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

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Message-ID: <21094d57-c64e-ea7e-426e-997cd45d4635@amd.com>
Date:   Sun, 21 Jun 2020 23:38:39 +0200
From:   Nirmoy <nirmodas@....com>
To:     Dan Carpenter <dan.carpenter@...cle.com>,
        Colin King <colin.king@...onical.com>
Cc:     David Airlie <airlied@...ux.ie>, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH][next] drm/mm/selftests: fix unsigned comparison with less
 than zero


On 6/18/20 12:39 PM, Dan Carpenter wrote:
> On Wed, Jun 17, 2020 at 04:59:59PM +0100, Colin King wrote:
>> 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>
>> ---
>>   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;
> The error codes in this function seem pretty messed up.
>
> Speaking of error codes, what the heck is going on with
> prepare_igt_frag().


This is on me. I will send a patch to correct this mistake.


Thanks,

Nirmoy


>
>    1037  static int prepare_igt_frag(struct drm_mm *mm,
>    1038                              struct drm_mm_node *nodes,
>    1039                              unsigned int num_insert,
>    1040                              const struct insert_mode *mode)
>    1041  {
>    1042          unsigned int size = 4096;
>    1043          unsigned int i;
>    1044          u64 ret = -EINVAL;
>                  ^^^^^^^^^^^^^^^^^^
> Why is it u64?
>
>    1045
>    1046          for (i = 0; i < num_insert; i++) {
>    1047                  if (!expect_insert(mm, &nodes[i], size, 0, i,
>    1048                                     mode) != 0) {
>    1049                          pr_err("%s insert failed\n", mode->name);
>    1050                          goto out;
>                                  ^^^^^^^^
> One of the common bugs with do nothing gotos is that we forget to set
> the error code.  If we did a direct "return -EINVAL;" here, then there
> would be no ambiguity.
>
>    1051                  }
>    1052          }
>    1053
>    1054          /* introduce fragmentation by freeing every other node */
>    1055          for (i = 0; i < num_insert; i++) {
>    1056                  if (i % 2 == 0)
>    1057                          drm_mm_remove_node(&nodes[i]);
>    1058          }
>    1059
>    1060  out:
>    1061          return ret;
>    1062
>    1063  }
>
> regards,
> dan carpenter
>
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