dependencyOn 2021/4/15 11:35, zhudi wrote:
> From: Di Zhu <[email protected]>
>
> We encountered a crash: in the packet receiving process, we got an
> illegal VLAN device address, but the VLAN device address saved in vmcore
> is correct. After checking the code, we found a possible data
> competition:
> CPU 0: CPU 1:
> (RCU read lock) (RTNL lock)
> vlan_do_receive() register_vlan_dev()
> vlan_find_dev()
>
> ->__vlan_group_get_device() ->vlan_group_prealloc_vid()
>
> In vlan_group_prealloc_vid(), We need to make sure that kzalloc is
> executed before assigning a value to vlan devices array, otherwise we
As my understanding, there is a dependency between calling kzalloc() and
assigning the address(returned from kzalloc()) to vg->vlan_devices_arrays,
CPU and compiler can see the dependency, why can't it handling the
dependency before adding the smp_wmb()?
See CONTROL DEPENDENCIES section in Documentation/memory-barriers.txt:
However, stores are not speculated. This means that ordering -is- provided
for load-store control dependencies, as in the following example:
q = READ_ONCE(a);
if (q) {
WRITE_ONCE(b, 1);
}
> may get a wrong address from the hardware cache on another cpu.
>
> So fix it by adding memory barrier instruction to ensure the order
> of memory operations.
>
> Signed-off-by: Di Zhu <[email protected]>
> ---
> net/8021q/vlan.c | 2 ++
> net/8021q/vlan.h | 3 +++
> 2 files changed, 5 insertions(+)
>
> diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
> index 8b644113715e..4f541e05cd3f 100644
> --- a/net/8021q/vlan.c
> +++ b/net/8021q/vlan.c
> @@ -71,6 +71,8 @@ static int vlan_group_prealloc_vid(struct vlan_group *vg,
> if (array == NULL)
> return -ENOBUFS;
>
> + smp_wmb();
> +
> vg->vlan_devices_arrays[pidx][vidx] = array;
> return 0;
> }
> diff --git a/net/8021q/vlan.h b/net/8021q/vlan.h
> index 953405362795..7408fda084d3 100644
> --- a/net/8021q/vlan.h
> +++ b/net/8021q/vlan.h
> @@ -57,6 +57,9 @@ static inline struct net_device
> *__vlan_group_get_device(struct vlan_group *vg,
>
> array = vg->vlan_devices_arrays[pidx]
> [vlan_id / VLAN_GROUP_ARRAY_PART_LEN];
> +
> + smp_rmb();
> +
> return array ? array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN] : NULL;
> }
>
>
