Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx> writes:
> When saving BOs in the hang state we skip one entry of the
> kernel_state->bo[] array, thus leaving it to NULL. This leads to a NULL
> pointer dereference when, later in this function, we iterate over all
> BOs to check their ->madv state.
>
> Fixes: ca26d28bbaa3 ("drm/vc4: improve throughput by pipelining binning and rendering jobs")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/vc4/vc4_gem.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_gem.c b/drivers/gpu/drm/vc4/vc4_gem.c
> index 6c32c89a83a9..19ac7fe0e5db 100644
> --- a/drivers/gpu/drm/vc4/vc4_gem.c
> +++ b/drivers/gpu/drm/vc4/vc4_gem.c
> @@ -208,7 +208,7 @@ vc4_save_hang_state(struct drm_device *dev)
> kernel_state->bo[j + prev_idx] = &bo->base.base;
> j++;
> }
> - prev_idx = j + 1;
> + prev_idx = j;
Could we replace the whole "[j + prev_idx]" with a "[k++]" and maybe a
WARN_ON_ONCE(k != state->bo_count) at the end?
I really need to figure out if I can come up with a way to make IGT
cases for GPU hangs on vc4, despite the validation. I found a bug in
GPU reset due to BCL hangs when doing vc5, but I don't have a testcase.
Maybe some submit flags that overwrite the BCL or RCL to do an infinite
loop?
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