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Subject: Re: [RFC PATCH] software node: balance refcount for managed sw nodes
To:     Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc:     andriy.shevchenko@linux.intel.com, gregkh@linuxfoundation.org,
        rafael@kernel.org, linux-acpi@vger.kernel.org,
        linux-kernel@vger.kernel.org, jon@solid-run.com
References: <20210716081711.7638-1-laurentiu.tudor@nxp.com>
 <YPFSHiHZzjwJD2PI@kuha.fi.intel.com>
From:   Laurentiu Tudor <laurentiu.tudor@nxp.com>
Message-ID: <54836f5e-8180-2bfe-58be-7e232ab42f1e@nxp.com>
Date:   Fri, 16 Jul 2021 13:09:55 +0300
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On 7/16/2021 12:32 PM, Heikki Krogerus wrote:
> Fri, Jul 16, 2021 at 11:17:11AM +0300, laurentiu.tudor@nxp.com kirjoitti:
>> From: Laurentiu Tudor <laurentiu.tudor@nxp.com>
>>
>> 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@solid-run.com>
>> Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
>> ---
>>  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);
> 
> We can't increment the refcount uncoditionally like that. Would this
> work instead:
> 

It works, thanks for the suggestion! I'll return with a non-RFC right away.

---
Best Regards, Laurentiu