[PATCH] lockdep: fix sk->sk_callback_lock locking

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

=========================================================
[ INFO: possible irq lock inversion dependency detected ]
2.6.19-rc6 #4
---------------------------------------------------------
nc/1854 just changed the state of lock:
 (af_callback_keys + sk->sk_family#2){-.-?}, at: [<c0268a7f>] sock_def_error_report+0x1f/0x90
but this lock was taken by another, soft-irq-safe lock in the past:
 (slock-AF_INET){-+..}

and interrupts could create inverse lock ordering between them.

stack backtrace:
 [<c0103f36>] show_trace_log_lvl+0x26/0x40
 [<c010406b>] show_trace+0x1b/0x20
 [<c01049e4>] dump_stack+0x24/0x30
 [<c013738c>] print_irq_inversion_bug+0x10c/0x130
 [<c01374f2>] check_usage_backwards+0x42/0x50
 [<c0137912>] mark_lock+0x312/0x620
 [<c0138925>] __lock_acquire+0x4c5/0xcb0
 [<c0139499>] lock_acquire+0x69/0x90
 [<c02ddc49>] _read_lock+0x39/0x50
 [<c026778c>] sock_def_wakeup+0x1c/0x60
 [<c02b7d73>] inet_shutdown+0x93/0xf0
 [<c02648d2>] sys_shutdown+0x32/0x60
 [<c0266284>] sys_socketcall+0x1d4/0x260
 [<c01031f3>] syscall_call+0x7/0xb
 =======================

stack backtrace:
 [<c0103f36>] show_trace_log_lvl+0x26/0x40
 [<c010406b>] show_trace+0x1b/0x20
 [<c01049e4>] dump_stack+0x24/0x30
 [<c013738c>] print_irq_inversion_bug+0x10c/0x130
 [<c01374f2>] check_usage_backwards+0x42/0x50
 [<c0137912>] mark_lock+0x312/0x620
 [<c0138925>] __lock_acquire+0x4c5/0xcb0
 [<c0139499>] lock_acquire+0x69/0x90
 [<c02ddc59>] _read_lock+0x39/0x50
 [<c0268a7f>] sock_def_error_report+0x1f/0x90
 [<c029b968>] tcp_disconnect+0x318/0x490
 [<c02b9110>] inet_stream_connect+0x220/0x260
 [<c0264adb>] sys_connect+0x6b/0x90
 [<c026614f>] sys_socketcall+0x9f/0x260
 [<c01031f3>] syscall_call+0x7/0xb
 =======================

sk->sk_callback_lock is usually only read locked from softirq context
however it seems lockdep found two spots that are reachable from process
context, thus creating the possibility of a deadlock.

For now fix these two call sites with manual disabling of softirqs; if
more of these sites are found we might consider changing the read_lock() to
read_lock_bh().

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Martin Josefsson <gandalf@wlug.westbo.se>
---
 net/ipv4/af_inet.c |    2 ++
 net/ipv4/tcp.c     |    2 ++
 2 files changed, 4 insertions(+)

Index: linux-2.6-netdev/net/ipv4/af_inet.c
===================================================================
--- linux-2.6-netdev.orig/net/ipv4/af_inet.c	2006-11-27 14:41:51.000000000 +0100
+++ linux-2.6-netdev/net/ipv4/af_inet.c	2006-11-28 07:06:23.000000000 +0100
@@ -731,7 +731,9 @@ int inet_shutdown(struct socket *sock, i
 	}
 
 	/* Wake up anyone sleeping in poll. */
+	local_bh_disable();
 	sk->sk_state_change(sk);
+	local_bh_enable();
 	release_sock(sk);
 	return err;
 }
Index: linux-2.6-netdev/net/ipv4/tcp.c
===================================================================
--- linux-2.6-netdev.orig/net/ipv4/tcp.c	2006-11-28 07:06:16.000000000 +0100
+++ linux-2.6-netdev/net/ipv4/tcp.c	2006-11-28 07:06:20.000000000 +0100
@@ -1765,7 +1765,9 @@ int tcp_disconnect(struct sock *sk, int 
 
 	BUG_TRAP(!inet->num || icsk->icsk_bind_hash);
 
+	local_bh_disable();
 	sk->sk_error_report(sk);
+	local_bh_enable();
 	return err;
 }