Re: [Nouveau] [PATCH][V2] drm/nouveau: perform null check on msto[i] rathern than msto

[Ben Skeggs]

On 08/18/2017 08:20 AM, Ben Skeggs wrote:
> On 08/18/2017 08:16 AM, Colin Ian King wrote:
>> On 17/08/17 23:07, Ilia Mirkin wrote:
>>> On Thu, Aug 17, 2017 at 6:03 PM, Colin King <colin.king@xxxxxxxxxxxxx> wrote:
>>>> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>>>>
>>>> The null check on the array msto is incorrect since msto is never
>>>> null. The null check should be instead on msto[i] since this is
>>>> being dereferenced in the call to drm_mode_connector_attach_encoder.
>>>>
>>>> Thanks to Emil Velikov for pointing out the mistake in my original
>>>> fix and for suggesting the correct fix.
>>>>
>>>> Detected by CoverityScan, CID#1375915 ("Array compared against 0")
>>>>
>>>> Fixes: f479c0ba4a17 ("drm/nouveau/kms/nv50: initial support for DP 1.2 multi-stream")
>>>> Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>>>> ---
>>>>  drivers/gpu/drm/nouveau/nv50_display.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/nouveau/nv50_display.c b/drivers/gpu/drm/nouveau/nv50_display.c
>>>> index f7b4326a4641..ed444ecd9e85 100644
>>>> --- a/drivers/gpu/drm/nouveau/nv50_display.c
>>>> +++ b/drivers/gpu/drm/nouveau/nv50_display.c
>>>> @@ -3141,7 +3141,7 @@ nv50_mstc_new(struct nv50_mstm *mstm, struct drm_dp_mst_port *port,
>>>>         mstc->connector.funcs->reset(&mstc->connector);
>>>>         nouveau_conn_attach_properties(&mstc->connector);
>>>>
>>>> -       for (i = 0; i < ARRAY_SIZE(mstm->msto) && mstm->msto; i++)
>>>> +       for (i = 0; i < ARRAY_SIZE(mstm->msto) && mstm->msto[i]; i++)
>>>
>>> Ben will have to rule on which way is correct, but another
>>> interpretation is that it should be
>>>
>>> for (...; i < ARRAY_SIZE; i++)
>>>   if (mstm->msto[i])
>>>     do_stuff()
>>
>> Yes, I suspect that is a better generic solution top cope with potential
>> "holes".
>>>
>>> I haven't the faintest clue whether the msto array can have "holes" or not.
>>
>> Indeed. Let's see what Ben says.
> No, there can't be holes here.  I believe the V2 patch to be correct.
Also, I've taken the patch in my tree, and will get it to Dave at some
point.

Thank you!
Ben.

> 
> Ben.
>>
>>
>>>
>>>>                 drm_mode_connector_attach_encoder(&mstc->connector, &mstm->msto[i]->encoder);
>>>>
>>>>         drm_object_attach_property(&mstc->connector.base, dev->mode_config.path_property, 0);
>>>> --
>>>> 2.11.0
>>>>
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>>
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