livepatch: Traverse klp_func_list by using the rcu interface

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5CJ7X



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klp_find_func_node() is used to traverse the klp_func_list linked list.
Currently, klp_find_func_node() is used only when the klp_mutex lock is
held. In the subsequent submission, we need to access the klp_func_list
linked list in the exception handling process and cannot hold the
klp_mutex lock.

We change the traversal of klp_func_list to use the rcu interface and
perform rcu synchronization when deleting nodes.

Signed-off-by: Li Huafei <lihuafei1@huawei.com>
Reviewed-by: Xu Kuohai <xukuohai@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>