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

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Message-ID: <83ec451a-ceaa-5d62-948e-c34bbd670c0e@canonical.com>
Date:   Thu, 17 Aug 2017 23:16:47 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Ilia Mirkin <imirkin@...m.mit.edu>
Cc:     Ben Skeggs <bskeggs@...hat.com>, David Airlie <airlied@...ux.ie>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
        kernel-janitors@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][V2] drm/nouveau: perform null check on msto[i] rathern
 than msto

On 17/08/17 23:07, Ilia Mirkin wrote:
> On Thu, Aug 17, 2017 at 6:03 PM, Colin King <colin.king@...onical.com> wrote:
>> From: Colin Ian King <colin.king@...onical.com>
>>
>> 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@...onical.com>
>> ---
>>  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.


> 
>>                 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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