Re: [PATCH v7 1/6] drm/amdgpu: Fix init ordering in amdgpu_vram_mgr_init()

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Fri, 2026-07-03 at 15:08 +0200, Christian König wrote:
> Arun please take a look at this.
> 
> Thanks,
> Christian.

FWIW Sashiko claims there is yet another pre-existing bug WRT ordering
here, but since the fix wasn't needed for the rest of the series, I
focused on this one.

Thanks,
Thomas


> 
> On 7/3/26 15:05, Thomas Hellström wrote:
> > drmm_cgroup_register_region() is called before INIT_LIST_HEAD() and
> > gpu_buddy_init() in amdgpu_vram_mgr_init(). If it fails, the
> > function
> > returns early and bypasses those initializations.
> > 
> > Since adev->mman.initialized is set to true before
> > amdgpu_vram_mgr_init()
> > is called, a failure triggers amdgpu_ttm_fini(), which calls
> > amdgpu_vram_mgr_fini(), which then:
> > 
> >  - Calls list_for_each_entry_safe() on reservations_pending and
> >    reserved_pages, whose list_head::next pointers are zero-
> > initialized
> >    (NULL). The loop does not recognize them as empty and
> > dereferences NULL.
> > 
> >  - Calls gpu_buddy_fini(), which iterates free_trees[]
> > unconditionally
> >    via for_each_free_tree(). Since mm->free_trees is NULL
> >    (never allocated), this dereferences NULL.
> > 
> > Both result in a kernel panic on the module load error path.
> > 
> > Fix by moving drmm_cgroup_register_region() to after the list and
> > buddy
> > allocator are fully initialized, so the teardown path is safe to
> > run.
> > 
> > Reported-by: Sashiko-bot <sashiko-bot@kernel.org>
> > Closes:
> > https://sashiko.dev/#/patchset/20260428073116.15687-1-thomas.hellstrom@linux.intel.com?part=4
> > Fixes: 2b624a2c1865 ("drm/ttm: Handle cgroup based eviction in
> > TTM")
> > Cc: Friedrich Vock <friedrich.vock@gmx.de>
> > Cc: Maarten Lankhorst <dev@lankhorst.se>
> > Cc: Tejun Heo <tj@kernel.org>
> > Cc: Maxime Ripard <mripard@kernel.org>
> > Cc: Christian König <christian.koenig@amd.com>
> > Cc: Alex Deucher <alexander.deucher@amd.com>
> > Cc: amd-gfx@lists.freedesktop.org
> > Cc: dri-devel@lists.freedesktop.org
> > Cc: <stable@vger.kernel.org> # v6.14+
> > Assisted-by: GitHub_Copilot:claude-sonnet-4.6
> > Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> > ---
> >  drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
> > b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
> > index 2a241a5b12c4..ac3f71d77140 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
> > @@ -918,9 +918,6 @@ int amdgpu_vram_mgr_init(struct amdgpu_device
> > *adev)
> >  	struct ttm_resource_manager *man = &mgr->manager;
> >  	int err;
> >  
> > -	man->cg = drmm_cgroup_register_region(adev_to_drm(adev),
> > "vram", adev->gmc.real_vram_size);
> > -	if (IS_ERR(man->cg))
> > -		return PTR_ERR(man->cg);
> >  	ttm_resource_manager_init(man, &adev->mman.bdev,
> >  				  adev->gmc.real_vram_size);
> >  
> > @@ -935,6 +932,10 @@ int amdgpu_vram_mgr_init(struct amdgpu_device
> > *adev)
> >  	if (err)
> >  		return err;
> >  
> > +	man->cg = drmm_cgroup_register_region(adev_to_drm(adev),
> > "vram", adev->gmc.real_vram_size);
> > +	if (IS_ERR(man->cg))
> > +		return PTR_ERR(man->cg);
> > +
> >  	ttm_set_driver_manager(&adev->mman.bdev, TTM_PL_VRAM,
> > &mgr->manager);
> >  	ttm_resource_manager_set_used(man, true);
> >  	return 0;