Subject: net-next rcu_dereference_check() warning

From: Dimitris Michailidis <[email-masked]>
Date: Mon, 27 Sep 2010 09:30:09 -0700

With today's net-next I am getting the below.  It appears to be recent, it 
wasn't happening with the net-next I was using last week.

===================================================
[ INFO: suspicious rcu_dereference_check() usage. ]
---------------------------------------------------
/build/net-next-2.6/include/linux/netpoll.h:67 invoked 
rcu_dereference_check() without protection!

other info that might help us debug this:

rcu_scheduler_active = 1, debug_locks = 0
1 lock held by ypbind/5046:
  #0:  (sk_lock-AF_INET){+.+.+.}, at: [<ffffffff81503139>] 
udp_sendmsg+0x3fd/0x5dc

stack backtrace:
Pid: 5046, comm: ypbind Not tainted 2.6.36-rc3+ #16
Call Trace:
  [<ffffffff810668e4>] lockdep_rcu_dereference+0xaa/0xb3
  [<ffffffff814b8d09>] netif_rx+0x53/0x1cf
  [<ffffffff810313b7>] ? get_parent_ip+0x11/0x41
  [<ffffffff814b9068>] netif_rx_ni+0x23/0x5d
  [<ffffffff814e57a9>] ip_dev_loopback_xmit+0xc5/0xcb
  [<ffffffff814e593c>] ip_mc_output+0x18d/0x1a5
  [<ffffffff814e30ec>] ip_local_out+0x62/0x66
  [<ffffffff814e33cb>] ip_push_pending_frames+0x2db/0x337
  [<ffffffff81501b55>] udp_push_pending_frames+0x2de/0x34c
  [<ffffffff81503139>] ? udp_sendmsg+0x3fd/0x5dc
  [<ffffffff8150322a>] udp_sendmsg+0x4ee/0x5dc
  [<ffffffff8150aa74>] inet_sendmsg+0x13a/0x145
  [<ffffffff8150a93a>] ? inet_sendmsg+0x0/0x145
  [<ffffffff814a6d24>] sock_sendmsg+0xc0/0xd9
  [<ffffffff8106aad4>] ? lock_release_non_nested+0xe5/0x296
  [<ffffffff810c8fb0>] ? might_fault+0x68/0xb8
  [<ffffffff810c8fb0>] ? might_fault+0x68/0xb8
  [<ffffffff810c8ff9>] ? might_fault+0xb1/0xb8
  [<ffffffff810c8fb0>] ? might_fault+0x68/0xb8
  [<ffffffff814a6672>] ? move_addr_to_kernel+0x3f/0x56
  [<ffffffff814a7458>] sys_sendto+0xe0/0x108
  [<ffffffff810f9a76>] ? d_kill+0x6c/0x74
  [<ffffffff810e99df>] ? fput+0x1ce/0x1dd
  [<ffffffff81002c9b>] system_call_fastpath+0x16/0x1b