On Sat, Nov 12, 2016 at 11:26:15PM +0900, Tetsuo Handa wrote: > 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))
This definition will be fun if used in an "if" statement, but I will leave that in your capable hands. > > 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) \ OK. One approach would be for you to replace your: pos = srcu_dereference((head)->next, &tomoyo_ss); with: pos = ecu_dereference_raw((head)->next); This will suppress the sparse complaint, but would also suppress the lockdep complaint about using list_for_each_cookie() unprotected by an SRCU read-side critical section. But this can be handled by placing an appropriate RCU_LOCKDEP_WARN() in list_for_each_cookie(). Does that work for you? Thanx, Paul