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net: fix a lockdep splat

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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 <[email protected]>
Tested-by: Tetsuo Handa <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
CC: Jarek Poplawski <[email protected]>
Tested-by: Eric Dumazet <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Eric Dumazet 2010-09-22 12:43:39 +00:00 • committed by David S. Miller
commit f064af1e50
6 changed files with 26 additions and 26 deletions
Download patch file Download diff file Expand all files Collapse all files

4
net/rds/tcp_connect.c
View file

@ -43,7 +43,7 @@ void rds_tcp_state_change(struct sock *sk)
struct rds_connection *conn;
struct rds_tcp_connection *tc;
read_lock(&sk->sk_callback_lock);
read_lock_bh(&sk->sk_callback_lock);
conn = sk->sk_user_data;
if (conn == NULL) {
state_change = sk->sk_state_change;
@ -68,7 +68,7 @@ void rds_tcp_state_change(struct sock *sk)
break;
}
out:
read_unlock(&sk->sk_callback_lock);
read_unlock_bh(&sk->sk_callback_lock);
state_change(sk);
}

4
net/rds/tcp_listen.c
View file

@ -114,7 +114,7 @@ void rds_tcp_listen_data_ready(struct sock *sk, int bytes)
rdsdebug("listen data ready sk %p\n", sk);
read_lock(&sk->sk_callback_lock);
read_lock_bh(&sk->sk_callback_lock);
ready = sk->sk_user_data;
if (ready == NULL) { /* check for teardown race */
ready = sk->sk_data_ready;
@ -131,7 +131,7 @@ void rds_tcp_listen_data_ready(struct sock *sk, int bytes)
queue_work(rds_wq, &rds_tcp_listen_work);
out:
read_unlock(&sk->sk_callback_lock);
read_unlock_bh(&sk->sk_callback_lock);
ready(sk, bytes);
}

4
net/rds/tcp_recv.c
View file

@ -324,7 +324,7 @@ void rds_tcp_data_ready(struct sock *sk, int bytes)
rdsdebug("data ready sk %p bytes %d\n", sk, bytes);
read_lock(&sk->sk_callback_lock);
read_lock_bh(&sk->sk_callback_lock);
conn = sk->sk_user_data;
if (conn == NULL) { /* check for teardown race */
ready = sk->sk_data_ready;
@ -338,7 +338,7 @@ void rds_tcp_data_ready(struct sock *sk, int bytes)
if (rds_tcp_read_sock(conn, GFP_ATOMIC, KM_SOFTIRQ0) == -ENOMEM)
queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
out:
read_unlock(&sk->sk_callback_lock);
read_unlock_bh(&sk->sk_callback_lock);
ready(sk, bytes);
}

4
net/rds/tcp_send.c
View file

@ -224,7 +224,7 @@ void rds_tcp_write_space(struct sock *sk)
struct rds_connection *conn;
struct rds_tcp_connection *tc;
read_lock(&sk->sk_callback_lock);
read_lock_bh(&sk->sk_callback_lock);
conn = sk->sk_user_data;
if (conn == NULL) {
write_space = sk->sk_write_space;
@ -244,7 +244,7 @@ void rds_tcp_write_space(struct sock *sk)
queue_delayed_work(rds_wq, &conn->c_send_w, 0);
out:
read_unlock(&sk->sk_callback_lock);
read_unlock_bh(&sk->sk_callback_lock);
/*
* write_space is only called when data leaves tcp's send queue if