[PATCH net-next RESEND 1/2] tipc: fix RCU sparse error

From: Ying Xue
Date: Wed Dec 10 2014 - 03:46:37 EST

The commit 97ede29e80ee ("tipc: convert name table read-write lock to
RCU") involves the following sparse when using

make ARCH=x86_64 allmodconfig
make C=1 CF=-D__CHECK_ENDIAN__

net/tipc/name_table.c:1136:17: sparse: incompatible types in comparison expression (different address spaces)
net/tipc/name_table.c:1136:17: sparse: incompatible types in comparison expression (different address spaces)

To silence above spare complaint, an RCU annotation should be added
to "next" pointer of hlist_node structure through hlist_next_rcu()
macro when iterating over a hlist with hlist_for_each_entry_from_rcu().

By the way, this commit also simplifies the way of dereferencing
the first element of a hlist_head list by replacing
hlist_for_each_entry_rcu() with hlist_entry_safe().

Reported-by: Kbuild test robot <kbuild-all@xxxxxx>
Cc: Kbuild test robot <kbuild-all@xxxxxx>
Signed-off-by: Ying Xue <ying.xue@xxxxxxxxxxxxx>
include/linux/rculist.h | 4 ++--
net/tipc/name_table.c | 6 +++---
2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index aa79b3c..866d9c9 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -549,8 +549,8 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
#define hlist_for_each_entry_from_rcu(pos, member) \
for (; pos; \
- pos = hlist_entry_safe(rcu_dereference((pos)->member.next),\
- typeof(*(pos)), member))
+ pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu( \
+ &(pos)->member)), typeof(*(pos)), member))

#endif /* __KERNEL__ */
diff --git a/net/tipc/name_table.c b/net/tipc/name_table.c
index c8df022..fa4341f 100644
--- a/net/tipc/name_table.c
+++ b/net/tipc/name_table.c
@@ -1110,7 +1110,7 @@ static int __tipc_nl_seq_list(struct tipc_nl_msg *msg, u32 *last_type,
u32 *last_lower, u32 *last_publ)
struct hlist_head *seq_head;
- struct name_seq *seq = NULL;
+ struct name_seq *seq;
int err;
int i;

@@ -1127,8 +1127,8 @@ static int __tipc_nl_seq_list(struct tipc_nl_msg *msg, u32 *last_type,
if (!seq)
return -EPIPE;
} else {
- hlist_for_each_entry_rcu(seq, seq_head, ns_list)
- break;
+ seq = hlist_entry_safe(rcu_dereference_raw(
+ hlist_first_rcu(seq_head)), struct name_seq, ns_list);
if (!seq)

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