Subject: net-flip-lock-dep-thingy.patch
From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 28 Jun 2011 10:59:58 +0200
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.6/older/patches-4.6.2-rt5.tar.xz

=======================================================
[ INFO: possible circular locking dependency detected ]
3.0.0-rc3+ #26
-------------------------------------------------------
ip/1104 is trying to acquire lock:
 (local_softirq_lock){+.+...}, at: [<ffffffff81056d12>] __local_lock+0x25/0x68

but task is already holding lock:
 (sk_lock-AF_INET){+.+...}, at: [<ffffffff81433308>] lock_sock+0x10/0x12

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (sk_lock-AF_INET){+.+...}:
       [<ffffffff810836e5>] lock_acquire+0x103/0x12e
       [<ffffffff813e2781>] lock_sock_nested+0x82/0x92
       [<ffffffff81433308>] lock_sock+0x10/0x12
       [<ffffffff81433afa>] tcp_close+0x1b/0x355
       [<ffffffff81453c99>] inet_release+0xc3/0xcd
       [<ffffffff813dff3f>] sock_release+0x1f/0x74
       [<ffffffff813dffbb>] sock_close+0x27/0x2b
       [<ffffffff81129c63>] fput+0x11d/0x1e3
       [<ffffffff81126577>] filp_close+0x70/0x7b
       [<ffffffff8112667a>] sys_close+0xf8/0x13d
       [<ffffffff814ae882>] system_call_fastpath+0x16/0x1b

-> #0 (local_softirq_lock){+.+...}:
       [<ffffffff81082ecc>] __lock_acquire+0xacc/0xdc8
       [<ffffffff810836e5>] lock_acquire+0x103/0x12e
       [<ffffffff814a7e40>] _raw_spin_lock+0x3b/0x4a
       [<ffffffff81056d12>] __local_lock+0x25/0x68
       [<ffffffff81056d8b>] local_bh_disable+0x36/0x3b
       [<ffffffff814a7fc4>] _raw_write_lock_bh+0x16/0x4f
       [<ffffffff81433c38>] tcp_close+0x159/0x355
       [<ffffffff81453c99>] inet_release+0xc3/0xcd
       [<ffffffff813dff3f>] sock_release+0x1f/0x74
       [<ffffffff813dffbb>] sock_close+0x27/0x2b
       [<ffffffff81129c63>] fput+0x11d/0x1e3
       [<ffffffff81126577>] filp_close+0x70/0x7b
       [<ffffffff8112667a>] sys_close+0xf8/0x13d
       [<ffffffff814ae882>] system_call_fastpath+0x16/0x1b

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(sk_lock-AF_INET);
                               lock(local_softirq_lock);
                               lock(sk_lock-AF_INET);
  lock(local_softirq_lock);

 *** DEADLOCK ***

1 lock held by ip/1104:
 #0:  (sk_lock-AF_INET){+.+...}, at: [<ffffffff81433308>] lock_sock+0x10/0x12

stack backtrace:
Pid: 1104, comm: ip Not tainted 3.0.0-rc3+ #26
Call Trace:
 [<ffffffff81081649>] print_circular_bug+0x1f8/0x209
 [<ffffffff81082ecc>] __lock_acquire+0xacc/0xdc8
 [<ffffffff81056d12>] ? __local_lock+0x25/0x68
 [<ffffffff810836e5>] lock_acquire+0x103/0x12e
 [<ffffffff81056d12>] ? __local_lock+0x25/0x68
 [<ffffffff81046c75>] ? get_parent_ip+0x11/0x41
 [<ffffffff814a7e40>] _raw_spin_lock+0x3b/0x4a
 [<ffffffff81056d12>] ? __local_lock+0x25/0x68
 [<ffffffff81046c8c>] ? get_parent_ip+0x28/0x41
 [<ffffffff81056d12>] __local_lock+0x25/0x68
 [<ffffffff81056d8b>] local_bh_disable+0x36/0x3b
 [<ffffffff81433308>] ? lock_sock+0x10/0x12
 [<ffffffff814a7fc4>] _raw_write_lock_bh+0x16/0x4f
 [<ffffffff81433c38>] tcp_close+0x159/0x355
 [<ffffffff81453c99>] inet_release+0xc3/0xcd
 [<ffffffff813dff3f>] sock_release+0x1f/0x74
 [<ffffffff813dffbb>] sock_close+0x27/0x2b
 [<ffffffff81129c63>] fput+0x11d/0x1e3
 [<ffffffff81126577>] filp_close+0x70/0x7b
 [<ffffffff8112667a>] sys_close+0xf8/0x13d
 [<ffffffff814ae882>] system_call_fastpath+0x16/0x1b


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 net/core/sock.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2421,12 +2421,11 @@ void lock_sock_nested(struct sock *sk, i
 	if (sk->sk_lock.owned)
 		__lock_sock(sk);
 	sk->sk_lock.owned = 1;
-	spin_unlock(&sk->sk_lock.slock);
+	spin_unlock_bh(&sk->sk_lock.slock);
 	/*
 	 * The sk_lock has mutex_lock() semantics here:
 	 */
 	mutex_acquire(&sk->sk_lock.dep_map, subclass, 0, _RET_IP_);
-	local_bh_enable();
 }
 EXPORT_SYMBOL(lock_sock_nested);
 
