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

[Toke Høiland-Jørgensen <toke@redhat.com>]

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+Paul - any idea why unrcu_pointer() isn't working here?

-Toke

> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
> head:   a196fa78a26571359740f701cf30d774eb8a72cb
> commit: 782347b6bcad07ddb574422e01e22c92e05928c8 [15/30] xdp: Add proper __rcu annotations to redirect map entries
> config: ia64-allmodconfig (attached as .config)
> compiler: ia64-linux-gcc (GCC) 9.3.0
> reproduce:
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # apt-get install sparse
>         # sparse version: v0.6.3-341-g8af24329-dirty
>         # https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/commit/?id=782347b6bcad07ddb574422e01e22c92e05928c8
>         git remote add bpf-next https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git
>         git fetch --no-tags bpf-next master
>         git checkout 782347b6bcad07ddb574422e01e22c92e05928c8
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' W=1 ARCH=ia64 
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
>
>
> sparse warnings: (new ones prefixed by >>)
>    kernel/bpf/devmap.c:561:29: sparse: sparse: incorrect type in assignment (different address spaces) @@     expected struct bpf_dtab_netdev *dst @@     got struct bpf_dtab_netdev [noderef] __rcu * @@
>    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: sparse: incorrect type in assignment (different address spaces) @@     expected struct bpf_dtab_netdev *dst @@     got struct bpf_dtab_netdev [noderef] __rcu * @@
>    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: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>>> kernel/bpf/devmap.c:1030:40: sparse: sparse: cast removes address space '__rcu' of expression
>
> vim +/__rcu +1030 kernel/bpf/devmap.c
>
>    990	
>    991	static int dev_map_notification(struct notifier_block *notifier,
>    992					ulong event, void *ptr)
>    993	{
>    994		struct net_device *netdev = netdev_notifier_info_to_dev(ptr);
>    995		struct bpf_dtab *dtab;
>    996		int i, cpu;
>    997	
>    998		switch (event) {
>    999		case NETDEV_REGISTER:
>   1000			if (!netdev->netdev_ops->ndo_xdp_xmit || netdev->xdp_bulkq)
>   1001				break;
>   1002	
>   1003			/* will be freed in free_netdev() */
>   1004			netdev->xdp_bulkq = alloc_percpu(struct xdp_dev_bulk_queue);
>   1005			if (!netdev->xdp_bulkq)
>   1006				return NOTIFY_BAD;
>   1007	
>   1008			for_each_possible_cpu(cpu)
>   1009				per_cpu_ptr(netdev->xdp_bulkq, cpu)->dev = netdev;
>   1010			break;
>   1011		case NETDEV_UNREGISTER:
>   1012			/* This rcu_read_lock/unlock pair is needed because
>   1013			 * dev_map_list is an RCU list AND to ensure a delete
>   1014			 * operation does not free a netdev_map entry while we
>   1015			 * are comparing it against the netdev being unregistered.
>   1016			 */
>   1017			rcu_read_lock();
>   1018			list_for_each_entry_rcu(dtab, &dev_map_list, list) {
>   1019				if (dtab->map.map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
>   1020					dev_map_hash_remove_netdev(dtab, netdev);
>   1021					continue;
>   1022				}
>   1023	
>   1024				for (i = 0; i < dtab->map.max_entries; i++) {
>   1025					struct bpf_dtab_netdev *dev, *odev;
>   1026	
>   1027					dev = rcu_dereference(dtab->netdev_map[i]);
>   1028					if (!dev || netdev != dev->dev)
>   1029						continue;
>> 1030					odev = unrcu_pointer(cmpxchg(&dtab->netdev_map[i], RCU_INITIALIZER(dev), NULL));
>   1031					if (dev == odev)
>   1032						call_rcu(&dev->rcu,
>   1033							 __dev_map_entry_free);
>   1034				}
>   1035			}
>   1036			rcu_read_unlock();
>   1037			break;
>   1038		default:
>   1039			break;
>   1040		}
>   1041		return NOTIFY_OK;
>   1042	}
>   1043	
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org