[Bug 110421] New: Reading debugfs file /sys/kernel/debug/dri/0/amdgpu_regs hangs the machine

[Bug 110421] New: Reading debugfs file /sys/kernel/debug/dri/0/amdgpu_regs hangs the machine

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=110421

            Bug ID: 110421
           Summary: Reading debugfs file
                    /sys/kernel/debug/dri/0/amdgpu_regs hangs the machine
           Product: Drivers
           Version: 2.5
    Kernel Version: 4.4.0-0.rc8.git0.1.fc24.x86_64
          Hardware: All
                OS: Linux
              Tree: Fedora
            Status: NEW
          Severity: high
          Priority: P1
         Component: Video(DRI - non Intel)
          Assignee: drivers_video-dri@kernel-bugs.osdl.org
          Reporter: rivanvx@gmail.com
        Regression: No

I am using amdgpu driver on

01:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc.
[AMD/ATI] Amethyst XT [Radeon R9 M295X Mac Edition / R9 380X] [1002:6938] (rev
f1)

Running the following script

for i in $(seq 0 65535); do echo -n "$i: "; dd if=amdgpu_regs bs=4 skip=$i
count=1 2>/dev/null | hexdump -e '"%08x"'; echo; done

hangs the machine at register 14829 and the data from the register is not
printed. I tried reading the registers twice just to be sure it hangs in the
same place repeatedly, and it was 14829 in both cases.

I have reports this is reproducible using vanilla kernel.

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[Bug 110421] Reading debugfs file /sys/kernel/debug/dri/0/amdgpu_regs hangs the machine

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=110421

Christian König <deathsimple@vodafone.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |deathsimple@vodafone.de

--- Comment #1 from Christian König <deathsimple@vodafone.de> ---
That's perfectly normal behavior. Register 14829 probably don't exists on your
hardware generation and so accessing it causes an unresolvable BUS stall.

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[Bug 110421] Reading debugfs file /sys/kernel/debug/dri/0/amdgpu_regs hangs the machine

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=110421

--- Comment #2 from Vedran Miletić <rivanvx@gmail.com> ---
Can't anything be done to avoid the hang? Running cat on that file will hang
the machine as well.

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[Bug 110421] Reading debugfs file /sys/kernel/debug/dri/0/amdgpu_regs hangs the machine

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=110421

--- Comment #3 from Christian König <deathsimple@vodafone.de> ---
Not really.

You could do large lists of which registers are save for accessing, but we have
256KB register space and need an individual list for pretty much every hardware
generation.

Sorry but just accessing random registers through the debugfs interface is
simply not expected to work.

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[Bug 110421] Reading debugfs file /sys/kernel/debug/dri/0/amdgpu_regs hangs the machine

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=110421

Vedran Miletić <vedran@miletic.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |WILL_NOT_FIX

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