linux-kernel - Re: [PATCH] drm/nouveau: Prevents NULL pointer dereference in nouveau_uvmm_sm

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Message-ID: <GV1PR10MB6563980A0097762C6868E2DCE8B1A@GV1PR10MB6563.EURPRD10.PROD.OUTLOOK.COM>
Date:   Wed, 15 Nov 2023 14:38:12 +0530
From:   Yuran Pereira <yuran.pereira@...mail.com>
To:     Danilo Krummrich <dakr@...hat.com>
Cc:     airlied@...il.com, kherbst@...hat.com, lyude@...hat.com,
        daniel@...ll.ch, sumit.semwal@...aro.org, christian.koenig@....com,
        dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org,
        linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH] drm/nouveau: Prevents NULL pointer dereference in
 nouveau_uvmm_sm_prepare

Hello Danilo,
On Tue, Nov 14, 2023 at 05:23:59PM +0100, Danilo Krummrich wrote:
> Hi Yuran,
> 
> op_map_prepare() can't be called with `args` being NULL, since when called
> through nouveau_uvmm_sm_unmap_prepare() we can't hit the DRM_GPUVA_OP_MAP
> case at all.
> 
> Unmapping something never leads to a new mapping being created, it can lead
> to remaps though.
> 
Yes, you're right. I certainly hadn't noticed that when I first
submitted this patch.
> 
> This check is not required for the reason given above. If you like, you
> can change this patch up to remove the args check and add a comment like:
> 
> /* args can't be NULL when called for a map operation. */
> 
Sure, I'll do that, sounds reasonable.

Thank you for your feedback.

Yuran
> 
> Yeah, I see how this unnecessary check made you think so.
> 
> - Danilo
> 
>