Re: [PATCH v2] software node: balance refcount for managed sw nodes

[Laurentiu Tudor]

On 9/14/2021 5:50 PM, Greg KH wrote:
> On Tue, Sep 14, 2021 at 05:44:09PM +0300, laurentiu.tudor@xxxxxxx wrote:
>> 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>
>> Suggested-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
>> Reviewed-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
>> Signed-off-by: Laurentiu Tudor <laurentiu.tudor@xxxxxxx>
>> ---
>> Changes since v1:
>>  - added Heikki's Reviewed-by: (Thanks!)
>>
>> Changes since RFC:
>>  - use software_node_notify(KOBJ_ADD) instead of directly bumping
>>    refcount (Heikki)
>>
>>  drivers/base/swnode.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
>> index d1f1a8240120..bdb50a06c82a 100644
>> --- a/drivers/base/swnode.c
>> +++ b/drivers/base/swnode.c
>> @@ -1113,6 +1113,9 @@ int device_create_managed_software_node(struct device *dev,
>>  	to_swnode(fwnode)->managed = true;
>>  	set_secondary_fwnode(dev, fwnode);
>>  
>> +	if (device_is_registered(dev))
>> +		software_node_notify(dev, KOBJ_ADD);
>> +
>>  	return 0;
>>  }
>>  EXPORT_SYMBOL_GPL(device_create_managed_software_node);
>> -- 
>> 2.17.1
>>
> 
> I am seeing that this needs to go into 5.15-final, but how about any
> further back?  Stable kernels?  

I think that's a good point. I can resend and Cc: stable if everyone's
fine with that.

> Does this "fix" a specific commit?

I did not found a certain commit that introduced the breakage so don't
know what to say here. I'd let more experienced people comment on this.

---
Best Regards, Laurentiu