[RFC PATCH] software node: balance refcount for managed sw nodes

[laurentiu . tudor]

From: Laurentiu Tudor <laurentiu.tudor@xxxxxxx>

software_node_notify(), on KOBJ_REMOVE drops the refcount twice on managed
software nodes, thus leading to underflow errors. Balance the refcount by
bumping it in the device_create_managed_software_node() function.

The error [1] was encountered after adding a .shutdown() op to our
fsl-mc-bus driver.

[1]
pc : refcount_warn_saturate+0xf8/0x150
lr : refcount_warn_saturate+0xf8/0x150
sp : ffff80001009b920
x29: ffff80001009b920 x28: ffff1a2420318000 x27: 0000000000000000
x26: ffffccac15e7a038 x25: 0000000000000008 x24: ffffccac168e0030
x23: ffff1a2428a82000 x22: 0000000000080000 x21: ffff1a24287b5000
x20: 0000000000000001 x19: ffff1a24261f4400 x18: ffffffffffffffff
x17: 6f72645f726f7272 x16: 0000000000000000 x15: ffff80009009b607
x14: 0000000000000000 x13: ffffccac16602670 x12: 0000000000000a17
x11: 000000000000035d x10: ffffccac16602670 x9 : ffffccac16602670
x8 : 00000000ffffefff x7 : ffffccac1665a670 x6 : ffffccac1665a670
x5 : 0000000000000000 x4 : 0000000000000000 x3 : 00000000ffffffff
x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff1a2420318000
Call trace:
 refcount_warn_saturate+0xf8/0x150
 kobject_put+0x10c/0x120
 software_node_notify+0xd8/0x140
 device_platform_notify+0x4c/0xb4
 device_del+0x188/0x424
 fsl_mc_device_remove+0x2c/0x4c
 rebofind sp.c__fsl_mc_device_remove+0x14/0x2c
 device_for_each_child+0x5c/0xac
 dprc_remove+0x9c/0xc0
 fsl_mc_driver_remove+0x28/0x64
 __device_release_driver+0x188/0x22c
 device_release_driver+0x30/0x50
 bus_remove_device+0x128/0x134
 device_del+0x16c/0x424
 fsl_mc_bus_remove+0x8c/0x114
 fsl_mc_bus_shutdown+0x14/0x20
 platform_shutdown+0x28/0x40
 device_shutdown+0x15c/0x330
 __do_sys_reboot+0x218/0x2a0
 __arm64_sys_reboot+0x28/0x34
 invoke_syscall+0x48/0x114
 el0_svc_common+0x40/0xdc
 do_el0_svc+0x2c/0x94
 el0_svc+0x2c/0x54
 el0t_64_sync_handler+0xa8/0x12c
 el0t_64_sync+0x198/0x19c
---[ end trace 32eb1c71c7d86821 ]---

Reported-by: Jon Nettleton <jon@xxxxxxxxxxxxx>
Signed-off-by: Laurentiu Tudor <laurentiu.tudor@xxxxxxx>
---
 drivers/base/swnode.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
index d1f1a8240120..907616ca487f 100644
--- a/drivers/base/swnode.c
+++ b/drivers/base/swnode.c
@@ -1113,6 +1113,8 @@ int device_create_managed_software_node(struct device *dev,
 	to_swnode(fwnode)->managed = true;
 	set_secondary_fwnode(dev, fwnode);
 
+	kobject_get(&to_swnode(fwnode)->kobj);
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(device_create_managed_software_node);
-- 
2.17.1