usbnet: smsc95xx: Fix deadlock on runtime resume

usbnet: smsc95xx: Fix deadlock on runtime resume

Commit 2bdbf5a23dc6 ("smsc95xx: add phylib support") amended
smsc95xx_resume() to call phy_init_hw().  That function waits for the
device to runtime resume even though it is placed in the runtime resume
path, causing a deadlock.

The problem is that phy_init_hw() calls down to smsc95xx_mdiobus_read(),
which never uses the _nopm variant of usbnet_read_cmd().

Commit 0fe16173902d ("usbnet: smsc95xx: add reset_resume function with
reset operation") causes a similar deadlock on resume if the device was
already runtime suspended when entering system sleep:

That's because the commit introduced smsc95xx_reset_resume(), which
calls down to smsc95xx_reset(), which neglects to use _nopm accessors.

Fix by auto-detecting whether a device access is performed by the
suspend/resume task_struct and use the _nopm variant if so.  This works
because the PM core guarantees that suspend/resume callbacks are run in
task context.

Stacktrace for posterity:

  INFO: task kworker/2:1:49 blocked for more than 122 seconds.
  Workqueue: usb_hub_wq hub_event
  schedule
  rpm_resume
  __pm_runtime_resume
  usb_autopm_get_interface
  usbnet_read_cmd
  __smsc95xx_read_reg
  __smsc95xx_phy_wait_not_busy
  __smsc95xx_mdio_read
  smsc95xx_mdiobus_read
  __mdiobus_read
  mdiobus_read
  smsc_phy_reset
  phy_init_hw
  smsc95xx_resume
  usb_resume_interface
  usb_resume_both
  usb_runtime_resume
  __rpm_callback
  rpm_callback
  rpm_resume
  __pm_runtime_resume
  usb_autoresume_device
  hub_event
  process_one_work

Fixes: 0fe16173902d ("usbnet: smsc95xx: add reset_resume function with reset operation")
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: stable@vger.kernel.org # v3.16+
Cc: Andre Edich <andre.edich@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>