Commit 14b41a29

 ("net: stmmac: Delete txtimer in suspend") was the
first attempt to fix a race between mod_timer() and setup_timer()
during stmmac_resume(). However the issue still exists as the commit
only addressed half of the issue.

Same race can still happen as stmmac_resume() re-attaches interface
way too early - even before hardware is fully initialized.  Worse,
doing so allows network traffic to restart and stmmac_tx_timer_arm()
being called in the middle of stmmac_resume(), which re-init tx timers
in stmmac_init_coalesce().  timer_list will be corrupted and system
crashes as a result of race between mod_timer() and setup_timer().

  systemd--1995    2.... 552950018us : stmmac_suspend: 4994
  ksoftirq-9       0..s2 553123133us : stmmac_tx_timer_arm: 2276
  systemd--1995    0.... 553127896us : stmmac_resume: 5101
  systemd--320     7...2 553132752us : stmmac_tx_timer_arm: 2276
  (sd-exec-1999    5...2 553135204us : stmmac_tx_timer_arm: 2276
  ---------------------------------
  pc : run_timer_softirq+0x468/0x5e0
  lr : run_timer_softirq+0x570/0x5e0
  Call trace:
   run_timer_softirq+0x468/0x5e0
   __do_softirq+0x124/0x398
   irq_exit+0xd8/0xe0
   __handle_domain_irq+0x6c/0xc0
   gic_handle_irq+0x60/0xb0
   el1_irq+0xb8/0x180
   arch_cpu_idle+0x38/0x230
   default_idle_call+0x24/0x3c
   do_idle+0x1e0/0x2b8
   cpu_startup_entry+0x28/0x48
   secondary_start_kernel+0x1b4/0x208

Fix this by deferring netif_device_attach() to the end of
stmmac_resume().

Signed-off-by: Leon Yu <leoyu@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>