cxgb3: Missing rtnl lock in error recovery

When exercising error injection on IBM pseries machine, I hit the
following warning:

[  251.450043] RTAS: event: 89, Type: Platform Error, Severity: 2
[  253.549822] cxgb3 0006:01:00.0: enabling device (0140 -> 0142)
[  253.713560] cxgb3 0006:01:00.0: adapter recovering, PEX ERR 0x100
[  254.895437] RTNL: assertion failed at net/core/dev.c (2031)
[  254.895467] CPU: 6 PID: 5449 Comm: eehd Tainted: G        W    3.10.0-rc7-00157-gea461abf #19
[  254.895474] Call Trace:
[  254.895483] [c000000fac56f7d0] [c000000000014dcc] .show_stack+0x7c/0x1f0 (unreliable)
[  254.895493] [c000000fac56f8a0] [c0000000007ba318] .dump_stack+0x28/0x3c
[  254.895500] [c000000fac56f910] [c0000000006c0384] .netif_set_real_num_tx_queues+0x224/0x230
[  254.895515] [c000000fac56f9b0] [d00000000ef35510] .cxgb_open+0x80/0x3f0 [cxgb3]
[  254.895525] [c000000fac56fa50] [d00000000ef35914] .t3_resume_ports+0x94/0x100 [cxgb3]
[  254.895533] [c000000fac56fae0] [c00000000005fc8c] .eeh_report_resume+0x8c/0xd0
[  254.895539] [c000000fac56fb60] [c00000000005e9fc] .eeh_pe_dev_traverse+0x9c/0x190
[  254.895545] [c000000fac56fc10] [c000000000060000] .eeh_handle_event+0x110/0x330
[  254.895551] [c000000fac56fca0] [c000000000060350] .eeh_event_handler+0x130/0x1a0
[  254.895558] [c000000fac56fd30] [c0000000000ad758] .kthread+0xe8/0xf0
[  254.895566] [c000000fac56fe30] [c00000000000a05c] .ret_from_kernel_thread+0x5c/0x80

It appears that t3_resume_ports() is called with the rtnl_lock held from
the fatal error task but not from the PCI error callbacks. This fixes it.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/cxgb3/cxgb3_main.c

@@ -3037,7 +3037,9 @@ static void t3_io_resume(struct pci_dev *pdev)
 	CH_ALERT(adapter, "adapter recovering, PEX ERR 0x%x\n",
 		 t3_read_reg(adapter, A_PCIE_PEX_ERR));
 
+	rtnl_lock();
 	t3_resume_ports(adapter);
+	rtnl_unlock();
 }
 
 static const struct pci_error_handlers t3_err_handler = {