[PATCH v2] drm/amdgpu: fix fdinfo race with process exit

[Felix Kuehling]

Am 2021-07-29 um 10:13 p.m. schrieb Philip Yang:
> Get process vm root BO ref in case process is exiting and root BO is
> freed, to avoid NULL pointer dereference backtrace:
>
> BUG: unable to handle kernel NULL pointer dereference at
> 0000000000000000
> Call Trace:
> amdgpu_show_fdinfo+0xfe/0x2a0 [amdgpu]
> seq_show+0x12c/0x180
> seq_read+0x153/0x410
> vfs_read+0x91/0x140[ 3427.206183]  ksys_read+0x4f/0xb0
> do_syscall_64+0x5b/0x1a0
> entry_SYSCALL_64_after_hwframe+0x65/0xca
>
> v2: rebase to staging
>
> Signed-off-by: Philip Yang <Philip.Yang at amd.com>

The patch is

Reviewed-by: Felix Kuehling <Felix.Kuehling at amd.com>


> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_fdinfo.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fdinfo.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_fdinfo.c
> index d94c5419ec25..5a6857c44bb6 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fdinfo.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fdinfo.c
> @@ -59,6 +59,7 @@ void amdgpu_show_fdinfo(struct seq_file *m, struct file *f)
>  	uint64_t vram_mem = 0, gtt_mem = 0, cpu_mem = 0;
>  	struct drm_file *file = f->private_data;
>  	struct amdgpu_device *adev = drm_to_adev(file->minor->dev);
> +	struct amdgpu_bo *root;
>  	int ret;
>  
>  	ret = amdgpu_file_to_fpriv(f, &fpriv);
> @@ -69,13 +70,19 @@ void amdgpu_show_fdinfo(struct seq_file *m, struct file *f)
>  	dev = PCI_SLOT(adev->pdev->devfn);
>  	fn = PCI_FUNC(adev->pdev->devfn);
>  
> -	ret = amdgpu_bo_reserve(fpriv->vm.root.bo, false);
> +	root = amdgpu_bo_ref(fpriv->vm.root.bo);
> +	if (!root)
> +		return;
> +
> +	ret = amdgpu_bo_reserve(root, false);
>  	if (ret) {
>  		DRM_ERROR("Fail to reserve bo\n");
>  		return;
>  	}
>  	amdgpu_vm_get_memory(&fpriv->vm, &vram_mem, &gtt_mem, &cpu_mem);
> -	amdgpu_bo_unreserve(fpriv->vm.root.bo);
> +	amdgpu_bo_unreserve(root);
> +	amdgpu_bo_unref(&root);
> +
>  	seq_printf(m, "pdev:\t%04x:%02x:%02x.%d\npasid:\t%u\n", domain, bus,
>  			dev, fn, fpriv->vm.pasid);
>  	seq_printf(m, "vram mem:\t%llu kB\n", vram_mem/1024UL);