[3.5.y.z,extended,stable] Patch "tipc: fix lockdep warning during bearer initialization" has been added to staging queue

This is a note to let you know that I have just added a patch titled

    tipc: fix lockdep warning during bearer initialization

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

From f3d4e5d27e69f3524de7c579f0bec38b1e5e4d9a Mon Sep 17 00:00:00 2001
From: Ying Xue <ying.xue@windriver.com>
Date: Thu, 16 Aug 2012 12:09:07 +0000
Subject: [PATCH] tipc: fix lockdep warning during bearer initialization

commit 4225a398c1352a7a5c14dc07277cb5cc4473983b upstream.

When the lockdep validator is enabled, it will report the below
warning when we enable a TIPC bearer:

[ INFO: possible irq lock inversion dependency detected ]
---------------------------------------------------------
Possible interrupt unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(ptype_lock);
                                local_irq_disable();
                                lock(tipc_net_lock);
                                lock(ptype_lock);
   <Interrupt>
   lock(tipc_net_lock);

  *** DEADLOCK ***

the shortest dependencies between 2nd lock and 1st lock:
  -> (ptype_lock){+.+...} ops: 10 {
[...]
SOFTIRQ-ON-W at:
                      [<c1089418>] __lock_acquire+0x528/0x13e0
                      [<c108a360>] lock_acquire+0x90/0x100
                      [<c1553c38>] _raw_spin_lock+0x38/0x50
                      [<c14651ca>] dev_add_pack+0x3a/0x60
                      [<c182da75>] arp_init+0x1a/0x48
                      [<c182dce5>] inet_init+0x181/0x27e
                      [<c1001114>] do_one_initcall+0x34/0x170
                      [<c17f7329>] kernel_init+0x110/0x1b2
                      [<c155b6a2>] kernel_thread_helper+0x6/0x10
[...]
   ... key      at: [<c17e4b10>] ptype_lock+0x10/0x20
   ... acquired at:
    [<c108a360>] lock_acquire+0x90/0x100
    [<c1553c38>] _raw_spin_lock+0x38/0x50
    [<c14651ca>] dev_add_pack+0x3a/0x60
    [<c8bc18d2>] enable_bearer+0xf2/0x140 [tipc]
    [<c8bb283a>] tipc_enable_bearer+0x1ba/0x450 [tipc]
    [<c8bb3a04>] tipc_cfg_do_cmd+0x5c4/0x830 [tipc]
    [<c8bbc032>] handle_cmd+0x42/0xd0 [tipc]
    [<c148e802>] genl_rcv_msg+0x232/0x280
    [<c148d3f6>] netlink_rcv_skb+0x86/0xb0
    [<c148e5bc>] genl_rcv+0x1c/0x30
    [<c148d144>] netlink_unicast+0x174/0x1f0
    [<c148ddab>] netlink_sendmsg+0x1eb/0x2d0
    [<c1456bc1>] sock_aio_write+0x161/0x170
    [<c1135a7c>] do_sync_write+0xac/0xf0
    [<c11360f6>] vfs_write+0x156/0x170
    [<c11361e2>] sys_write+0x42/0x70
    [<c155b0df>] sysenter_do_call+0x12/0x38
[...]
}
  -> (tipc_net_lock){+..-..} ops: 4 {
[...]
    IN-SOFTIRQ-R at:
                     [<c108953a>] __lock_acquire+0x64a/0x13e0
                     [<c108a360>] lock_acquire+0x90/0x100
                     [<c15541cd>] _raw_read_lock_bh+0x3d/0x50
                     [<c8bb874d>] tipc_recv_msg+0x1d/0x830 [tipc]
                     [<c8bc195f>] recv_msg+0x3f/0x50 [tipc]
                     [<c146a5fa>] __netif_receive_skb+0x22a/0x590
                     [<c146ab0b>] netif_receive_skb+0x2b/0xf0
                     [<c13c43d2>] pcnet32_poll+0x292/0x780
                     [<c146b00a>] net_rx_action+0xfa/0x1e0
                     [<c103a4be>] __do_softirq+0xae/0x1e0
[...]
}

>From the log, we can see three different call chains between
CPU0 and CPU1:

Time 0 on CPU0:

  kernel_init()->inet_init()->dev_add_pack()

At time 0, the ptype_lock is held by CPU0 in dev_add_pack();

Time 1 on CPU1:

  tipc_enable_bearer()->enable_bearer()->dev_add_pack()

At time 1, tipc_enable_bearer() first holds tipc_net_lock, and then
wants to take ptype_lock to register TIPC protocol handler into the
networking stack.  But the ptype_lock has been taken by dev_add_pack()
on CPU0, so at this time the dev_add_pack() running on CPU1 has to be
busy looping.

Time 2 on CPU0:

  netif_receive_skb()->recv_msg()->tipc_recv_msg()

At time 2, an incoming TIPC packet arrives at CPU0, hence
tipc_recv_msg() will be invoked. In tipc_recv_msg(), it first wants
to hold tipc_net_lock.  At the moment, below scenario happens:

On CPU0, below is our sequence of taking locks:

  lock(ptype_lock)->lock(tipc_net_lock)

On CPU1, our sequence of taking locks looks like:

  lock(tipc_net_lock)->lock(ptype_lock)

Obviously deadlock may happen in this case.

But please note the deadlock possibly doesn't occur at all when the
first TIPC bearer is enabled.  Before enable_bearer() -- running on
CPU1 does not hold ptype_lock, so the TIPC receive handler (i.e.
recv_msg()) is not registered successfully via dev_add_pack(), so
the tipc_recv_msg() cannot be called by recv_msg() even if a TIPC
message comes to CPU0. But when the second TIPC bearer is
registered, the deadlock can perhaps really happen.

To fix it, we will push the work of registering TIPC protocol
handler into workqueue context. After the change, both paths taking
ptype_lock are always in process contexts, thus, the deadlock should
never occur.

Signed-off-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 net/tipc/eth_media.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

--
1.8.3.2