Re: [PATCH] kobject: WARN as tip when call kobject_get() to a kobject not initialized

[Ethan Zhao]

On Thu, Mar 12, 2015 at 3:45 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> On Thu, Mar 12, 2015 at 01:04:16PM +0900, Ethan Zhao wrote:
>> call kobject_get() to kojbect that is not initalized or released will only
>> leave following like call trace to us:
>>
>> -----------[ cut here ]------------
>> [   54.545816] WARNING: CPU: 0 PID: 213 at include/linux/kref.h:47
>> kobject_get+0x41/0x50()
>> [   54.642595] Modules linked in: i2c_i801(+) mfd_core shpchp(+)
>> acpi_cpufreq(+) edac_core ioatdma(+) xfs libcrc32c ast syscopyarea ixgbe
>> sysfillrect sysimgblt sr_mod sd_mod drm_kms_helper igb mdio cdrom e1000e ahci
>> dca ttm libahci uas drm i2c_algo_bit ptp megaraid_sas libata usb_storage
>> i2c_core pps_core dm_mirror dm_region_hash dm_log dm_mod
>> [   55.007264] CPU: 0 PID: 213 Comm: kworker/0:2 Not tainted
>> 3.18.5
>> [   55.099970] Hardware name: Oracle Corporation SUN FIRE X4170 M2 SERVER
>>    /ASSY,MOTHERBOARD,X4170, BIOS 08120104 05/08/2012
>> [   55.239736] Workqueue: kacpi_notify acpi_os_execute_deferred
>> [   55.308598]  0000000000000000 00000000bd730b61 ffff88046742baf8
>> ffffffff816b7edb
>> [   55.398305]  0000000000000000 0000000000000000 ffff88046742bb38
>> ffffffff81078ae1
>> [   55.488040]  ffff88046742bbd8 ffff8806706b3000 0000000000000292
>> 0000000000000000
>> [   55.577776] Call Trace:
>> [   55.608228]  [<ffffffff816b7edb>] dump_stack+0x46/0x58
>> [   55.670895]  [<ffffffff81078ae1>] warn_slowpath_common+0x81/0xa0
>> [   55.743952]  [<ffffffff81078bfa>] warn_slowpath_null+0x1a/0x20
>> [   55.814929]  [<ffffffff8130d0d1>] kobject_get+0x41/0x50
>> [   55.878654]  [<ffffffff8153e955>] cpufreq_cpu_get+0x75/0xc0
>> [   55.946528]  [<ffffffff8153f37e>] cpufreq_update_policy+0x2e/0x1f0
>>
>> The above issue was casued by a race condition, if there is a WARN in
>> kobject_get() of the kobject is not initialized, that would save us much
>> time to debug it.
>>
>> Signed-off-by: Ethan Zhao <ethan.zhao@xxxxxxxxxx>
>> ---
>>  lib/kobject.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/kobject.c b/lib/kobject.c
>> index 03d4ab3..3b841b9 100644
>> --- a/lib/kobject.c
>> +++ b/lib/kobject.c
>> @@ -576,8 +576,13 @@ void kobject_del(struct kobject *kobj)
>>   */
>>  struct kobject *kobject_get(struct kobject *kobj)
>>  {
>> -     if (kobj)
>> +     if (kobj) {
>> +             if (!kobj->state_initialized)
>> +                     WARN(1, KERN_WARNING "kobject: '%s' (%p): is not "
>> +                            "initialized, yet kobject_get() is being "
>> +                            "called.\n", kobject_name(kobj), kobj);
>>               kref_get(&kobj->kref);
>> +     }
>>       return kobj;
>>  }
>>
>
> Have you tried running a system with this patch to see if there are a
> lot of messages at boot time?  I'm a bit worried that the initial

Don't worry about that, no warning appear if no bug hit, I have tried
booting the kernel with this patch hundreds of times (To verify another
issue at the same time ).

> kobject init sequence would trigger this, but haven't looked at the full
> codepath just yet given that I haven't had my morning coffee...

 Enjoy your coffee.


Thanks,
Ethan
>
> thanks,
>
> greg k-h
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