Re: [bpf-next:master 15/30] kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression

[Chen, Rong A <rong.a.chen@intel.com>]

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On 6/29/2021 6:53 AM, Paul E. McKenney wrote:
> On Tue, Jun 29, 2021 at 12:42:52AM +0200, Toke Høiland-Jørgensen wrote:
>> "Paul E. McKenney" <paulmck@kernel.org> writes:
>>
>>> On Sat, Jun 26, 2021 at 12:00:55PM +0200, Toke Høiland-Jørgensen wrote:
>>>> +Paul - any idea why unrcu_pointer() isn't working here?
>>>
>>> Hello, Toke!
>>>
>>> My distro version of sparse core-dumped before getting that far along.
>>>
>>> I cloned and built the latest version, and got only the following errors
>>> from kernel/bpf/devmap.c:
>>>
>>> ------------------------------------------------------------------------
>>>
>>>    CHECK   scripts/mod/empty.c
>>>    CALL    scripts/checksyscalls.sh
>>>    CALL    scripts/atomic/check-atomics.sh
>>>    DESCEND objtool
>>>    CC      kernel/bpf/devmap.o
>>>    CHECK   kernel/bpf/devmap.c
>>> kernel/bpf/devmap.c:561:29: warning: incorrect type in assignment (different address spaces)
>>> kernel/bpf/devmap.c:561:29:    expected struct bpf_dtab_netdev *dst
>>> kernel/bpf/devmap.c:561:29:    got struct bpf_dtab_netdev [noderef] __rcu *
>>> kernel/bpf/devmap.c:657:29: warning: incorrect type in assignment (different address spaces)
>>> kernel/bpf/devmap.c:657:29:    expected struct bpf_dtab_netdev *dst
>>> kernel/bpf/devmap.c:657:29:    got struct bpf_dtab_netdev [noderef] __rcu *
>>
>> Hmm, but those shouldn't be there either. Seems I missed those when
>> rebasing, will send a follow-up patch...
> 
> Just check out different versions of sparse and average the results?  ;-)
> 
> 							Thanx, Paul

Hi Paul,

I tested the original attached config with the reproduce step, and I can 
reproduce the warning:

$ COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross C=1 
CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' W=1 ARCH=ia64 kernel/bpf/
...
kernel/bpf/devmap.c:561:29: sparse: warning: incorrect type in 
assignment (different address spaces)
kernel/bpf/devmap.c:561:29: sparse:    expected struct bpf_dtab_netdev *dst
kernel/bpf/devmap.c:561:29: sparse:    got struct bpf_dtab_netdev 
[noderef] __rcu *
kernel/bpf/devmap.c:657:29: sparse: warning: incorrect type in 
assignment (different address spaces)
kernel/bpf/devmap.c:657:29: sparse:    expected struct bpf_dtab_netdev *dst
kernel/bpf/devmap.c:657:29: sparse:    got struct bpf_dtab_netdev 
[noderef] __rcu *
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression
kernel/bpf/devmap.c:1030:40: sparse: warning: cast removes address space 
'__rcu' of expression

and sparse is from latest master branch:
$ sparse --version
v0.6.3-341-g8af24329


Best Regards,
Rong Chen