From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: paulmck@linux.vnet.ibm.com
Cc: josh@joshtriplett.org, rostedt@goodmis.org,
mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
linux-kernel@vger.kernel.org
Subject: Re: [srcu] Can we suppress sparse warning?
Date: Sat, 12 Nov 2016 23:26:15 +0900 [thread overview]
Message-ID: <201611122326.GGI69239.OJLFtQVFMHOFSO@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20161109185810.GM4127@linux.vnet.ibm.com>
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.
next prev parent reply other threads:[~2016-11-12 14:26 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-09 11:36 [srcu] Can we suppress sparse warning? Tetsuo Handa
2016-11-09 18:58 ` Paul E. McKenney
2016-11-12 14:26 ` Tetsuo Handa [this message]
2016-11-12 19:17 ` Paul E. McKenney
2016-11-13 12:55 ` Tetsuo Handa
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