linux-kernel - Re: [PATCH] drm/tegra: submit: No need for Null pointer check before kfree

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Date:   Wed, 28 Dec 2022 18:38:48 +0530
From:   Deepak R Varma <drv@...lo.com>
To:     Mikko Perttunen <cyndis@...si.fi>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Jonathan Hunter <jonathanh@...dia.com>,
        dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Saurabh Singh Sengar <ssengar@...rosoft.com>,
        Praveen Kumar <kumarpraveen@...ux.microsoft.com>,
        Deepak R Varma <drv@...lo.com>
Subject: Re: [PATCH] drm/tegra: submit: No need for Null pointer check before
 kfree

On Wed, Dec 28, 2022 at 02:28:54PM +0200, Mikko Perttunen wrote:
> On 12/27/22 19:14, Deepak R Varma wrote:
> > kfree() & vfree() internally perform NULL check on the pointer handed
> > to it and take no action if it indeed is NULL. Hence there is no need
> > for a pre-check of the memory pointer before handing it to
> > kfree()/vfree().
> >
> > Issue reported by ifnullfree.cocci Coccinelle semantic patch script.
> >
> > Signed-off-by: Deepak R Varma <drv@...lo.com>
> > ---
> >   drivers/gpu/drm/tegra/submit.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/tegra/submit.c b/drivers/gpu/drm/tegra/submit.c
> > index 066f88564169..06f836db99d0 100644
> > --- a/drivers/gpu/drm/tegra/submit.c
> > +++ b/drivers/gpu/drm/tegra/submit.c
> > @@ -680,8 +680,8 @@ int tegra_drm_ioctl_channel_submit(struct drm_device *drm, void *data,
> >   		kfree(job_data->used_mappings);
> >   	}
> >
> > -	if (job_data)
> > -		kfree(job_data);
> > +	kfree(job_data);
> > +
> >   put_bo:
> >   	gather_bo_put(&bo->base);
> >   unlock:
> > --
> > 2.34.1
> >
> >
> >
>
> It continues to be the case that I think this transform is bad. Same applies
> to the host1x patch.

Hello Mikko,
Thank you for responding to the patch proposal. Could you please explain why is
this bad?

Regards,
./drv

>
> Mikko