| Message ID | 1652751208-23211-1-git-send-email-baihaowen@meizu.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Jason Gunthorpe |
| Headers | show |
| Series | RDMA: remove null check after call container_of() | expand |
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
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 >
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
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
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. : )
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)
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(-)