Re: [PATCH v3] drm/panthor: Fix couple of NULL vs IS_ERR() bugs

[Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>]

Hi Boris,

On 03/04/24 12:47, Boris Brezillon wrote:
> On Tue,  2 Apr 2024 07:14:11 -0700
> Harshit Mogalapalli <harshit.m.mogalapalli@oracle.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
>> 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")
>> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
> 
> Queued to drm-misc-next with the following commit message:
> 
> "
> drm/panthor: Don't return NULL from panthor_vm_get_heap_pool()
>      
> The kernel doc says this function returns either a valid pointer
> or an ERR_PTR(), but in practice this function can return NULL if
> create=false. Fix the function to match the doc (return
> ERR_PTR(-ENOENT) instead of NULL) and adjust all call-sites
> accordingly.
> "
> 

Thanks a lot for making the change!

Regards,
Harshit

> Thanks,
> 
> Boris
> 
>> ---
>> 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
>