Messages in this thread | | | Date | Thu, 1 Apr 2010 18:36:42 +0200 | From | Oleg Nesterov <> | Subject | Re: [Patch] workqueue: move lockdep annotations up to destroy_workqueue() |
| |
On 04/01, Cong Wang wrote: > >> I must have missed something, but it seems to me this patch tries to >> supress the valid warning. >> >> Could you please clarify? > > Sure, below is the whole warning. Please teach me how this is valid.
Oh, I can never understand the output from lockdep, it is much more clever than me ;)
But at first glance,
> Mar 31 16:15:02 dhcp-66-70-5 kernel: -> #2 (rtnl_mutex){+.+.+.}: > Mar 31 16:15:02 dhcp-66-70-5 kernel: [<ffffffff810a6bc1>] validate_chain+0x1019/0x1540 > Mar 31 16:15:02 dhcp-66-70-5 kernel: [<ffffffff810a7e75>] __lock_acquire+0xd8d/0xe55 > Mar 31 16:15:02 dhcp-66-70-5 kernel: [<ffffffff810aa3a4>] lock_acquire+0x160/0x1af > Mar 31 16:15:02 dhcp-66-70-5 kernel: [<ffffffff815523f8>] mutex_lock_nested+0x64/0x4e9 > Mar 31 16:15:02 dhcp-66-70-5 kernel: [<ffffffff8147af16>] rtnl_lock+0x1e/0x27 > Mar 31 16:15:02 dhcp-66-70-5 kernel: [<ffffffffa0836779>] bond_mii_monitor+0x39f/0x74b [bonding] > Mar 31 16:15:02 dhcp-66-70-5 kernel: [<ffffffff8108654f>] worker_thread+0x2da/0x46c > Mar 31 16:15:02 dhcp-66-70-5 kernel: [<ffffffff8108b1ea>] kthread+0xdd/0xec > Mar 31 16:15:02 dhcp-66-70-5 kernel: [<ffffffff81004894>] kernel_thread_helper+0x4/0x10
OK, so work->func() takes rtnl_mutex.
This means it is not safe to do flush_workqueue() or destroy_workqueue() under rtnl_lock(). This is known fact.
> Mar 31 16:15:03 dhcp-66-70-5 kernel: -> #0 ((bond_dev->name)){+.+...}: > Mar 31 16:15:03 dhcp-66-70-5 kernel: [<ffffffff810a6696>] validate_chain+0xaee/0x1540 > Mar 31 16:15:03 dhcp-66-70-5 kernel: [<ffffffff810a7e75>] __lock_acquire+0xd8d/0xe55 > Mar 31 16:15:03 dhcp-66-70-5 kernel: [<ffffffff810aa3a4>] lock_acquire+0x160/0x1af > Mar 31 16:15:03 dhcp-66-70-5 kernel: [<ffffffff81085278>] cleanup_workqueue_thread+0x59/0x10b > Mar 31 16:15:03 dhcp-66-70-5 kernel: [<ffffffff81085428>] destroy_workqueue+0x9c/0x107 > Mar 31 16:15:03 dhcp-66-70-5 kernel: [<ffffffffa0839d32>] bond_uninit+0x524/0x58a [bonding] > Mar 31 16:15:03 dhcp-66-70-5 kernel: [<ffffffff8146967b>] rollback_registered_many+0x205/0x2e3 > Mar 31 16:15:03 dhcp-66-70-5 kernel: [<ffffffff81469783>] unregister_netdevice_many+0x2a/0x75 > Mar 31 16:15:03 dhcp-66-70-5 kernel: [<ffffffff8147ada3>] __rtnl_kill_links+0x8b/0x9d > Mar 31 16:15:03 dhcp-66-70-5 kernel: [<ffffffff8147adea>] __rtnl_link_unregister+0x35/0x72 > Mar 31 16:15:03 dhcp-66-70-5 kernel: [<ffffffff8147b293>] rtnl_link_unregister+0x2c/0x43
However, rtnl_link_unregister() takes rtnl_mutex and then bond_uninit() does cleanup_workqueue_thread().
So, looks like this warning is valid, this path can deadlock if destroy_workqueue() is called when bond->mii_work is queued.
Lockdep decided to blaim cpu_add_remove_lock in this chain.
Oleg.
| |