Re: rtw88: The debugfs interface reads registers from the wrong device

[Kalle Valo <kvalo@kernel.org>]

Ping-Ke Shih <pkshih@realtek.com> writes:

> On Tue, 2024-07-16 at 01:19 +0000, Ping-Ke Shih wrote:
>
>> On Mon, 2024-07-15 at 14:26 +0300, Bitterblue Smith wrote:
>> > On 15/07/2024 14:05, Bitterblue Smith wrote:
>> > > Hi,
>> > > 
>> > > To reproduce the problem, you need a computer with two wifi
>> > > devices supported by rtw88. It's especially easy to notice
>> > > the problem if one of the devices is USB and the other is PCI,
>> > > because the PCI device will have various values in the
>> > > registers 0x300..0x3ff, but the USB device will have all
>> > > 0xeaeaeaea there.
>> > > 
>> > > 1. Let's assume the driver for the PCI device is already loaded.
>> > >    I have RTL8822CE.
>> > > 
>> > > 2. Mount debugfs:
>> > > 
>> > >    # mount -t debugfs none /sys/kernel/debug
>> > > 
>> > > 3. Check page 0x300:
>> > > 
>> > >    # cat /sys/kernel/debug/ieee80211/phy0/rtw88/mac_3
>> > >      00000300  f7138000    33330000    ffffb000    00000000
>> > >      .....
>> > > 
>> > > 4. Plug the USB device. I used RTL8811CU.
>> > > 
>> > > 5. Check page 0x300 again:
>> > > 
>> > >    # cat /sys/kernel/debug/ieee80211/phy0/rtw88/mac_3
>> > >      00000300  eaeaeaea    eaeaeaea    eaeaeaea    eaeaeaea
>> > >      .....
>> > > 
>> > > 6. Bonus: unload rtw88_8821cu and check page 0x300 again to get
>> > >    a null pointer dereference:
>> > > 
>> > >    # rmmod rtw88_8821cu
>> > >    # cat /sys/kernel/debug/ieee80211/phy0/rtw88/mac_3
>> > 
>> > I forgot to say: my kernel is 6.9.8-arch1-1 from Arch Linux.
>> > The problem also happens with kernel 6.9.8 plus rtw88 from
>> > rtw-next.
>> 
>> This limitation is existing since initial driver.
>> 
>> To read a range of large registers area, for example, we need to
>> a range via write operation and store as a private data, and
>> then use read operation with private data to read registers.
>> 
>> The limitation is because the private data is static variable.
>> A possible solution is to duplicate static variable into rtwdev.
>> Not sure if it is worth to adjust codes for debug purpose only.
>> 
>> Another easier solution is to avoid creating debugfs for second
>> adapter. How do you think?
>> 
>
> Think a little bit further. I will try to duplicate static variables
> to support multiple adapters. 

BTW in drivers all static variables need to be const just because of
issues like this. Static non-const variables are a big no.

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