[PATCH net] net: dsa: fix lockdep warning

[Russell King <rmk+kernel@armlinux.org.uk>]

======================================================
WARNING: possible circular locking dependency detected
4.20.0+ #302 Not tainted
------------------------------------------------------
systemd-udevd/160 is trying to acquire lock:
edea6080 (&chip->reg_lock){+.+.}, at: __setup_irq+0x640/0x704

but task is already holding lock:
edff0340 (&desc->request_mutex){+.+.}, at: __setup_irq+0xa0/0x704

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&desc->request_mutex){+.+.}:
       mutex_lock_nested+0x1c/0x24
       __setup_irq+0xa0/0x704
       request_threaded_irq+0xd0/0x150
       mv88e6xxx_probe+0x41c/0x694 [mv88e6xxx]
       mdio_probe+0x2c/0x54
       really_probe+0x200/0x2c4
       driver_probe_device+0x5c/0x174
       __driver_attach+0xd8/0xdc
       bus_for_each_dev+0x58/0x7c
       bus_add_driver+0xe4/0x1f0
       driver_register+0x7c/0x110
       mdio_driver_register+0x24/0x58
       do_one_initcall+0x74/0x2e8
       do_init_module+0x60/0x1d0
       load_module+0x1968/0x1ff4
       sys_finit_module+0x8c/0x98
       ret_fast_syscall+0x0/0x28
       0xbedf2ae8

-> #0 (&chip->reg_lock){+.+.}:
       __mutex_lock+0x50/0x8b8
       mutex_lock_nested+0x1c/0x24
       __setup_irq+0x640/0x704
       request_threaded_irq+0xd0/0x150
       mv88e6xxx_g2_irq_setup+0xcc/0x1b4 [mv88e6xxx]
       mv88e6xxx_probe+0x44c/0x694 [mv88e6xxx]
       mdio_probe+0x2c/0x54
       really_probe+0x200/0x2c4
       driver_probe_device+0x5c/0x174
       __driver_attach+0xd8/0xdc
       bus_for_each_dev+0x58/0x7c
       bus_add_driver+0xe4/0x1f0
       driver_register+0x7c/0x110
       mdio_driver_register+0x24/0x58
       do_one_initcall+0x74/0x2e8
       do_init_module+0x60/0x1d0
       load_module+0x1968/0x1ff4
       sys_finit_module+0x8c/0x98
       ret_fast_syscall+0x0/0x28
       0xbedf2ae8

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&desc->request_mutex);
                               lock(&chip->reg_lock);
                               lock(&desc->request_mutex);
  lock(&chip->reg_lock);

 *** DEADLOCK ***

2 locks held by systemd-udevd/160:
 #0: ee040868 (&dev->mutex){....}, at: __driver_attach+0x70/0xdc
 #1: edff0340 (&desc->request_mutex){+.+.}, at: __setup_irq+0xa0/0x704

stack backtrace:
CPU: 1 PID: 160 Comm: systemd-udevd Not tainted 4.20.0+ #302
Hardware name: Marvell Armada 380/385 (Device Tree)
[<c0019638>] (unwind_backtrace) from [<c0014888>] (show_stack+0x10/0x14)
[<c0014888>] (show_stack) from [<c07f54e0>] (dump_stack+0x9c/0xd4)
[<c07f54e0>] (dump_stack) from [<c0088afc>] (print_circular_bug+0x284/0x2d8)
[<c0088afc>] (print_circular_bug) from [<c0086b5c>] (__lock_acquire+0x15d4/0x19b8)
[<c0086b5c>] (__lock_acquire) from [<c0087828>] (lock_acquire+0xc4/0x1dc)
[<c0087828>] (lock_acquire) from [<c080fd88>] (__mutex_lock+0x50/0x8b8)
[<c080fd88>] (__mutex_lock) from [<c0810678>] (mutex_lock_nested+0x1c/0x24)
[<c0810678>] (mutex_lock_nested) from [<c009e060>] (__setup_irq+0x640/0x704)
[<c009e060>] (__setup_irq) from [<c009e2e0>] (request_threaded_irq+0xd0/0x150)
[<c009e2e0>] (request_threaded_irq) from [<bf0ce978>] (mv88e6xxx_g2_irq_setup+0xcc/0x1b4 [mv88e6xxx])
[<bf0ce978>] (mv88e6xxx_g2_irq_setup [mv88e6xxx]) from [<bf0c7ab0>] (mv88e6xxx_probe+0x44c/0x694 [mv88e6xxx])
[<bf0c7ab0>] (mv88e6xxx_probe [mv88e6xxx]) from [<c050d420>] (mdio_probe+0x2c/0x54)
[<c050d420>] (mdio_probe) from [<c0496eac>] (really_probe+0x200/0x2c4)
[<c0496eac>] (really_probe) from [<c0497140>] (driver_probe_device+0x5c/0x174)
[<c0497140>] (driver_probe_device) from [<c0497330>] (__driver_attach+0xd8/0xdc)
[<c0497330>] (__driver_attach) from [<c0495494>] (bus_for_each_dev+0x58/0x7c)
[<c0495494>] (bus_for_each_dev) from [<c04963d4>] (bus_add_driver+0xe4/0x1f0)
[<c04963d4>] (bus_add_driver) from [<c0498038>] (driver_register+0x7c/0x110)
[<c0498038>] (driver_register) from [<c050d338>] (mdio_driver_register+0x24/0x58)
[<c050d338>] (mdio_driver_register) from [<c000afdc>] (do_one_initcall+0x74/0x2e8)
[<c000afdc>] (do_one_initcall) from [<c00d4994>] (do_init_module+0x60/0x1d0)
[<c00d4994>] (do_init_module) from [<c00d39e0>] (load_module+0x1968/0x1ff4)
mvneta f1034000.ethernet eth2: requesting inband/2500base-x, 00200,0000a440
[<c00d39e0>] (load_module) from [<c00d4248>] (sys_finit_module+0x8c/0x98)
[<c00d4248>] (sys_finit_module) from [<c0009000>] (ret_fast_syscall+0x0/0x28)
Exception stack(0xedfe5fa8 to 0xedfe5ff0)
5fa0:                   00020000 00000000 0000000b b6f2a4b5 00000000 00b8fc70
5fc0: 00020000 00000000 00000000 0000017b 00b995a0 00020000 00000000 00b8fc70
5fe0: bedf2af8 bedf2ae8 b6f242ac b6e83d70

This is caused by the locking order inversion in mv88e6xxx_probe:

        mutex_lock(&chip->reg_lock);
        if (chip->irq > 0)
                err = mv88e6xxx_g1_irq_setup(chip);
        else
                err = mv88e6xxx_irq_poll_setup(chip);
        mutex_unlock(&chip->reg_lock);

Here, we take chip->reg_lock, and then call into mv88e6xxx_g1_irq_setup()
which then calls request_threaded_irq(), taking the request_mutex.

However, when we request the g2 interrupt, we call request_threaded_irq()
again, which takes the request_mutex, which then goes on to call
chip_bus_lock().  This comes through to mv88e6xxx_g1_irq_bus_lock,
which then tries to grab chip->reg_lock.  This results in the two locks
being taken together in differing orders, provoking lockdep to warn.

Move the mutex_lock()/unlock() for reg_lock inside
mv88e6xxx_g1_irq_free_common() and mv88e6xxx_g1_irq_setup_common(), where
we actually access registers, thereby avoiding holding it while calling
request_threaded_irq() or setting up the delayed work.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 24fb6a685039..801442195a04 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -349,9 +349,11 @@ static void mv88e6xxx_g1_irq_free_common(struct mv88e6xxx_chip *chip)
 	int irq, virq;
 	u16 mask;
 
+	mutex_lock(&chip->reg_lock);
 	mv88e6xxx_g1_read(chip, MV88E6XXX_G1_CTL1, &mask);
 	mask &= ~GENMASK(chip->g1_irq.nirqs, 0);
 	mv88e6xxx_g1_write(chip, MV88E6XXX_G1_CTL1, mask);
+	mutex_unlock(&chip->reg_lock);
 
 	for (irq = 0; irq < chip->g1_irq.nirqs; irq++) {
 		virq = irq_find_mapping(chip->g1_irq.domain, irq);
@@ -369,9 +371,7 @@ static void mv88e6xxx_g1_irq_free(struct mv88e6xxx_chip *chip)
 	 */
 	free_irq(chip->irq, chip);
 
-	mutex_lock(&chip->reg_lock);
 	mv88e6xxx_g1_irq_free_common(chip);
-	mutex_unlock(&chip->reg_lock);
 }
 
 static int mv88e6xxx_g1_irq_setup_common(struct mv88e6xxx_chip *chip)
@@ -392,6 +392,7 @@ static int mv88e6xxx_g1_irq_setup_common(struct mv88e6xxx_chip *chip)
 	chip->g1_irq.chip = mv88e6xxx_g1_irq_chip;
 	chip->g1_irq.masked = ~0;
 
+	mutex_lock(&chip->reg_lock);
 	err = mv88e6xxx_g1_read(chip, MV88E6XXX_G1_CTL1, &mask);
 	if (err)
 		goto out_mapping;
@@ -406,6 +407,7 @@ static int mv88e6xxx_g1_irq_setup_common(struct mv88e6xxx_chip *chip)
 	err = mv88e6xxx_g1_read(chip, MV88E6XXX_G1_STS, &reg);
 	if (err)
 		goto out_disable;
+	mutex_unlock(&chip->reg_lock);
 
 	return 0;
 
@@ -414,6 +416,7 @@ static int mv88e6xxx_g1_irq_setup_common(struct mv88e6xxx_chip *chip)
 	mv88e6xxx_g1_write(chip, MV88E6XXX_G1_CTL1, mask);
 
 out_mapping:
+	mutex_unlock(&chip->reg_lock);
 	for (irq = 0; irq < 16; irq++) {
 		virq = irq_find_mapping(chip->g1_irq.domain, irq);
 		irq_dispose_mapping(virq);
@@ -479,9 +482,7 @@ static void mv88e6xxx_irq_poll_free(struct mv88e6xxx_chip *chip)
 	kthread_cancel_delayed_work_sync(&chip->irq_poll_work);
 	kthread_destroy_worker(chip->kworker);
 
-	mutex_lock(&chip->reg_lock);
 	mv88e6xxx_g1_irq_free_common(chip);
-	mutex_unlock(&chip->reg_lock);
 }
 
 int mv88e6xxx_wait(struct mv88e6xxx_chip *chip, int addr, int reg, u16 mask)
@@ -4718,12 +4719,10 @@ static int mv88e6xxx_probe(struct mdio_device *mdiodev)
 	 * the PHYs will link their interrupts to these interrupt
 	 * controllers
 	 */
-	mutex_lock(&chip->reg_lock);
 	if (chip->irq > 0)
 		err = mv88e6xxx_g1_irq_setup(chip);
 	else
 		err = mv88e6xxx_irq_poll_setup(chip);
-	mutex_unlock(&chip->reg_lock);
 
 	if (err)
 		goto out;
-- 
2.7.4