Re: [PATCH] gpu: drm: drm_mm: Fix a sleep-in-atomic-context bug in show_leaks()

[Chris Wilson]

Quoting Jia-Ju Bai (2018-09-01 13:20:41)
> The driver may sleep with holding a spinlock.
> 
> The function call paths (from bottom to top) in Linux-4.16 are:
> 
> [FUNC] kmalloc(GFP_KERNEL)
> drivers/gpu/drm/drm_mm.c, 130: 
>         kmalloc in show_leaks
> drivers/gpu/drm/drm_mm.c, 913: 
>         show_leaks in drm_mm_takedown
> drivers/gpu/drm/drm_vma_manager.c, 107: 
>         drm_mm_takedown in drm_vma_offset_manager_destroy
> drivers/gpu/drm/drm_vma_manager.c, 106: 
>         _raw_write_lock in drm_vma_offset_manager_destroy
> 
> [FUNC] kmalloc(GFP_KERNEL)
> drivers/gpu/drm/drm_mm.c, 130: 
>         kmalloc in show_leaks
> drivers/gpu/drm/drm_mm.c, 913: 
>         show_leaks in drm_mm_takedown
> drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c, 71: 
>         drm_mm_takedown in amdgpu_vram_mgr_fini
> drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c, 70: 
>         spin_lock in amdgpu_vram_mgr_fini
> 
> [FUNC] kmalloc(GFP_KERNEL)
> drivers/gpu/drm/drm_mm.c, 130: 
>         kmalloc in show_leaks
> drivers/gpu/drm/drm_mm.c, 913: 
>         show_leaks in drm_mm_takedown
> drivers/gpu/drm/ttm/ttm_bo_manager.c, 128: 
>         drm_mm_takedown in ttm_bo_man_takedown
> drivers/gpu/drm/ttm/ttm_bo_manager.c, 126: 
>         spin_lock in ttm_bo_man_takedown
> 
> To fix this bug, GFP_KERNEL is replaced with GFP_ATOMIC.

The bug are above, since those spinlocks do not protect the data and
imply use-after-free.
-Chris