From: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
When LAN9303 is MDIO-connected two callchains exist into
mdio->bus->write():
1. switch ports 1&2 ("physical" PHYs):
virtual (switch-internal) MDIO bus (lan9303_switch_ops->phy_{read|write})->
lan9303_mdio_phy_{read|write} -> mdiobus_{read|write}_nested
2. LAN9303 virtual PHY:
virtual MDIO bus (lan9303_phy_{read|write}) ->
lan9303_virt_phy_reg_{read|write} -> regmap -> lan9303_mdio_{read|write}
If the latter functions just take
mutex_lock(&sw_dev->device->bus->mdio_lock) it triggers a LOCKDEP
false-positive splat. It's false-positive because the first
mdio_lock in the second callchain above belongs to virtual MDIO bus, the
second mdio_lock belongs to physical MDIO bus.
Consequent annotation in lan9303_mdio_{read|write} as nested lock
(similar to lan9303_mdio_phy_{read|write}, it's the same physical MDIO bus)
prevents the following splat:
WARNING: possible circular locking dependency detected
5.15.71 #1 Not tainted
------------------------------------------------------
kworker/u4:3/609 is trying to acquire lock:
ffff000011531c68 (lan9303_mdio:131:(&lan9303_mdio_regmap_config)->lock){+.+.}-{3:3}, at: regmap_lock_mutex
but task is already holding lock:
ffff0000114c44d8 (&bus->mdio_lock){+.+.}-{3:3}, at: mdiobus_read
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&bus->mdio_lock){+.+.}-{3:3}:
lock_acquire
__mutex_lock
mutex_lock_nested
lan9303_mdio_read
_regmap_read
regmap_read
lan9303_probe
lan9303_mdio_probe
mdio_probe
really_probe
__driver_probe_device
driver_probe_device
__device_attach_driver
bus_for_each_drv
__device_attach
device_initial_probe
bus_probe_device
deferred_probe_work_func
process_one_work
worker_thread
kthread
ret_from_fork
-> #0 (lan9303_mdio:131:(&lan9303_mdio_regmap_config)->lock){+.+.}-{3:3}:
__lock_acquire
lock_acquire.part.0
lock_acquire
__mutex_lock
mutex_lock_nested
regmap_lock_mutex
regmap_read
lan9303_phy_read
dsa_slave_phy_read
__mdiobus_read
mdiobus_read
get_phy_device
mdiobus_scan
__mdiobus_register
dsa_register_switch
lan9303_probe
lan9303_mdio_probe
mdio_probe
really_probe
__driver_probe_device
driver_probe_device
__device_attach_driver
bus_for_each_drv
__device_attach
device_initial_probe
bus_probe_device
deferred_probe_work_func
process_one_work
worker_thread
kthread
ret_from_fork
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&bus->mdio_lock);
lock(lan9303_mdio:131:(&lan9303_mdio_regmap_config)->lock);
lock(&bus->mdio_lock);
lock(lan9303_mdio:131:(&lan9303_mdio_regmap_config)->lock);
*** DEADLOCK ***
5 locks held by kworker/u4:3/609:
#0: ffff000002842938 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work
#1: ffff80000bacbd60 (deferred_probe_work){+.+.}-{0:0}, at: process_one_work
#2: ffff000007645178 (&dev->mutex){....}-{3:3}, at: __device_attach
#3: ffff8000096e6e78 (dsa2_mutex){+.+.}-{3:3}, at: dsa_register_switch
#4: ffff0000114c44d8 (&bus->mdio_lock){+.+.}-{3:3}, at: mdiobus_read
stack backtrace:
CPU: 1 PID: 609 Comm: kworker/u4:3 Not tainted 5.15.71 #1
Workqueue: events_unbound deferred_probe_work_func
Call trace:
dump_backtrace
show_stack
dump_stack_lvl
dump_stack
print_circular_bug
check_noncircular
__lock_acquire
lock_acquire.part.0
lock_acquire
__mutex_lock
mutex_lock_nested
regmap_lock_mutex
regmap_read
lan9303_phy_read
dsa_slave_phy_read
__mdiobus_read
mdiobus_read
get_phy_device
mdiobus_scan
__mdiobus_register
dsa_register_switch
lan9303_probe
lan9303_mdio_probe
...
Cc: stable@xxxxxxxxxxxxxxx
Fixes: dc7005831523 ("net: dsa: LAN9303: add MDIO managed mode support")
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
---
Tested with v5.15 vendor kernel, compiled against net-next/main
(cc54d2e2c58a). Affected code is unchanged since original introduction in
2017.
drivers/net/dsa/lan9303_mdio.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/net/dsa/lan9303_mdio.c b/drivers/net/dsa/lan9303_mdio.c
index d8ab2b77d201..167a86f39f27 100644
--- a/drivers/net/dsa/lan9303_mdio.c
+++ b/drivers/net/dsa/lan9303_mdio.c
@@ -32,7 +32,7 @@ static int lan9303_mdio_write(void *ctx, uint32_t reg, uint32_t val)
struct lan9303_mdio *sw_dev = (struct lan9303_mdio *)ctx;
reg <<= 2; /* reg num to offset */
- mutex_lock(&sw_dev->device->bus->mdio_lock);
+ mutex_lock_nested(&sw_dev->device->bus->mdio_lock, MDIO_MUTEX_NESTED);
lan9303_mdio_real_write(sw_dev->device, reg, val & 0xffff);
lan9303_mdio_real_write(sw_dev->device, reg + 2, (val >> 16) & 0xffff);
mutex_unlock(&sw_dev->device->bus->mdio_lock);
@@ -50,7 +50,7 @@ static int lan9303_mdio_read(void *ctx, uint32_t reg, uint32_t *val)
struct lan9303_mdio *sw_dev = (struct lan9303_mdio *)ctx;
reg <<= 2; /* reg num to offset */
- mutex_lock(&sw_dev->device->bus->mdio_lock);
+ mutex_lock_nested(&sw_dev->device->bus->mdio_lock, MDIO_MUTEX_NESTED);
*val = lan9303_mdio_real_read(sw_dev->device, reg);
*val |= (lan9303_mdio_real_read(sw_dev->device, reg + 2) << 16);
mutex_unlock(&sw_dev->device->bus->mdio_lock);
--
2.41.0
