[Patch net] bridge: resolve a false alarm of lockdep

[Patch net] bridge: resolve a false alarm of lockdep

[Cong Wang]

Andrei reported a false alarm of lockdep at net/bridge/br_fdb.c:109,
this is because in Andrei's case, a spin_bug() was already triggered
before this, therefore the debug_locks is turned off, lockdep_is_held()
is no longer accurate after that. We should use lockdep_assert_held_once()
instead of lockdep_is_held() to respect debug_locks.

Reported-by: Andrei Vagin <avagin@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
 net/bridge/br_fdb.c     | 2 +-
 net/bridge/br_private.h | 9 ---------
 2 files changed, 1 insertion(+), 10 deletions(-)

diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
index 4f598dc..6e08b71 100644
--- a/net/bridge/br_fdb.c
+++ b/net/bridge/br_fdb.c
@@ -106,7 +106,7 @@ static struct net_bridge_fdb_entry *br_fdb_find(struct net_bridge *br,
 	struct hlist_head *head = &br->hash[br_mac_hash(addr, vid)];
 	struct net_bridge_fdb_entry *fdb;
 
-	WARN_ON_ONCE(!br_hash_lock_held(br));
+	lockdep_assert_held_once(&br->hash_lock);
 
 	rcu_read_lock();
 	fdb = fdb_find_rcu(head, addr, vid);
diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index 2288fca..6136818 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -531,15 +531,6 @@ int br_fdb_external_learn_add(struct net_bridge *br, struct net_bridge_port *p,
 int br_fdb_external_learn_del(struct net_bridge *br, struct net_bridge_port *p,
 			      const unsigned char *addr, u16 vid);
 
-static inline bool br_hash_lock_held(struct net_bridge *br)
-{
-#ifdef CONFIG_LOCKDEP
-	return lockdep_is_held(&br->hash_lock);
-#else
-	return true;
-#endif
-}
-
 /* br_forward.c */
 enum br_pkt_type {
 	BR_PKT_UNICAST,
-- 
2.5.5

Re: [Patch net] bridge: resolve a false alarm of lockdep

[Nikolay Aleksandrov]

On 16/03/17 19:32, Cong Wang wrote:
> Andrei reported a false alarm of lockdep at net/bridge/br_fdb.c:109,
> this is because in Andrei's case, a spin_bug() was already triggered
> before this, therefore the debug_locks is turned off, lockdep_is_held()
> is no longer accurate after that. We should use lockdep_assert_held_once()
> instead of lockdep_is_held() to respect debug_locks.
> 
> Reported-by: Andrei Vagin <avagin@gmail.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
> ---
>  net/bridge/br_fdb.c     | 2 +-
>  net/bridge/br_private.h | 9 ---------
>  2 files changed, 1 insertion(+), 10 deletions(-)
> 

Interesting, thanks Cong!

Fixes: 410b3d48f5111 ("bridge: fdb: add proper lock checks in searching functions")

Acked-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>

Re: [Patch net] bridge: resolve a false alarm of lockdep

[David Miller]

From: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Date: Thu, 16 Mar 2017 19:36:07 +0200

> On 16/03/17 19:32, Cong Wang wrote:
>> Andrei reported a false alarm of lockdep at net/bridge/br_fdb.c:109,
>> this is because in Andrei's case, a spin_bug() was already triggered
>> before this, therefore the debug_locks is turned off, lockdep_is_held()
>> is no longer accurate after that. We should use lockdep_assert_held_once()
>> instead of lockdep_is_held() to respect debug_locks.
>> 
>> Reported-by: Andrei Vagin <avagin@gmail.com>
>> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
>> ---
>>  net/bridge/br_fdb.c     | 2 +-
>>  net/bridge/br_private.h | 9 ---------
>>  2 files changed, 1 insertion(+), 10 deletions(-)
>> 
> 
> Interesting, thanks Cong!
> 
> Fixes: 410b3d48f5111 ("bridge: fdb: add proper lock checks in searching functions")
> 
> Acked-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>

Applied, thanks.