2021-11-16 01:58:37

by 赵军奎

Subject: [PATCH] drm/tegra: remove no need NULL check before kfree

This change is to cleanup the code a bit.

Signed-off-by: Bernard Zhao <[email protected]>
---
drivers/gpu/drm/tegra/submit.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/tegra/submit.c b/drivers/gpu/drm/tegra/submit.c
index 776f825df52f..c2fc9677742e 100644
--- a/drivers/gpu/drm/tegra/submit.c
+++ b/drivers/gpu/drm/tegra/submit.c
@@ -608,12 +608,10 @@ int tegra_drm_ioctl_channel_submit(struct drm_device *drm, void *data,
if (job_data && job_data->used_mappings) {
for (i = 0; i < job_data->num_used_mappings; i++)
tegra_drm_mapping_put(job_data->used_mappings[i].mapping);
-
- kfree(job_data->used_mappings);
}

- if (job_data)
- kfree(job_data);
+ kfree(job_data->used_mappings);
+ kfree(job_data);
put_bo:
gather_bo_put(&bo->base);
unlock:
--
2.33.1

2021-11-16 10:01:27

by Mikko Perttunen

Subject: Re: [PATCH] drm/tegra: remove no need NULL check before kfree

On 11/16/21 3:55 AM, Bernard Zhao wrote:
> This change is to cleanup the code a bit.
>
> Signed-off-by: Bernard Zhao <[email protected]>
> ---
> drivers/gpu/drm/tegra/submit.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/tegra/submit.c b/drivers/gpu/drm/tegra/submit.c
> index 776f825df52f..c2fc9677742e 100644
> --- a/drivers/gpu/drm/tegra/submit.c
> +++ b/drivers/gpu/drm/tegra/submit.c
> @@ -608,12 +608,10 @@ int tegra_drm_ioctl_channel_submit(struct drm_device *drm, void *data,
> if (job_data && job_data->used_mappings) {
> for (i = 0; i < job_data->num_used_mappings; i++)
> tegra_drm_mapping_put(job_data->used_mappings[i].mapping);
> -
> - kfree(job_data->used_mappings);
> }
>
> - if (job_data)
> - kfree(job_data);
> + kfree(job_data->used_mappings);

Now if job_data == NULL, we dereference a NULL pointer here.

In general I'm not a fan of relying on kfree() etc. being a no-op on
NULL pointers, since doing so gets rid of visual hints on code paths
indicating the "liveness" of pointer variables.

However I'll let Thierry/other maintainers decide according to their
preferences.

Thanks,
Mikko

> + kfree(job_data);
> put_bo:
> gather_bo_put(&bo->base);
> unlock:
>