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Date:   Tue, 30 Aug 2022 11:07:56 +0100
From:   "Russell King (Oracle)" <linux@armlinux.org.uk>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
Cc:     Saravana Kannan <saravanak@google.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        patches@armlinux.org.uk, Kefeng Wang <wangkefeng.wang@huawei.com>,
        Linus Walleij <linus.walleij@linaro.org>
Subject: Re: [PATCH v2] ARM: Add sanity check for dev->periphid in
 amba_probe()
Message-ID: <Yw3hfGV4DYyJ0Gno@shell.armlinux.org.uk>
References: <20220830065413.638-1-thunder.leizhen@huawei.com>
 <CAGETcx8hfzAthF_gCMrmnVOgwgFJEPE=bwRuVeXaiB7ywUkWkg@mail.gmail.com>
 <Yw3cs6wb4PvnDN/7@shell.armlinux.org.uk>
 <b120e94b-4b43-6d8a-a136-41417cb250cc@huawei.com>
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On Tue, Aug 30, 2022 at 06:03:31PM +0800, Leizhen (ThunderTown) wrote:
> 
> 
> On 2022/8/30 17:47, Russell King (Oracle) wrote:
> > On Tue, Aug 30, 2022 at 12:20:00AM -0700, Saravana Kannan wrote:
> >> On Mon, Aug 29, 2022 at 11:59 PM Zhen Lei <thunder.leizhen@huawei.com> wrote:
> >>>
> >>> Commit f2d3b9a46e0e ("ARM: 9220/1: amba: Remove deferred device addition")
> >>> forcibly invokes device_add() even if dev->periphid is not ready. Although
> >>> it will be remedied in amba_match(): dev->periphid will be initialized
> >>> if everything is in place; Otherwise, return -EPROBE_DEFER to block
> >>> __driver_attach() from further execution. But not all drivers have .match
> >>> hook, such as pl031, the dev->bus->probe will be called directly in
> >>> __driver_attach(). Unfortunately, if dev->periphid is still not
> >>> initialized, the following exception will be triggered.
> >>>
> >>> 8<--- cut here ---
> >>> Unable to handle kernel NULL pointer dereference at virtual address 00000008
> >>> [00000008] *pgd=00000000
> >>> Internal error: Oops: 5 [#1] SMP ARM
> >>> Modules linked in:
> >>> CPU: 1 PID: 1 Comm: swapper/0 Not tainted 6.0.0-rc2+ #7
> >>> Hardware name: ARM-Versatile Express
> >>> PC is at pl031_probe+0x8/0x208
> >>> LR is at amba_probe+0xf0/0x160
> >>> pc : 80698df8  lr : 8050eb54  psr: 80000013
> >>> sp : c0825df8  ip : 00000000  fp : 811fda38
> >>> r10: 00000000  r9 : 80d72470  r8 : fffffdfb
> >>> r7 : 811fd800  r6 : be7eb330  r5 : 00000000  r4 : 811fd900
> >>> r3 : 80698df0  r2 : 37000000  r1 : 00000000  r0 : 811fd800
> >>> Flags: Nzcv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
> >>> Control: 10c5387d  Table: 6000406a  DAC: 00000051
> >>> ... ...
> >>>  pl031_probe from amba_probe+0xf0/0x160
> >>>  amba_probe from really_probe+0x118/0x290
> >>>  really_probe from __driver_probe_device+0x84/0xe4
> >>>  __driver_probe_device from driver_probe_device+0x30/0xd0
> >>>  driver_probe_device from __driver_attach+0x8c/0xfc
> >>>  __driver_attach from bus_for_each_dev+0x70/0xb0
> >>>  bus_for_each_dev from bus_add_driver+0x168/0x1f4
> >>>  bus_add_driver from driver_register+0x7c/0x118
> >>>  driver_register from do_one_initcall+0x44/0x1ec
> >>>  do_one_initcall from kernel_init_freeable+0x238/0x288
> >>>  kernel_init_freeable from kernel_init+0x18/0x12c
> >>>  kernel_init from ret_from_fork+0x14/0x2c
> >>> ... ...
> >>> ---[ end trace 0000000000000000 ]---
> >>>
> >>> Therefore, take the same action as in amba_match(): return -EPROBE_DEFER
> >>> if dev->periphid is not ready in amba_probe().
> >>>
> >>> Fixes: f2d3b9a46e0e ("ARM: 9220/1: amba: Remove deferred device addition")
> >>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> >>> ---
> >>> KernelVersion: v6.0-rc3
> >>>  drivers/amba/bus.c | 24 +++++++++++++++++++++---
> >>>  1 file changed, 21 insertions(+), 3 deletions(-)
> >>>
> >>> v1 --> v2:
> >>> 1. Update this patch based on:
> >>>    https://lore.kernel.org/lkml/20220818172852.3548-1-isaacmanjarres@google.com/
> >>> 2. Move the operations of sanity checking and reading dev->periphid,
> >>>    updating uevent into new function amba_prepare_periphid().
> >>>
> >>> diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> >>> index 110a535648d2e1f..8e4c7e190880206 100644
> >>> --- a/drivers/amba/bus.c
> >>> +++ b/drivers/amba/bus.c
> >>> @@ -204,10 +204,9 @@ static int amba_read_periphid(struct amba_device *dev)
> >>>         return ret;
> >>>  }
> >>>
> >>> -static int amba_match(struct device *dev, struct device_driver *drv)
> >>> +static int amba_prepare_periphid(struct device *dev)
> >>>  {
> >>>         struct amba_device *pcdev = to_amba_device(dev);
> >>> -       struct amba_driver *pcdrv = to_amba_driver(drv);
> >>>
> >>>         mutex_lock(&pcdev->periphid_lock);
> >>>         if (!pcdev->periphid) {
> >>> @@ -228,6 +227,19 @@ static int amba_match(struct device *dev, struct device_driver *drv)
> >>>         }
> >>>         mutex_unlock(&pcdev->periphid_lock);
> >>>
> >>> +       return 0;
> >>> +}
> >>> +
> >>> +static int amba_match(struct device *dev, struct device_driver *drv)
> >>> +{
> >>> +       struct amba_device *pcdev = to_amba_device(dev);
> >>> +       struct amba_driver *pcdrv = to_amba_driver(drv);
> >>> +       int ret;
> >>> +
> >>> +       ret = amba_prepare_periphid(dev);
> >>> +       if (ret)
> >>> +               return ret;
> >>> +
> >>>         /* When driver_override is set, only bind to the matching driver */
> >>>         if (pcdev->driver_override)
> >>>                 return !strcmp(pcdev->driver_override, drv->name);
> >>> @@ -278,9 +290,15 @@ static int amba_probe(struct device *dev)
> >>>  {
> >>>         struct amba_device *pcdev = to_amba_device(dev);
> >>>         struct amba_driver *pcdrv = to_amba_driver(dev->driver);
> >>> -       const struct amba_id *id = amba_lookup(pcdrv->id_table, pcdev);
> >>> +       const struct amba_id *id;
> >>>         int ret;
> >>>
> >>> +       ret = amba_prepare_periphid(dev);
> >>> +       if (ret)
> >>> +               return ret;
> >>> +
> >>> +       id = amba_lookup(pcdrv->id_table, pcdev);
> >>> +
> >>>         do {
> >>>                 ret = of_amba_device_decode_irq(pcdev);
> >>>                 if (ret)
> >>
> >> Let's wait for Isaac to review this. He has been looking at the
> >> locking issue for a bit and there were some tricky cases.
> > 
> > How can we get to amba_probe() if amba_match() has not returned a
> > positive match for an ID? Surely if that happens, the driver model
> 
> Always return true.
> 
> __driver_attach
>     driver_match_device
> 
> static inline int driver_match_device(struct device_driver *drv,
>                                       struct device *dev)
> {
>         return drv->bus->match ? drv->bus->match(dev, drv) : 1;
> }

You seem to be misunderstanding something rather fundamental here.

For an amba driver, drv->bus will always be pointing at amba_bustype.
That always has a "match" operation. Therefore, the default of '1'
above will *never* be used for an AMBA driver.

If drv->bus does not point at amba_bustype, then amba_probe() will
not be called for "drv".

Therefore, amba_match() must always be called before amba_probe().

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