net: fix a lockdep splat

We have for each socket :

One spinlock (sk_slock.slock)
One rwlock (sk_callback_lock)

Possible scenarios are :

(A) (this is used in net/sunrpc/xprtsock.c)
read_lock(&sk->sk_callback_lock) (without blocking BH)
<BH>
spin_lock(&sk->sk_slock.slock);
...
read_lock(&sk->sk_callback_lock);
...

(B)
write_lock_bh(&sk->sk_callback_lock)
stuff
write_unlock_bh(&sk->sk_callback_lock)

(C)
spin_lock_bh(&sk->sk_slock)
...
write_lock_bh(&sk->sk_callback_lock)
stuff
write_unlock_bh(&sk->sk_callback_lock)
spin_unlock_bh(&sk->sk_slock)

This (C) case conflicts with (A) :

CPU1 [A]                         CPU2 [C]
read_lock(callback_lock)
<BH>                             spin_lock_bh(slock)
<wait to spin_lock(slock)>
                                 <wait to write_lock_bh(callback_lock)>

We have one problematic (C) use case in inet_csk_listen_stop() :

local_bh_disable();
bh_lock_sock(child); // spin_lock_bh(&sk->sk_slock)
WARN_ON(sock_owned_by_user(child));
...
sock_orphan(child); // write_lock_bh(&sk->sk_callback_lock)

lockdep is not happy with this, as reported by Tetsuo Handa

It seems only way to deal with this is to use read_lock_bh(callbacklock)
everywhere.

Thanks to Jarek for pointing a bug in my first attempt and suggesting
this solution.

Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Jarek Poplawski <jarkao2@gmail.com>
Tested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 4 deletions

diff --git a/net/core/sock.c b/net/core/sock.c
index b05b9b6ddb87..ef30e9d286e7 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1351,9 +1351,9 @@ int sock_i_uid(struct sock *sk)
 {
         int uid;
 
-        read_lock(&sk->sk_callback_lock);
+        read_lock_bh(&sk->sk_callback_lock);
         uid = sk->sk_socket ? SOCK_INODE(sk->sk_socket)->i_uid : 0;
-        read_unlock(&sk->sk_callback_lock);
+        read_unlock_bh(&sk->sk_callback_lock);
         return uid;
 }
 EXPORT_SYMBOL(sock_i_uid);
@@ -1362,9 +1362,9 @@ unsigned long sock_i_ino(struct sock *sk)
 {
         unsigned long ino;
 
-        read_lock(&sk->sk_callback_lock);
+        read_lock_bh(&sk->sk_callback_lock);
         ino = sk->sk_socket ? SOCK_INODE(sk->sk_socket)->i_ino : 0;
-        read_unlock(&sk->sk_callback_lock);
+        read_unlock_bh(&sk->sk_callback_lock);
         return ino;
 }
 EXPORT_SYMBOL(sock_i_ino);