linux-kernel - Re: [PATCH][next] drm/mm/selftests: fix unsigned comparison with less than zero

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Date:   Sun, 21 Jun 2020 17:33:01 +0200
From:   Christian König <christian.koenig@....com>
To:     Colin King <colin.king@...onical.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] drm/mm/selftests: fix unsigned comparison with less
 than zero

Am 17.06.20 um 17:59 schrieb Colin King:
> From: Colin Ian King <colin.king@...onical.com>
>
> Function get_insert_time can return error values that are cast
> to a u64. The checks of insert_time1 and insert_time2 check for
> the errors but because they are u64 variables the check for less
> than zero can never be true. Fix this by casting the value to s64
> to allow of the negative error check to succeed.
>
> Addresses-Coverity: ("Unsigned compared against 0, no effect")
> Fixes: 6e60d5ded06b ("drm/mm: add ig_frag selftest")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>

Reviewed-by: Christian König <christian.koenig@....com>

Going to pick that up for drm-misc-fixes tomorrow.

> ---
>   drivers/gpu/drm/selftests/test-drm_mm.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/selftests/test-drm_mm.c b/drivers/gpu/drm/selftests/test-drm_mm.c
> index 3846b0f5bae3..671a152a6df2 100644
> --- a/drivers/gpu/drm/selftests/test-drm_mm.c
> +++ b/drivers/gpu/drm/selftests/test-drm_mm.c
> @@ -1124,12 +1124,12 @@ static int igt_frag(void *ignored)
>   
>   		insert_time1 = get_insert_time(&mm, insert_size,
>   					       nodes + insert_size, mode);
> -		if (insert_time1 < 0)
> +		if ((s64)insert_time1 < 0)
>   			goto err;
>   
>   		insert_time2 = get_insert_time(&mm, (insert_size * 2),
>   					       nodes + insert_size * 2, mode);
> -		if (insert_time2 < 0)
> +		if ((s64)insert_time2 < 0)
>   			goto err;
>   
>   		pr_info("%s fragmented insert of %u and %u insertions took %llu and %llu nsecs\n",