netdev - [PATCH] net: sched: Fix warnings from xchg() on RCU'd cookie pointer.

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Message-Id: <20180708.170358.1177815849312901978.davem@davemloft.net>
Date:   Sun, 08 Jul 2018 17:03:58 +0900 (KST)
From:   David Miller <davem@...emloft.net>
To:     netdev@...r.kernel.org
CC:     vladbu@...lanox.com, jiri@...lanox.com
Subject: [PATCH] net: sched: Fix warnings from xchg() on RCU'd cookie
 pointer.


The kbuild test robot reports:

>> net/sched/act_api.c:71:15: sparse: incorrect type in initializer (different address spaces) @@    expected struct tc_cookie [noderef] <asn:4>*__ret @@    got [noderef] <asn:4>*__ret @@
   net/sched/act_api.c:71:15:    expected struct tc_cookie [noderef] <asn:4>*__ret
   net/sched/act_api.c:71:15:    got struct tc_cookie *new_cookie
>> net/sched/act_api.c:71:13: sparse: incorrect type in assignment (different address spaces) @@    expected struct tc_cookie *old @@    got struct tc_cookie [noderef] <struct tc_cookie *old @@
   net/sched/act_api.c:71:13:    expected struct tc_cookie *old
   net/sched/act_api.c:71:13:    got struct tc_cookie [noderef] <asn:4>*[assigned] __ret
>> net/sched/act_api.c:132:48: sparse: dereference of noderef expression

Handle this in the usual way by force casting away the __rcu annotation
when we are using xchg() on it.

Fixes: eec94fdb0480 ("net: sched: use rcu for action cookie update")
Reported-by: kbuild test robot <lkp@...el.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
---
 net/sched/act_api.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index bf1c35f3deb6..66dc19746c63 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -68,7 +68,7 @@ static void tcf_set_action_cookie(struct tc_cookie __rcu **old_cookie,
 {
 	struct tc_cookie *old;
 
-	old = xchg(old_cookie, new_cookie);
+	old = xchg((__force struct tc_cookie **)old_cookie, new_cookie);
 	if (old)
 		call_rcu(&old->rcu, tcf_free_cookie_rcu);
 }
-- 
2.17.1