linux-kernel - Re: [PATCH v3] drm/panthor: Fix couple of NULL vs IS

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Message-ID: <20240402163838.34003a10@collabora.com>
Date: Tue, 2 Apr 2024 16:38:38 +0200
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
Cc: Steven Price <steven.price@....com>, Liviu Dudau <liviu.dudau@....com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
 <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, Heiko Stuebner
 <heiko@...ech.de>, Grant Likely <grant.likely@...aro.org>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 dan.carpenter@...aro.org, kernel-janitors@...r.kernel.org,
 error27@...il.com
Subject: Re: [PATCH v3] drm/panthor: Fix couple of NULL vs IS_ERR() bugs

On Tue,  2 Apr 2024 07:14:11 -0700
Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com> wrote:

> Currently panthor_vm_get_heap_pool() returns both ERR_PTR() and
> NULL(when create is false and if there is no poool attached to the

                                               ^ pool

> VM)
> 	- Change the function to return error pointers, when pool is
> 	  NULL return -ENOENT
> 	- Also handle the callers to check for IS_ERR() on failure.
> 
> Fixes: 4bdca1150792 ("drm/panthor: Add the driver frontend block")

I would explain that the code was correct, but the documentation didn't
match the function behavior, otherwise it feels a bit weird to have a
Fixes tag here.

> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
> ---
> This is spotted by smatch and the patch is only compile tested
> 
> v1->v2: Fix the function panthor_vm_get_heap_pool() to only return error
> pointers and handle the caller sites [Suggested by Boris Brezillon]
>         - Also merge these IS_ERR() vs NULL bugs into same patch
> 
> v2->v3: pull out error checking for devm_drm_dev_alloc() failure.
> ---
>  drivers/gpu/drm/panthor/panthor_drv.c   | 4 ++--
>  drivers/gpu/drm/panthor/panthor_mmu.c   | 2 ++
>  drivers/gpu/drm/panthor/panthor_sched.c | 2 +-
>  3 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
> index 11b3ccd58f85..050b905b0453 100644
> --- a/drivers/gpu/drm/panthor/panthor_drv.c
> +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> @@ -1090,8 +1090,8 @@ static int panthor_ioctl_tiler_heap_destroy(struct drm_device *ddev, void *data,
>  		return -EINVAL;
>  
>  	pool = panthor_vm_get_heap_pool(vm, false);
> -	if (!pool) {
> -		ret = -EINVAL;
> +	if (IS_ERR(pool)) {
> +		ret = PTR_ERR(pool);
>  		goto out_put_vm;
>  	}
>  
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> index fdd35249169f..e1285cdb09ff 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -1893,6 +1893,8 @@ struct panthor_heap_pool *panthor_vm_get_heap_pool(struct panthor_vm *vm, bool c
>  			vm->heaps.pool = panthor_heap_pool_get(pool);
>  	} else {
>  		pool = panthor_heap_pool_get(vm->heaps.pool);
> +		if (!pool)
> +			pool = ERR_PTR(-ENOENT);
>  	}
>  	mutex_unlock(&vm->heaps.lock);
>  
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> index 5f7803b6fc48..617df2b980d0 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.c
> +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> @@ -1343,7 +1343,7 @@ static int group_process_tiler_oom(struct panthor_group *group, u32 cs_id)
>  	if (unlikely(csg_id < 0))
>  		return 0;
>  
> -	if (!heaps || frag_end > vt_end || vt_end >= vt_start) {
> +	if (IS_ERR(heaps) || frag_end > vt_end || vt_end >= vt_start) {
>  		ret = -EINVAL;
>  	} else {
>  		/* We do the allocation without holding the scheduler lock to avoid