]------------
> [    2.655558] refcount_t: addition on 0; use-after-free.
>
> After this patch, the aggregate_driver flow looks ok. But our driver
> still aborts like this:
>
> [    2.721316] Unable to handle kernel NULL pointer dereference at
> virtual address 0000000000000000
> ...
> [    2.731658] pc : mtk_smi_larb_config_port_gen2_general+0xa4/0x138
> [    2.732434] lr : mtk_smi_larb_resume+0x54/0x98
> ...
> [    2.742457] Call trace:
> [    2.742768]  mtk_smi_larb_config_port_gen2_general+0xa4/0x138
> [    2.743496]  pm_generic_runtime_resume+0x2c/0x48
> [    2.744090]  __genpd_runtime_resume+0x30/0xa8
> [    2.744648]  genpd_runtime_resume+0x94/0x2c8
> [    2.745191]  __rpm_callback+0x44/0x150
> [    2.745669]  rpm_callback+0x6c/0x78
> [    2.746114]  rpm_resume+0x314/0x558
> [    2.746559]  __pm_runtime_resume+0x3c/0x88
> [    2.747080]  pm_runtime_get_suppliers+0x7c/0x110
> [    2.747668]  __driver_probe_device+0x4c/0xe8
> [    2.748212]  driver_probe_device+0x44/0x130
> [    2.748745]  __device_attach_driver+0x98/0xd0
> [    2.749300]  bus_for_each_drv+0x68/0xd0
> [    2.749787]  __device_attach+0xec/0x148
> [    2.750277]  device_attach+0x14/0x20
> [    2.750733]  bus_rescan_devices_helper+0x50/0x90
> [    2.751319]  bus_for_each_dev+0x7c/0xd8
> [    2.751806]  bus_rescan_devices+0x20/0x30
> [    2.752315]  __component_add+0x7c/0xa0
> [    2.752795]  component_add+0x14/0x20
> [    2.753253]  mtk_smi_larb_probe+0xe0/0x120
>
> This is because the device runtime_resume is called before the bind
> operation(In our case this detailed function is mtk_smi_larb_bind).
> The issue doesn't happen without this patchset. I'm not sure the right
> sequence. If we should fix in mediatek driver, the patch could be:

Oh, the runtime PM is moved around with these patches. The aggregate
device is runtime PM enabled before the probe is called, and there are
supplier links made to each component, so each component is runtime
resumed before the aggregate probe function is called. It means that all
the component drivers need to have their resources ready to power on
before their component_bind() callback is made. Thinking more about it
that may be wrong if something from the aggregate device is needed to
fully power on the component. Is that what is happening here?

>
>
> diff --git a/drivers/memory/mtk-smi.c b/drivers/memory/mtk-smi.c
> index b883dcc0bbfa..288841555067 100644
> --- a/drivers/memory/mtk-smi.c
> +++ b/drivers/memory/mtk-smi.c
> @@ -483,8 +483,9 @@ static int __maybe_unused
> mtk_smi_larb_resume(struct device *dev)
>         if (ret < 0)
>                 return ret;
>
> -       /* Configure the basic setting for this larb */
> -       larb_gen->config_port(dev);
> +       /* Configure the basic setting for this larb after it binds
> with iommu */
> +       if (larb->mmu)
> +               larb_gen->config_port(dev);
>
>         return 0;
>  }
>
>
> Another nitpick, the title should be: iommu/mediatek: xxxx
>

Fixed it.