phylib: Fix deadlock on resume

Sometimes kernel hangs on resume with the following trace:

 ucc_geth e0102000.ucc: resume
 INFO: task bash:1764 blocked for more than 120 seconds.
 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
 bash          D 0fecf43c     0  1764   1763 0x00000000
 Call Trace:
 [cf9a7c10] [c0012868] ret_from_except+0x0/0x14 (unreliable)
 --- Exception: cf9a7ce0 at __switch_to+0x4c/0x6c
     LR = 0xcf9a7cc0
 [cf9a7cd0] [c0008c14] __switch_to+0x4c/0x6c (unreliable)
 [cf9a7ce0] [c028bcfc] schedule+0x158/0x260
 [cf9a7d10] [c028c720] __mutex_lock_slowpath+0x80/0xd8
 [cf9a7d40] [c01cf388] phy_stop+0x20/0x70
 [cf9a7d50] [c01d514c] ugeth_resume+0x6c/0x13c
 [...]

Here is why.

On suspend:

- PM core starts suspending devices, ucc_geth_suspend gets called;

- ucc_geth calls phy_stop() on suspend. Note that phy_stop() is
  mostly asynchronous so it doesn't block ucc_geth's suspend routine,
  it just sets PHY_HALTED state and disables PHY's interrupts;

- Suddenly the state machine gets scheduled, it grabs the phydev->lock
  mutex and tries to process the PHY_HALTED state, so it calls
  phydev->adjust_link(phydev->attached_dev). In ucc_geth case
  adjust_link() calls msleep(), which reschedules the code flow back to
  PM core, which now finishes suspend and so we end up sleeping with
  phydev->lock mutex held.

On resume:

- PM core starts resuming devices (notice that nobody rescheduled
  the state machine yet, so the mutex is still held), the core calls
  ucc_geth's resume routine;

- ucc_geth_resume restarts the PHY with phy_stop()/phy_start()
  sequence, and the phy_*() calls are trying to grab the phydev->lock
  mutex. Here comes the deadlock.

This patch fixes the issue by stopping the state machine on suspend
and starting it again on resume.
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/mdio_bus.c

@@ -303,8 +303,18 @@ static int mdio_bus_suspend(struct device * dev, pm_message_t state)
 	struct phy_driver *phydrv = to_phy_driver(dev->driver);
 	struct phy_device *phydev = to_phy_device(dev);
 
+	/*
+	 * We must stop the state machine manually, otherwise it stops out of
+	 * control, possibly with the phydev->lock held. Upon resume, netdev
+	 * may call phy routines that try to grab the same lock, and that may
+	 * lead to a deadlock.
+	 */
+	if (phydev->attached_dev)
+		phy_stop_machine(phydev);
+
 	if (!mdio_bus_phy_may_suspend(phydev))
 		return 0;
+
 	return phydrv->suspend(phydev);
 }
 
@@ -312,10 +322,20 @@ static int mdio_bus_resume(struct device * dev)
 {
 	struct phy_driver *phydrv = to_phy_driver(dev->driver);
 	struct phy_device *phydev = to_phy_device(dev);
+	int ret;
 
 	if (!mdio_bus_phy_may_suspend(phydev))
-		return 0;
-	return phydrv->resume(phydev);
+		goto no_resume;
+
+	ret = phydrv->resume(phydev);
+	if (ret < 0)
+		return ret;
+
+no_resume:
+	if (phydev->attached_dev)
+		phy_start_machine(phydev, NULL);
+
+	return 0;
 }
 
 struct bus_type mdio_bus_type = {