Re: [PATCH v6 19/24] drm/bridge: dumb-vga-dac: Provide ddc symlink in connector sysfs directory

[Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org>]

On Fri, Jul 26, 2019 at 07:23:13PM +0200, Andrzej Pietrasiewicz wrote:
> Use the ddc pointer provided by the generic connector.
> 
> Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
> Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>

This patch results in a crash when running qemu:versatilepb.

Unable to handle kernel NULL pointer dereference at virtual address 000000c5
pgd = (ptrval)
[000000c5] *pgd=00000000
Internal error: Oops: 5 [#1] ARM
Modules linked in:
CPU: 0 PID: 1 Comm: swapper Not tainted 5.3.0-rc1+ #1
Hardware name: ARM-Versatile (Device Tree Support)
PC is at sysfs_do_create_link_sd+0x38/0xd8
LR is at sysfs_do_create_link_sd+0x38/0xd8
pc : [<c01ac94c>]    lr : [<c01ac94c>]    psr: a0000153
sp : c783bd18  ip : 00000000  fp : c783bde8
r10: c7ef5ea8  r9 : 00000001  r8 : c0955dc0
r7 : c73cb5b0  r6 : c73cd800  r5 : 000000ad  r4 : 00000000
r3 : c7838ae0  r2 : 00000000  r1 : 00000008  r0 : c0aa2898
Flags: NzCv  IRQs on  FIQs off  Mode SVC_32  ISA ARM  Segment none
Control: 00093177  Table: 00004000  DAC: 00000053
Process swapper (pid: 1, stack limit = 0x(ptrval))
Stack: (0xc783bd18 to 0xc783c000)
bd00:                                                       c73ccc48 c73ccc74
bd20: c73cd800 c0ac7c88 00000000 c729cc80 c7ef5ea8 c04c7fc0 c73ccc48 c0a73068
bd40: c73cd800 c0ac7c88 00000000 c04c87e0 00000001 00000000 c04cefcc c04dc3f8
bd60: c73a9030 c73cd800 c73ccc48 7fc2ce37 00000000 c73cd800 00000000 c04cefcc
bd80: c73cd800 00000000 00000000 c04b4ebc c0a73068 c7ef5ea8 c783bde8 c049ffcc
bda0: c73a9020 c73cd800 c78e6000 c73a9020 00000000 c73a9020 c0a73068 c04df2f8
bdc0: c783bde8 c095a76c c73a9020 c0065744 c73ccc20 c73a9020 00000000 00000001
bde0: c7838ae0 00000000 c73ccc20 7fc2ce37 00000000 c78e6000 00000000 c0ac7c34
be00: c07dc1f8 00000000 00000000 c0a6b384 c0a59858 c045e8d8 c78e6000 c1173a78
be20: 00000000 c0ac7c34 00000000 c04e77c4 c78e6000 c0ac7c34 c0ac7c34 c0a73068
be40: 00000000 ffffe000 c0a6b384 c04e7a34 c0ac7c34 c0ac7c34 c0a73068 c78e6000
be60: 00000000 c0ac7c34 c0a73068 00000000 ffffe000 c0a6b384 c0a59858 c04e7cf0
be80: 00000000 c0ac7c34 c78e6000 c04e7d7c 00000000 c0ac7c34 c04e7cf8 c04e5928
bea0: c73b2800 c78d88a0 c78dd110 7fc2ce37 ffffe000 c0ac7c34 c73b2800 c0ac16e0
bec0: 00000000 c04e6b28 c095a73c c0af0a60 c0a73068 c0ac7c34 c0af0a60 c0a73068
bee0: c0a401c4 c04e8968 ffffe000 c0af0a60 c0a73068 c000b3bc 00000115 00000000
bf00: c7ffce6c c7ffce00 c09e15b0 00000115 00000115 c0048844 c09e000c c097cfd4
bf20: 00000000 00000006 00000006 00000000 00000000 c7ffce6c ffffe000 c006954c
bf40: ffffe000 7fc2ce37 c0afb000 c0af0a60 00000115 c0afb000 00000007 c0a59850
bf60: ffffe000 c0a111e8 00000006 00000006 00000000 c0a10678 00000000 7fc2ce37
bf80: 00000000 00000000 c07824cc 00000000 00000000 00000000 00000000 00000000
bfa0: 00000000 c07824d4 00000000 c00090b0 00000000 00000000 00000000 00000000
bfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
bfe0: 00000000 00000000 00000000 00000000 00000013 00000000 00000000 00000000
[<c01ac94c>] (sysfs_do_create_link_sd) from [<c04c7fc0>] (drm_connector_register.part.1+0x40/0xa0)
[<c04c7fc0>] (drm_connector_register.part.1) from [<c04c87e0>] (drm_connector_register_all+0x90/0xb8)
[<c04c87e0>] (drm_connector_register_all) from [<c04cefcc>] (drm_modeset_register_all+0x44/0x6c)
[<c04cefcc>] (drm_modeset_register_all) from [<c04b4ebc>] (drm_dev_register+0x15c/0x1c0)
[<c04b4ebc>] (drm_dev_register) from [<c04df2f8>] (pl111_amba_probe+0x2e0/0x4ac)
[<c04df2f8>] (pl111_amba_probe) from [<c045e8d8>] (amba_probe+0x9c/0x118)
[<c045e8d8>] (amba_probe) from [<c04e77c4>] (really_probe+0x1c0/0x2bc)
[<c04e77c4>] (really_probe) from [<c04e7a34>] (driver_probe_device+0x5c/0x170)
[<c04e7a34>] (driver_probe_device) from [<c04e7cf0>] (device_driver_attach+0x58/0x60)
[<c04e7cf0>] (device_driver_attach) from [<c04e7d7c>] (__driver_attach+0x84/0xc0)
[<c04e7d7c>] (__driver_attach) from [<c04e5928>] (bus_for_each_dev+0x70/0xb4)
[<c04e5928>] (bus_for_each_dev) from [<c04e6b28>] (bus_add_driver+0x154/0x1e0)
[<c04e6b28>] (bus_add_driver) from [<c04e8968>] (driver_register+0x74/0x108)
[<c04e8968>] (driver_register) from [<c000b3bc>] (do_one_initcall+0x84/0x2e4)
[<c000b3bc>] (do_one_initcall) from [<c0a111e8>] (kernel_init_freeable+0x2bc/0x394)
[<c0a111e8>] (kernel_init_freeable) from [<c07824d4>] (kernel_init+0x8/0xf0)
[<c07824d4>] (kernel_init) from [<c00090b0>] (ret_from_fork+0x14/0x24)
Exception stack(0xc783bfb0 to 0xc783bff8)
bfa0:                                     00000000 00000000 00000000 00000000
bfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
bfe0: 00000000 00000000 00000000 00000000 00000013 00000000
Code: e59f00a0 e1a09003 e1a08002 eb176e54 (e5955018) 
---[ end trace f503b374936886c5 ]---

Bisect log attached.

Guenter

---
# bad: [3880be629e26f6c407593602398c6651860d5fae] Add linux-next specific files for 20190807
# good: [e21a712a9685488f5ce80495b37b9fdbe96c230d] Linux 5.3-rc3
git bisect start 'HEAD' 'v5.3-rc3'
# good: [83d74da9e6d2ca78b32e9e794c6bcbd433d5efaa] Merge remote-tracking branch 'crypto/master'
git bisect good 83d74da9e6d2ca78b32e9e794c6bcbd433d5efaa
# bad: [3add021bff629f1792a5e4268afe13b3047b5523] Merge remote-tracking branch 'sound/for-next'
git bisect bad 3add021bff629f1792a5e4268afe13b3047b5523
# good: [4ef58ee18a654b1992d00281501d6eff051a0c5e] Merge remote-tracking branch 'amdgpu/drm-next'
git bisect good 4ef58ee18a654b1992d00281501d6eff051a0c5e
# good: [f729d8d9628d4093675abfd62d8d3a06d3d11732] drm/tinydrm: Move tinydrm_machine_little_endian()
git bisect good f729d8d9628d4093675abfd62d8d3a06d3d11732
# bad: [178e5f3a5bc1d67d1248a74c0abab41040abe7c4] drm/crc-debugfs: Add notes about CRC<->commit interactions
git bisect bad 178e5f3a5bc1d67d1248a74c0abab41040abe7c4
# good: [0486ad20e73d03c82208b802ac41e80b942b23f6] drm/rockchip: Make analogix_dp_atomic_check static
git bisect good 0486ad20e73d03c82208b802ac41e80b942b23f6
# bad: [92cb3e5980638a37c56091e605aa837d0af05a9d] dma-buf: fix stack corruption in dma_fence_chain_release
git bisect bad 92cb3e5980638a37c56091e605aa837d0af05a9d
# good: [350fd554ee44325661d0d3c3831f428f4fbb0f2d] drm/ast: Provide ddc symlink in connector sysfs directory
git bisect good 350fd554ee44325661d0d3c3831f428f4fbb0f2d
# bad: [28ba1b1da49a20ba8fb767d6ddd7c521ec79a119] drm: mali-dp: Mark expected switch fall-through
git bisect bad 28ba1b1da49a20ba8fb767d6ddd7c521ec79a119
# bad: [5b50fa2b35a4ddad11cb3d06231bf71759b49566] drm/amdgpu: Provide ddc symlink in connector sysfs directory
git bisect bad 5b50fa2b35a4ddad11cb3d06231bf71759b49566
# bad: [9ebc4d2140adcdea2399b42d3f0d2f7e141ac1a8] drm/bridge: dw-hdmi: Provide ddc symlink in connector sysfs directory
git bisect bad 9ebc4d2140adcdea2399b42d3f0d2f7e141ac1a8
# bad: [a4f9087e85de141e4e6d21ac2c583ae096cc9aba] drm/bridge: dumb-vga-dac: Provide ddc symlink in connector sysfs directory
git bisect bad a4f9087e85de141e4e6d21ac2c583ae096cc9aba
# first bad commit: [a4f9087e85de141e4e6d21ac2c583ae096cc9aba] drm/bridge: dumb-vga-dac: Provide ddc symlink in connector sysfs directory
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