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dingtianhong reported the following deadlock detected by lockdep: ====================================================== [ INFO: possible circular locking dependency detected ] 3.4.24.05-0.1-default #1 Not tainted ------------------------------------------------------- ksoftirqd/0/3 is trying to acquire lock: (&ndev->lock){+.+...}, at: [<ffffffff8147f804>] ipv6_get_lladdr+0x74/0x120 but task is already holding lock: (&mc->mca_lock){+.+...}, at: [<ffffffff8149d130>] mld_send_report+0x40/0x150 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&mc->mca_lock){+.+...}: [<ffffffff810a8027>] validate_chain+0x637/0x730 [<ffffffff810a8417>] __lock_acquire+0x2f7/0x500 [<ffffffff810a8734>] lock_acquire+0x114/0x150 [<ffffffff814f691a>] rt_spin_lock+0x4a/0x60 [<ffffffff8149e4bb>] igmp6_group_added+0x3b/0x120 [<ffffffff8149e5d8>] ipv6_mc_up+0x38/0x60 [<ffffffff81480a4d>] ipv6_find_idev+0x3d/0x80 [<ffffffff81483175>] addrconf_notify+0x3d5/0x4b0 [<ffffffff814fae3f>] notifier_call_chain+0x3f/0x80 [<ffffffff81073471>] raw_notifier_call_chain+0x11/0x20 [<ffffffff813d8722>] call_netdevice_notifiers+0x32/0x60 [<ffffffff813d92d4>] __dev_notify_flags+0x34/0x80 [<ffffffff813d9360>] dev_change_flags+0x40/0x70 [<ffffffff813ea627>] do_setlink+0x237/0x8a0 [<ffffffff813ebb6c>] rtnl_newlink+0x3ec/0x600 [<ffffffff813eb4d0>] rtnetlink_rcv_msg+0x160/0x310 [<ffffffff814040b9>] netlink_rcv_skb+0x89/0xb0 [<ffffffff813eb357>] rtnetlink_rcv+0x27/0x40 [<ffffffff81403e20>] netlink_unicast+0x140/0x180 [<ffffffff81404a9e>] netlink_sendmsg+0x33e/0x380 [<ffffffff813c4252>] sock_sendmsg+0x112/0x130 [<ffffffff813c537e>] __sys_sendmsg+0x44e/0x460 [<ffffffff813c5544>] sys_sendmsg+0x44/0x70 [<ffffffff814feab9>] system_call_fastpath+0x16/0x1b -> #0 (&ndev->lock){+.+...}: [<ffffffff810a798e>] check_prev_add+0x3de/0x440 [<ffffffff810a8027>] validate_chain+0x637/0x730 [<ffffffff810a8417>] __lock_acquire+0x2f7/0x500 [<ffffffff810a8734>] lock_acquire+0x114/0x150 [<ffffffff814f6c82>] rt_read_lock+0x42/0x60 [<ffffffff8147f804>] ipv6_get_lladdr+0x74/0x120 [<ffffffff8149b036>] mld_newpack+0xb6/0x160 [<ffffffff8149b18b>] add_grhead+0xab/0xc0 [<ffffffff8149d03b>] add_grec+0x3ab/0x460 [<ffffffff8149d14a>] mld_send_report+0x5a/0x150 [<ffffffff8149f99e>] igmp6_timer_handler+0x4e/0xb0 [<ffffffff8105705a>] call_timer_fn+0xca/0x1d0 [<ffffffff81057b9f>] run_timer_softirq+0x1df/0x2e0 [<ffffffff8104e8c7>] handle_pending_softirqs+0xf7/0x1f0 [<ffffffff8104ea3b>] __do_softirq_common+0x7b/0xf0 [<ffffffff8104f07f>] __thread_do_softirq+0x1af/0x210 [<ffffffff8104f1c1>] run_ksoftirqd+0xe1/0x1f0 [<ffffffff8106c7de>] kthread+0xae/0xc0 [<ffffffff814fff74>] kernel_thread_helper+0x4/0x10 actually we can just hold idev->lock before taking pmc->mca_lock, and avoid taking idev->lock again when iterating idev->addr_list, since the upper callers of mld_newpack() already take read_lock_bh(&idev->lock). Reported-by: dingtianhong <dingtianhong@huawei.com> Cc: dingtianhong <dingtianhong@huawei.com> Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org> Cc: David S. Miller <davem@davemloft.net> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org> Tested-by: Ding Tianhong <dingtianhong@huawei.com> Tested-by: Chen Weilong <chenweilong@huawei.com> Signed-off-by: Cong Wang <amwang@redhat.com> Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org> Signed-off-by: David S. Miller <davem@davemloft.net>