linux-kernel - BUG: amdgpu: NULL pointer dereference introduced in 5.9-rc1

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Message-ID: <ghmu1758gs.fsf@gouders.net>
Date:   Wed, 30 Sep 2020 22:13:23 +0200
From:   Dirk Gouders <dirk@...ders.net>
To:     Alex Deucher <alexander.deucher@....com>
Cc:     amd-gfx@...ts.freedesktop.org,
        Hawking Zhang <Hawking.Zhang@....com>,
        Evan Quan <evan.quan@....com>
Subject: BUG: amdgpu: NULL pointer dereference introduced in 5.9-rc1

Commit c1cf79ca5ced46 (drm/amdgpu: use IP discovery table for renoir)
introduced a NULL pointer dereference when booting with
amdgpu.discovery=0.

For amdgpu.discovery=0 that commit effectively removed the call of
vega10_reg_base_init(adev), so I tested the correctness of the bisect
session by restoring that function call for amdgpu_discovery == 0 and with
that change, the NULL pointer dereference does not occur:

diff --git a/drivers/gpu/drm/amd/amdgpu/soc15.c b/drivers/gpu/drm/amd/amdgpu/soc15.c
index 84d811b6e48b..2e93c5e1e7e6 100644
--- a/drivers/gpu/drm/amd/amdgpu/soc15.c
+++ b/drivers/gpu/drm/amd/amdgpu/soc15.c
@@ -699,7 +699,8 @@ static void soc15_reg_base_init(struct amdgpu_device *adev)
                                         "fallback to legacy init method\n");
                                vega10_reg_base_init(adev);
                        }
-               }
+               } else
+                       vega10_reg_base_init(adev);
                break;
        case CHIP_VEGA20:
                vega20_reg_base_init(adev);

Dirk