net:phy: fix deadlocking in phy_error() invocation

Backported from linux-6.7.0,  commit a0e026e7b37e997f4fa3fcaa714e5484f3ce9e75
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/net/phy/phy.c?id=a0e026e7b37e997f4fa3fcaa714e5484f3ce9e75

Since commit 91a7cda1f4b8 ("net: phy: Fix race condition on link status
change") all the phy_error() method invocations have been causing the
nested-mutex-lock deadlock because it's normally done in the PHY-driver
threaded IRQ handlers which since that change have been called with the
phydev->lock mutex held. Here is the calls thread:

IRQ: phy_interrupt()
     +-> mutex_lock(&phydev->lock); <--------------------+
         drv->handle_interrupt()                         | Deadlock due
         +-> ERROR: phy_error()                          + to the nested
                    +-> phy_process_error()              | mutex lock
                        +-> mutex_lock(&phydev->lock); <-+
                            phydev->state = PHY_ERROR;
                            mutex_unlock(&phydev->lock);
         mutex_unlock(&phydev->lock);

The problem can be easily reproduced just by calling phy_error() from any
PHY-device threaded interrupt handler. Fix it by dropping the phydev->lock
mutex lock from the phy_process_error() method and printing a nasty error
message to the system log if the mutex isn't held in the caller execution
context.

Note for the fix to work correctly in the PHY-subsystem itself the
phydev->lock mutex locking must be added to the phy_error_precise()
function.

Link: https://lore.kernel.org/netdev/20230816180944.19262-1-fancer.lancer@gmail.com


Fixes: 91a7cda1f4b8 ("net: phy: Fix race condition on link status change")
Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

Signed-off-by: Mikhail Vanyulin <mikhail.vanyulin@rtsoft.de>

drivers/net/phy/phy.c

@@ -941,9 +941,10 @@ void phy_error(struct phy_device *phydev)
 {
 	WARN_ON(1);
 
-	mutex_lock(&phydev->lock);
+	/* phydev->lock must be held for the state change to be safe */
+	if (!mutex_is_locked(&phydev->lock))
+		phydev_err(phydev, "PHY-device data unsafe context\n");
 	phydev->state = PHY_HALTED;
-	mutex_unlock(&phydev->lock);
 
 	phy_trigger_machine(phydev);
 }