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Subject: Re: [PATCH 5.13 039/380] cpufreq: schedutil: Use kobject release()
 method to free sugov_tunables
To:     Sasha Levin <sashal@kernel.org>
CC:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        <linux-kernel@vger.kernel.org>, <stable@vger.kernel.org>,
        Kevin Hao <haokexin@gmail.com>,
        Viresh Kumar <viresh.kumar@linaro.org>
References: <20210916155803.966362085@linuxfoundation.org>
 <20210916155805.299153663@linuxfoundation.org>
 <6592ddb7-3705-6eab-f54c-3f12dbd58a44@intel.com> <YUPB2HlDaoLfNrQ2@sashalap>
From:   "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Organization: Intel Technology Poland Sp. z o. o., KRS 101882, ul. Slowackiego
 173, 80-298 Gdansk
Message-ID: <f23cfecb-acb4-6026-f4a7-36971e2c3faf@intel.com>
Date:   Fri, 1 Oct 2021 19:10:54 +0200
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On 9/17/2021 12:14 AM, Sasha Levin wrote:
> On Thu, Sep 16, 2021 at 06:55:49PM +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
>>> @@ -536,9 +536,17 @@ 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 
>>> *********************/
>>> @@ -638,12 +646,10 @@ 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)
>>> @@ -706,7 +712,7 @@ 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);
>>> @@ -733,7 +739,7 @@ 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 adding this one.
>
> I'll drop, let us know when to bring it back.
>
You've just picked up the commit that this one depends on ("cpufreq: 
schedutil: Destroy mutex before kobject_put() frees the memory".