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

[Ethan Zhao]

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;
 }
 
-- 
1.8.3.1

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