Re: [BUG] e1000: possible deadlock scenario caught by lockdep

CC'd netdev, and e1000-devel

On Thu, 17 Nov 2011 17:27:00 -0800
Steven Rostedt [off-list ref] wrote:

I hit the following lockdep splat:

======================================================
[ INFO: possible circular locking dependency detected ]
3.2.0-rc2-test+ #14
-------------------------------------------------------
reboot/2316 is trying to acquire lock:
 ((&(&adapter->watchdog_task)->work)){+.+...}, at: [<ffffffff81069553>] wait_on_work+0x0/0xac

but task is already holding lock:
 (&adapter->mutex){+.+...}, at: [<ffffffff81359b1d>] __e1000_shutdown+0x56/0x1f5

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&adapter->mutex){+.+...}:
       [<ffffffff8108261a>] lock_acquire+0x103/0x158
       [<ffffffff8150bcf3>] __mutex_lock_common+0x6a/0x441
       [<ffffffff8150c13d>] mutex_lock_nested+0x1b/0x1d
       [<ffffffff81359288>] e1000_watchdog+0x56/0x4a4
       [<ffffffff8106a1b0>] process_one_work+0x1ef/0x3e0
       [<ffffffff8106b4e0>] worker_thread+0xda/0x15e
       [<ffffffff8106f00e>] kthread+0x9f/0xa7
       [<ffffffff81514e84>] kernel_thread_helper+0x4/0x10

-> #0 ((&(&adapter->watchdog_task)->work)){+.+...}:
       [<ffffffff81081e4a>] __lock_acquire+0xa29/0xd06
       [<ffffffff8108261a>] lock_acquire+0x103/0x158
       [<ffffffff81069590>] wait_on_work+0x3d/0xac
       [<ffffffff8106a616>] __cancel_work_timer+0xb9/0xff
       [<ffffffff8106a66e>] cancel_delayed_work_sync+0x12/0x14
       [<ffffffff81355c8f>] e1000_down_and_stop+0x2e/0x4a
       [<ffffffff813581ed>] e1000_down+0x116/0x176
       [<ffffffff81359b4a>] __e1000_shutdown+0x83/0x1f5
       [<ffffffff81359cd6>] e1000_shutdown+0x1a/0x43
       [<ffffffff8126fdad>] pci_device_shutdown+0x29/0x3d
       [<ffffffff8130c601>] device_shutdown+0xbe/0xf9
       [<ffffffff81065b17>] kernel_restart_prepare+0x31/0x38
       [<ffffffff81065b32>] kernel_restart+0x14/0x51
       [<ffffffff81065cd8>] sys_reboot+0x157/0x1b0
       [<ffffffff81513882>] system_call_fastpath+0x16/0x1b

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&adapter->mutex);
                               lock((&(&adapter->watchdog_task)->work));
                               lock(&adapter->mutex);
  lock((&(&adapter->watchdog_task)->work));

 *** DEADLOCK ***

2 locks held by reboot/2316:
 #0:  (reboot_mutex){+.+.+.}, at: [<ffffffff81065c20>] sys_reboot+0x9f/0x1b0
 #1:  (&adapter->mutex){+.+...}, at: [<ffffffff81359b1d>] __e1000_shutdown+0x56/0x1f5

stack backtrace:
Pid: 2316, comm: reboot Not tainted 3.2.0-rc2-test+ #14
Call Trace:
 [<ffffffff81503eb2>] print_circular_bug+0x1f8/0x209
 [<ffffffff81081e4a>] __lock_acquire+0xa29/0xd06
 [<ffffffff81069553>] ? wait_on_cpu_work+0x94/0x94
 [<ffffffff8108261a>] lock_acquire+0x103/0x158
 [<ffffffff81069553>] ? wait_on_cpu_work+0x94/0x94
 [<ffffffff810c7caf>] ? trace_preempt_on+0x2a/0x2f
 [<ffffffff81069590>] wait_on_work+0x3d/0xac
 [<ffffffff81069553>] ? wait_on_cpu_work+0x94/0x94
 [<ffffffff8106a616>] __cancel_work_timer+0xb9/0xff
 [<ffffffff8106a66e>] cancel_delayed_work_sync+0x12/0x14
 [<ffffffff81355c8f>] e1000_down_and_stop+0x2e/0x4a
 [<ffffffff813581ed>] e1000_down+0x116/0x176
 [<ffffffff81359b4a>] __e1000_shutdown+0x83/0x1f5
 [<ffffffff8150d51c>] ? _raw_spin_unlock+0x33/0x56
 [<ffffffff8130c583>] ? device_shutdown+0x40/0xf9
 [<ffffffff81359cd6>] e1000_shutdown+0x1a/0x43
 [<ffffffff81510757>] ? sub_preempt_count+0xa1/0xb4
 [<ffffffff8126fdad>] pci_device_shutdown+0x29/0x3d
 [<ffffffff8130c601>] device_shutdown+0xbe/0xf9
 [<ffffffff81065b17>] kernel_restart_prepare+0x31/0x38
 [<ffffffff81065b32>] kernel_restart+0x14/0x51
 [<ffffffff81065cd8>] sys_reboot+0x157/0x1b0
 [<ffffffff81072ccb>] ? hrtimer_cancel+0x17/0x24
 [<ffffffff8150c304>] ? do_nanosleep+0x74/0xac
 [<ffffffff8125c72d>] ? trace_hardirqs_off_thunk+0x3a/0x3c
 [<ffffffff8150e066>] ? error_sti+0x5/0x6
 [<ffffffff810c7c80>] ? time_hardirqs_off+0x2a/0x2f
 [<ffffffff8125c6ee>] ? trace_hardirqs_on_thunk+0x3a/0x3f
 [<ffffffff8150db5d>] ? retint_swapgs+0x13/0x1b
 [<ffffffff8150db5d>] ? retint_swapgs+0x13/0x1b
 [<ffffffff81082a78>] ? trace_hardirqs_on_caller+0x12d/0x164
 [<ffffffff810a74ce>] ? audit_syscall_entry+0x11c/0x148
 [<ffffffff8125c6ee>] ? trace_hardirqs_on_thunk+0x3a/0x3f
 [<ffffffff81513882>] system_call_fastpath+0x16/0x1b


The issue comes from two recent commits:

commit a4010afef585b7142eb605e3a6e4210c0e1b2957
Author: Jesse Brandeburg [off-list ref]
Date:   Wed Oct 5 07:24:41 2011 +0000
e1000: convert hardware management from timers to threads

and

commit 0ef4eedc2e98edd51cd106e1f6a27178622b7e57
Author: Jesse Brandeburg [off-list ref]
Date:   Wed Oct 5 07:24:51 2011 +0000
e1000: convert to private mutex from rtnl


What we have is on __e1000_shutdown():

	mutex_lock(&adapter->mutex);

	if (netif_running(netdev)) {
		WARN_ON(test_bit(__E1000_RESETTING, &adapter->flags));
		e1000_down(adapter);
	}

but e1000_down() calls: e1000_down_and_stop():

static void e1000_down_and_stop(struct e1000_adapter *adapter)
{
	set_bit(__E1000_DOWN, &adapter->flags);
	cancel_work_sync(&adapter->reset_task);
	cancel_delayed_work_sync(&adapter->watchdog_task);
	cancel_delayed_work_sync(&adapter->phy_info_task);
	cancel_delayed_work_sync(&adapter->fifo_stall_task);
}


Here you see that we are calling cancel_delayed_work_sync(&adapter->watchdog_task);

The problem is that adapter->watchdog_task grabs the mutex &adapter->mutex.

If the work has started and it blocked on that mutex, the
cancel_delayed_work_sync() will block indefinitely and we have a
deadlock.

Not sure what's the best way around this. Can we call e1000_down()
without grabbing the adapter->mutex?

Thanks for the report, I'll look at it today and see if I can work out
a way to avoid the bonk.

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