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Subject: Re: [PATCH 5.10 033/306] cpufreq: schedutil: Use kobject release()
 method to free sugov_tunables
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Kevin Hao <haokexin@gmail.com>,
        Viresh Kumar <viresh.kumar@linaro.org>
References: <20210916155753.903069397@linuxfoundation.org>
 <20210916155755.075805845@linuxfoundation.org>
 <bb93bcd1-b9b3-fc11-0321-7be6eee5beb0@intel.com> <YUN89bXPrsLsTAYB@kroah.com>
From:   Alexey Khoroshilov <khoroshilov@ispras.ru>
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Message-ID: <175d4888-1147-9a2f-32d6-7c90c2628af5@ispras.ru>
Date:   Sun, 19 Sep 2021 21:36:20 +0300
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On 16.09.2021 20:20, Greg Kroah-Hartman wrote:
> On Thu, Sep 16, 2021 at 06:12:44PM +0200, Rafael J. Wysocki wrote:
>> On 9/16/2021 5:56 PM, Greg Kroah-Hartman wrote:
>>> From: Kevin Hao <haokexin@gmail.com>
>>>
>>> commit e5c6b312ce3cc97e90ea159446e6bfa06645364d upstream.
>>>
>>> The struct sugov_tunables is protected by the kobject, so we can't free
>>> it directly. Otherwise we would get a call trace like this:
>>>    ODEBUG: free active (active state 0) object type: timer_list hint: delayed_work_timer_fn+0x0/0x30
>>>    WARNING: CPU: 3 PID: 720 at lib/debugobjects.c:505 debug_print_object+0xb8/0x100
>>>    Modules linked in:
>>>    CPU: 3 PID: 720 Comm: a.sh Tainted: G        W         5.14.0-rc1-next-20210715-yocto-standard+ #507
>>>    Hardware name: Marvell OcteonTX CN96XX board (DT)
>>>    pstate: 40400009 (nZcv daif +PAN -UAO -TCO BTYPE=--)
>>>    pc : debug_print_object+0xb8/0x100
>>>    lr : debug_print_object+0xb8/0x100
>>>    sp : ffff80001ecaf910
>>>    x29: ffff80001ecaf910 x28: ffff00011b10b8d0 x27: ffff800011043d80
>>>    x26: ffff00011a8f0000 x25: ffff800013cb3ff0 x24: 0000000000000000
>>>    x23: ffff80001142aa68 x22: ffff800011043d80 x21: ffff00010de46f20
>>>    x20: ffff800013c0c520 x19: ffff800011d8f5b0 x18: 0000000000000010
>>>    x17: 6e6968207473696c x16: 5f72656d6974203a x15: 6570797420746365
>>>    x14: 6a626f2029302065 x13: 303378302f307830 x12: 2b6e665f72656d69
>>>    x11: ffff8000124b1560 x10: ffff800012331520 x9 : ffff8000100ca6b0
>>>    x8 : 000000000017ffe8 x7 : c0000000fffeffff x6 : 0000000000000001
>>>    x5 : ffff800011d8c000 x4 : ffff800011d8c740 x3 : 0000000000000000
>>>    x2 : ffff0001108301c0 x1 : ab3c90eedf9c0f00 x0 : 0000000000000000
>>>    Call trace:
>>>     debug_print_object+0xb8/0x100
>>>     __debug_check_no_obj_freed+0x1c0/0x230
>>>     debug_check_no_obj_freed+0x20/0x88
>>>     slab_free_freelist_hook+0x154/0x1c8
>>>     kfree+0x114/0x5d0
>>>     sugov_exit+0xbc/0xc0
>>>     cpufreq_exit_governor+0x44/0x90
>>>     cpufreq_set_policy+0x268/0x4a8
>>>     store_scaling_governor+0xe0/0x128
>>>     store+0xc0/0xf0
>>>     sysfs_kf_write+0x54/0x80
>>>     kernfs_fop_write_iter+0x128/0x1c0
>>>     new_sync_write+0xf0/0x190
>>>     vfs_write+0x2d4/0x478
>>>     ksys_write+0x74/0x100
>>>     __arm64_sys_write+0x24/0x30
>>>     invoke_syscall.constprop.0+0x54/0xe0
>>>     do_el0_svc+0x64/0x158
>>>     el0_svc+0x2c/0xb0
>>>     el0t_64_sync_handler+0xb0/0xb8
>>>     el0t_64_sync+0x198/0x19c
>>>    irq event stamp: 5518
>>>    hardirqs last  enabled at (5517): [<ffff8000100cbd7c>] console_unlock+0x554/0x6c8
>>>    hardirqs last disabled at (5518): [<ffff800010fc0638>] el1_dbg+0x28/0xa0
>>>    softirqs last  enabled at (5504): [<ffff8000100106e0>] __do_softirq+0x4d0/0x6c0
>>>    softirqs last disabled at (5483): [<ffff800010049548>] irq_exit+0x1b0/0x1b8
>>>
>>> So split the original sugov_tunables_free() into two functions,
>>> sugov_clear_global_tunables() is just used to clear the global_tunables
>>> and the new sugov_tunables_free() is used as kobj_type::release to
>>> release the sugov_tunables safely.
>>>
>>> Fixes: 9bdcb44e391d ("cpufreq: schedutil: New governor based on scheduler utilization data")
>>> Cc: 4.7+ <stable@vger.kernel.org> # 4.7+
>>> Signed-off-by: Kevin Hao <haokexin@gmail.com>
>>> Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>> ---
>>>   kernel/sched/cpufreq_schedutil.c |   16 +++++++++++-----
>>>   1 file changed, 11 insertions(+), 5 deletions(-)
>>>
>>> --- a/kernel/sched/cpufreq_schedutil.c
>>> +++ b/kernel/sched/cpufreq_schedutil.c
>>> @@ -610,9 +610,17 @@ static struct attribute *sugov_attrs[] =
>>>   };
>>>   ATTRIBUTE_GROUPS(sugov);
>>> +static void sugov_tunables_free(struct kobject *kobj)
>>> +{
>>> +	struct gov_attr_set *attr_set = container_of(kobj, struct gov_attr_set, kobj);
>>> +
>>> +	kfree(to_sugov_tunables(attr_set));
>>> +}
>>> +
>>>   static struct kobj_type sugov_tunables_ktype = {
>>>   	.default_groups = sugov_groups,
>>>   	.sysfs_ops = &governor_sysfs_ops,
>>> +	.release = &sugov_tunables_free,
>>>   };
>>>   /********************** cpufreq governor interface *********************/
>>> @@ -712,12 +720,10 @@ static struct sugov_tunables *sugov_tuna
>>>   	return tunables;
>>>   }
>>> -static void sugov_tunables_free(struct sugov_tunables *tunables)
>>> +static void sugov_clear_global_tunables(void)
>>>   {
>>>   	if (!have_governor_per_policy())
>>>   		global_tunables = NULL;
>>> -
>>> -	kfree(tunables);
>>>   }
>>>   static int sugov_init(struct cpufreq_policy *policy)
>>> @@ -780,7 +786,7 @@ out:
>>>   fail:
>>>   	kobject_put(&tunables->attr_set.kobj);
>>>   	policy->governor_data = NULL;
>>> -	sugov_tunables_free(tunables);
>>> +	sugov_clear_global_tunables();
>>>   stop_kthread:
>>>   	sugov_kthread_stop(sg_policy);
>>> @@ -807,7 +813,7 @@ static void sugov_exit(struct cpufreq_po
>>>   	count = gov_attr_set_put(&tunables->attr_set, &sg_policy->tunables_hook);
>>>   	policy->governor_data = NULL;
>>>   	if (!count)
>>> -		sugov_tunables_free(tunables);
>>> +		sugov_clear_global_tunables();
>>>   	mutex_unlock(&global_tunables_lock);
>>>
>>>
>> Please defer this one.
>>
>> It uncovers a bug in cpufreq that needs to be fixed separately.
> 
> Now dropped from all queues, thanks!
> 
> greg k-h
> 

Hi Greg,

I am trying to get familiar with stable release process, because we
would like to start testing stable release candidates. But I cannot get
all the nuances how to get automatically information regarding rc code
ready to be tested.

Also I wonder how we could automatically detect situations when stable
release is expected to became diverged from the rc, e.g. like
[PATCH 5.10 033/306] cpufreq: schedutil: Use kobject release() method to
free sugov_tunables
was dropped from 5.10.67 without announcing the 5.10.67-rc2?

Any suggestions are appreciated.

Best regards,
Alexey Khoroshilov,
Linux Verification Center, ISPRAS