linux-kernel - Re: [PATCH] kobject: WARN as tip when call kobject

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Date:	Thu, 12 Mar 2015 08:45:09 +0100
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Ethan Zhao <ethan.zhao@...cle.com>
Cc:	linux-kernel@...r.kernel.org, ethan.kernel@...il.com
Subject: Re: [PATCH] kobject: WARN as tip when call kobject_get() to a
 kobject not initialized

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@...cle.com>
> ---
>  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
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...

thanks,

greg k-h
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