[PATCH AUTOSEL 5.0 093/262] net: dsa: mv88e6xxx: Add lockdep classes to fix false positive splat

Sasha Levin
2019-03-27T18:04:56Z

From: Andrew Lunn <andrew@lunn.ch>

[ Upstream commit f6d9758b12660484b6639364cc406da92a918c96 ]

The following false positive lockdep splat has been observed.

======================================================
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);

&desc->request_mutex refer to two different mutex. #1 is the GPIO for
the chip interrupt. #2 is the chained interrupt between global 1 and
global 2.

Add lockdep classes to the GPIO interrupt to avoid this.

Reported-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/dsa/mv88e6xxx/chip.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 4a0ec8e87c7a..6cba05a80892 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -442,12 +442,20 @@ static int mv88e6xxx_g1_irq_setup_common(struct mv88e6xxx_chip *chip)

static int mv88e6xxx_g1_irq_setup(struct mv88e6xxx_chip *chip)
{
+ static struct lock_class_key lock_key;
+ static struct lock_class_key request_key;
int err;

err = mv88e6xxx_g1_irq_setup_common(chip);
if (err)
return err;

+ /* These lock classes tells lockdep that global 1 irqs are in
+ * a different category than their parent GPIO, so it won't
+ * report false recursion.
+ */
+ irq_set_lockdep_class(chip->irq, &lock_key, &request_key);
+
err = request_threaded_irq(chip->irq, NULL,
mv88e6xxx_g1_irq_thread_fn,
IRQF_ONESHOT | IRQF_SHARED,
--
2.19.1