linux-kernel - [PATCH RFC] hlist_add_tail

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Date:   Wed, 23 Nov 2016 22:48:19 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     David Miller <davem@...emloft.net>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Arnd Bergmann <arnd@...db.de>
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH RFC] hlist_add_tail_rcu disable sparse warning

sparse is unhappy about this code in hlist_add_tail_rcu:

        struct hlist_node *i, *last = NULL;

        for (i = hlist_first_rcu(h); i; i = hlist_next_rcu(i))
                last = i;

This is because hlist_next_rcu and hlist_next_rcu return
__rcu pointers.

The following trivial patch disables the warning
without changing the behaviour in any way.

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>

---

I would appreciate review to confirm the function doesn't
do anything unsafe though.

In particular, should this use __hlist_for_each_rcu instead?
I note that __hlist_for_each_rcu does rcu_dereference
internally, which is missing here.

compile-tested only.

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 8beb98d..33574db 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -511,7 +511,7 @@ static inline void hlist_add_tail_rcu(struct hlist_node *n,
 {
 	struct hlist_node *i, *last = NULL;

-	for (i = hlist_first_rcu(h); i; i = hlist_next_rcu(i))
+	for (i = h->first; i; i = i->next)
 		last = i;

 	if (last) {