net/ipv6/addrconf: fix wdog_bark caused by infinite spinning on a deadlock

A synchronization issue may occur while addrconf_ifdown(),
when it updates inet6_addr_lst[] with already destroyed *ifp
by ipv6_add/del_addr(), using the same addrconf_hash_lock.

[core 0]                                        [core 1]
   |                                               |
   |->ipv6_add_addr                                |->addrconf_ifdown
       |                                               |
       |                                               |-> spin_lock(&addrconf_hash_lock);
       |                                               |-> remove ifa->addr_lst from inet6_addr_lst
       |                                               |-> spin_unlock(&addrconf_hash_lock);
       |-> spin_lock(&addrconf_hash_lock);             |
       |-> add ifa->addr_lst to inet6_addr_lst[hash]   |
       |-> spin_unlock(&addrconf_hash_lock);           |
       |-> write_lock(&idev-lock);                     |
       |-> add ifa->if_list to idev->addr_list         |
       |-> write_unlock(&idev->lock);                  |
       |                                               |-> write_lock(&idev->lock);
       |                                               |-> remove ifa->if_list from idev->addr_list
       |                                               |-> write_unlock(&idev->lock);

[28055.378524] ------------[ cut here ]------------
[28055.378591] WARNING: at net/ipv6/addrconf.c:546 inet6_ifa_finish_destroy+0x98/0xc8()
[28055.378691] [<c010de1c>] (unwind_backtrace+0x0/0x144) from [<c09fd08c>] (dump_stack+0x20/0x24)
[28055.378747] [<c09fd08c>] (dump_stack+0x20/0x24) from [<c0192adc>] (warn_slowpath_common+0x58/0x70)
[28055.378840] [<c0192adc>] (warn_slowpath_common+0x58/0x70) from [<c0192bec>] (warn_slowpath_null+0x2c/0x34)
[28055.378931] [<c0192bec>] (warn_slowpath_null+0x2c/0x34) from [<c0911a90>] (inet6_ifa_finish_destroy+0x98/0xc8)
[28055.379026] [<c0911a90>] (inet6_ifa_finish_destroy+0x98/0xc8) from [<c091498c>] (addrconf_ifdown+0x2e4/0x430)
[28055.379120] [<c091498c>] (addrconf_ifdown+0x2e4/0x430) from [<c0915b70>] (addrconf_notify+0xe4/0x3ac)
[28055.379209] [<c0915b70>] (addrconf_notify+0xe4/0x3ac) from [<c01b9df0>] (notifier_call_chain+0x54/0x94)
[28055.379321] [<c01b9df0>] (notifier_call_chain+0x54/0x94) from [<c01ba3ac>] (__raw_notifier_call_chain+0x24/0x2c)
[28055.379379] [<c01ba3ac>] (__raw_notifier_call_chain+0x24/0x2c) from [<c01ba3dc>] (raw_notifier_call_chain+0x28/0x30)
[28055.379475] [<c01ba3dc>] (raw_notifier_call_chain+0x28/0x30) from [<c0840ea4>] (call_netdevice_notifiers+0x38/0x60)
[28055.379568] [<c0840ea4>] (call_netdevice_notifiers+0x38/0x60) from [<c0844d5c>] (__dev_notify_flags+0x3c/0x6c)
[28055.379657] [<c0844d5c>] (__dev_notify_flags+0x3c/0x6c) from [<c0844dcc>] (dev_change_flags+0x40/0x58)
[28055.379747] [<c0844dcc>] (dev_change_flags+0x40/0x58) from [<c08d2834>] (devinet_ioctl+0x79c/0x8bc)
[28055.379837] [<c08d2834>] (devinet_ioctl+0x79c/0x8bc) from [<c08d3488>] (inet_ioctl+0x1c0/0x1d0)
[28055.379928] [<c08d3488>] (inet_ioctl+0x1c0/0x1d0) from [<c082d7f0>] (sock_ioctl+0x80/0x248)
[28055.379982] [<c082d7f0>] (sock_ioctl+0x80/0x248) from [<c0275364>] (do_vfs_ioctl+0x94/0x5bc)
[28055.380071] [<c0275364>] (do_vfs_ioctl+0x94/0x5bc) from [<c0275908>] (sys_ioctl+0x7c/0x8c)
[28055.380164] [<c0275908>] (sys_ioctl+0x7c/0x8c) from [<c0107300>] (ret_fast_syscall+0x0/0x30)
[28055.380252] ---[ end trace 920b8b321354f066 ]---
[28061.735021] Watchdog bark! Now = 28061.735014
[28061.735106] Watchdog last pet at 28050.179294
[28061.735245] cpu alive mask from last pet 0-3
[28061.735321] Causing a watchdog bite!

The addrconf_hash_lock should cover both modification of inet6_addr_list and idev->addr_list
to resolve any possible synchronization issue between addrconf_ifdown() and ipv6_add/del_addr().

Bug: 11293746
Change-Id: If263fc375b411bf21eacade0d094bff95939f7fe
Signed-off-by: David C. Park <davidc.park@lge.com>