[PATCH] RDMA: remove null check after call container_of()

[PATCH] RDMA: remove null check after call container_of()

[Haowen Bai]

container_of() will never return NULL, so remove useless code.

Signed-off-by: Haowen Bai <baihaowen@meizu.com>
---
 drivers/infiniband/sw/rdmavt/vt.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/infiniband/sw/rdmavt/vt.c b/drivers/infiniband/sw/rdmavt/vt.c
index 59481ae39505..b2d83b4958fc 100644
--- a/drivers/infiniband/sw/rdmavt/vt.c
+++ b/drivers/infiniband/sw/rdmavt/vt.c
@@ -50,8 +50,6 @@ struct rvt_dev_info *rvt_alloc_device(size_t size, int nports)
 	struct rvt_dev_info *rdi;
 
 	rdi = container_of(_ib_alloc_device(size), struct rvt_dev_info, ibdev);
-	if (!rdi)
-		return rdi;
 
 	rdi->ports = kcalloc(nports, sizeof(*rdi->ports), GFP_KERNEL);
 	if (!rdi->ports)
-- 
2.7.4

Re: [PATCH] RDMA: remove null check after call container_of()

[Jason Gunthorpe]

On Tue, May 17, 2022 at 09:33:28AM +0800, Haowen Bai wrote:
> container_of() will never return NULL, so remove useless code.

It is confusing here, but it can be null. If you want to do this then
you have to split out the _ib_alloc_device call and check it
seperately.

Jason

Re: [PATCH] RDMA: remove null check after call container_of()

[Christophe JAILLET]

Le 17/05/2022 à 14:16, Jason Gunthorpe a écrit :
> On Tue, May 17, 2022 at 09:33:28AM +0800, Haowen Bai wrote:
>> container_of() will never return NULL, so remove useless code.
> 
> It is confusing here, but it can be null. 

Hi,

out of curiosity, can you elaborate how it can be NULL?

CJ

> If you want to do this then
> you have to split out the _ib_alloc_device call and check it
> seperately.
> 
> Jason
> 

Re: [PATCH] RDMA: remove null check after call container_of()

[Jason Gunthorpe]

On Tue, May 17, 2022 at 07:54:38PM +0200, Christophe JAILLET wrote:
> Le 17/05/2022 à 14:16, Jason Gunthorpe a écrit :
> > On Tue, May 17, 2022 at 09:33:28AM +0800, Haowen Bai wrote:
> > > container_of() will never return NULL, so remove useless code.
> > 
> > It is confusing here, but it can be null.
> 
> Hi,
> 
> out of curiosity, can you elaborate how it can be NULL?

It is guarented/required that that container_of is a 0 offset. The
normal usage of the ib_alloc_device macro:

#define ib_alloc_device(drv_struct, member)                                    \
	container_of(_ib_alloc_device(sizeof(struct drv_struct) +              \
				      BUILD_BUG_ON_ZERO(offsetof(              \
					      struct drv_struct, member))),    \
		     struct drv_struct, member)

Enforces this property with a BUILD_BUG_ON

So, if the input pointer to container_of is reliably NULL or ERR_PTR
then the output pointer will be the same.

The rvt code here open codes the call because it is a mid-layer and
the sizeof() calculation above is not correct for it.

Jason

Re: [PATCH] RDMA: remove null check after call container_of()

[Christophe JAILLET]

Le 17/05/2022 à 20:03, Jason Gunthorpe a écrit :
> On Tue, May 17, 2022 at 07:54:38PM +0200, Christophe JAILLET wrote:
>> Le 17/05/2022 à 14:16, Jason Gunthorpe a écrit :
>>> On Tue, May 17, 2022 at 09:33:28AM +0800, Haowen Bai wrote:
>>>> container_of() will never return NULL, so remove useless code.
>>>
>>> It is confusing here, but it can be null.
>>
>> Hi,
>>
>> out of curiosity, can you elaborate how it can be NULL?
> 
> It is guarented/required that that container_of is a 0 offset. The
> normal usage of the ib_alloc_device macro:
> 
> #define ib_alloc_device(drv_struct, member)                                    \
> 	container_of(_ib_alloc_device(sizeof(struct drv_struct) +              \
> 				      BUILD_BUG_ON_ZERO(offsetof(              \
> 					      struct drv_struct, member))),    \
> 		     struct drv_struct, member)
> 
> Enforces this property with a BUILD_BUG_ON
> 
> So, if the input pointer to container_of is reliably NULL or ERR_PTR
> then the output pointer will be the same.
> 
> The rvt code here open codes the call because it is a mid-layer and
> the sizeof() calculation above is not correct for it.
> 
> Jason
> 

Crystal clear.
Thank you for the explanation.

CJ

Re: [PATCH] RDMA: remove null check after call container_of()

[baihaowen]

在 2022/5/18 上午2:03, Jason Gunthorpe 写道:
> On Tue, May 17, 2022 at 07:54:38PM +0200, Christophe JAILLET wrote:
>> Le 17/05/2022 à 14:16, Jason Gunthorpe a écrit :
>>> On Tue, May 17, 2022 at 09:33:28AM +0800, Haowen Bai wrote:
>>>> container_of() will never return NULL, so remove useless code.
>>> It is confusing here, but it can be null.
>> Hi,
>>
>> out of curiosity, can you elaborate how it can be NULL?
> It is guarented/required that that container_of is a 0 offset. The
> normal usage of the ib_alloc_device macro:
>
> #define ib_alloc_device(drv_struct, member)                                    \
> 	container_of(_ib_alloc_device(sizeof(struct drv_struct) +              \
> 				      BUILD_BUG_ON_ZERO(offsetof(              \
> 					      struct drv_struct, member))),    \
> 		     struct drv_struct, member)
>
> Enforces this property with a BUILD_BUG_ON
>
> So, if the input pointer to container_of is reliably NULL or ERR_PTR
> then the output pointer will be the same.
>
> The rvt code here open codes the call because it is a mid-layer and
> the sizeof() calculation above is not correct for it.
>
> Jason
Thank you for the explanation.   : )

-- 
Haowen Bai