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Subject: Re: [PATCH v2] ARM: Add sanity check for dev->periphid in
 amba_probe()
To:     "Russell King (Oracle)" <linux@armlinux.org.uk>
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>
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>
 <Yw3hfGV4DYyJ0Gno@shell.armlinux.org.uk>
From:   "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
Message-ID: <2452e7b0-d4fd-2e27-a336-bf87b85a8d50@huawei.com>
Date:   Tue, 30 Aug 2022 18:31:14 +0800
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On 2022/8/30 18:07, Russell King (Oracle) wrote:
> 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().

Oh, I was careless. I think it's drv->match. But the processing flow
will continue to go to "dev->bus->probe".

__driver_attach():
        ret = driver_match_device(drv, dev);
        if (ret == 0) {
                /* no match */
                return 0;
        } else if (ret == -EPROBE_DEFER) {               <------no return in this branch
                dev_dbg(dev, "Device match requests probe deferral\n");
                dev->can_match = true;
                driver_deferred_probe_add(dev);
        } else if (ret < 0) {
                dev_dbg(dev, "Bus failed to match device: %d\n", ret);
                return ret;
        } /* ret > 0 means positive match */

        ... ...
        driver_probe_device(drv, dev);
             ......
                  dev->bus->probe


> 

-- 
Regards,
  Zhen Lei