Paul E. McKenney wrote:
> Notwithstanding my confusion about what your self-referential
> srcu_dereference() is intended to achieve, what happens if you change the
> "void *ptr = srcu_dereference(ptr, &srcu);" to add __rcu?
Sorry, I wrote this code for only showing warning message.
This self-referential has no intention.
Well, you can reproduce this warning with current linux.git by running
make C=1 security/tomoyo/ with CONFIG_SECURITY_TOMOYO=y .
security/tomoyo/common.c:896:9: error: incompatible types in comparison
expression (different address spaces)
security/tomoyo/common.c:896:9: error: incompatible types in comparison
expression (different address spaces)
---------- security/tomoyo/common.c ----------
896: list_for_each_cookie(head->r.acl, &tomoyo_kernel_namespace.
897: policy_list[TOMOYO_ID_MANAGER]) {
---------- security/tomoyo/common.h ----------
1320: /**
1321: * list_for_each_cookie - iterate over a list with cookie.
1322: * @pos: the &struct list_head to use as a loop cursor.
1323: * @head: the head for your list.
1324: */
1325: #define list_for_each_cookie(pos, head) \
1326: if (!pos) \
1327: pos = srcu_dereference((head)->next, &tomoyo_ss); \
1328: for ( ; pos != (head); pos = srcu_dereference(pos->next,
&tomoyo_ss))
Both head->r.acl and
&tomoyo_kernel_namespace.policy_list[TOMOYO_ID_MANAGER]->next
refer normal kernel address space. Thus, I think that this warning is a false
positive.
This warning goes away if I disable rcu_dereference_sparse() call in
__rcu_dereference_check() from srcu_dereference_check() from srcu_dereference().
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -605,7 +605,7 @@ static inline void rcu_preempt_sleep_check(void)
/* Dependency order vs. p above. */ \
typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
- rcu_dereference_sparse(p, space); \
+ /*rcu_dereference_sparse(p, space); */ \
((typeof(*p) __force __kernel *)(________p1)); \
})
#define __rcu_dereference_protected(p, c, space) \
Regards.
