[igt-dev] [PATCH i-g-t 2/2] i915/gem_mmap_offset: Avoid FPE in calculating npages to clear

[Kamil Konieczny]

On 2023-01-11 at 11:26:33 +0100, Zbigniew Kempczyński wrote:
> Add a small delay (ala gem_create/clear) to busywait when we run out of
> pages to allocate, avoid the FPE and continue on a bit later once the
> other threads have released some pages of their own.
> 
> Fixes: https://gitlab.freedesktop.org/drm/intel/-/issues/7788
> 
> Signed-off-by: Chris Wilson <chris.p.wilson at linux.intel.com>
> Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>

Reviewed-by: Kamil Konieczny <kamil.konieczny at linux.intel.com>

> ---
>  tests/i915/gem_mmap_offset.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/tests/i915/gem_mmap_offset.c b/tests/i915/gem_mmap_offset.c
> index b38b7edae3..962fc1b739 100644
> --- a/tests/i915/gem_mmap_offset.c
> +++ b/tests/i915/gem_mmap_offset.c
> @@ -673,8 +673,13 @@ static uint64_t get_npages(_Atomic(uint64_t) *global, uint64_t npages)
>  
>  	max = *global;
>  	do {
> +		while (max < 16) {
> +			usleep(10);
> +			max = *global;
> +		}
> +
>  		old = max;
> -		try = 1 + npages % (max / 2);
> +		try = 1 + npages % (max / 2 - 1);
>  		max -= try;
>  	} while ((max = atomic_compare_swap_u64(global, old, max)) != old);
>  
> -- 
> 2.34.1
>