linux-kernel - Re: [PATCH 02/13] leds: el15203000: Fix devm vs. non-devm ordering

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Message-ID: <d509ee79-e73a-b236-bed9-8d40b8f6d460@huaweicloud.com>
Date:   Tue, 15 Nov 2022 10:06:22 +0800
From:   Wei Yongjun <weiyongjun@...weicloud.com>
To:     Oleh Kravchenko <oleg@....org.ua>, wangyufen <wangyufen@...wei.com>
Cc:     linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org,
        Pavel Machek <pavel@....cz>
Subject: Re: [PATCH 02/13] leds: el15203000: Fix devm vs. non-devm ordering

Hi Oleh,

On 2022/11/11 18:39, Oleh Kravchenko wrote:
> Hello Wang,
> 
>> 11 лист. 2022 р. о 11:21 wangyufen <wangyufen@...wei.com> написав(ла):
>>
>>
>> 在 2022/11/9 18:43, Oleh Kravchenko 写道:
>>>
>>>
>>>> 9 лист. 2022 р. о 12:25 wangyufen <wangyufen@...wei.com> написав(ла):
>>>>
>>>>
>>>> 在 2022/11/9 17:39, Oleh Kravchenko 写道:
>>>>
>>>>>> -static void el15203000_remove(struct spi_device *spi)
>>>>>>
>>>>> Is remove() callback from struct spi_driver deprecated?
>>>>>
>>>> It is not that remove() callback is deprecated,
>>>> it's that after wrapping mutex_destroy() call with devm_add_action_or_reset(),
>>>> remove() callback is unnecessary here.
>>>>
>>> When remove() is called, the memory allocated by devm_*() is valid.
>>> So what you try to fix here?
>>
>> Fix the &priv->lock used after destroy, for details, please see patch #0
>> LKML: Wang Yufen: [PATCH 00/13] leds: Fix devm vs. non-devm ordering
> 
> It doesn’t make any sense for me.
> You saying that remove() called before devm_* allocation
> if it true then set_brightness_delayed() will crash the system in anyway.
> 
> LED device has a parent SPI device; LED device can’t exist without SPI device.
> 
> So deallocation order should be next:
> 1. LED device devm_*()
> 2. SPI device remove()

The allocation order is as follows:

el15203000_probe()
  mutex_init(&priv->lock);
  el15203000_probe_dt(priv)
    device_for_each_child_node(priv->dev, child) {
      ...
      led->ldev.brightness_set_blocking = el15203000_set_blocking;
      ...
      devm_led_classdev_register_ext(priv->dev, &led->ldev, &init_data);
         dr = devres_alloc(devm_led_classdev_release, sizeof(*dr), GFP_KERNEL);
         <-- dr->node.release = devm_led_classdev_release()
         ...
         devres_add(parent, dr);
         <-- add dr->node to &priv->dev->devres_head

And the full deallocation order should be this:

1. SPI device .remove callback
2. LED device devm_*()
3. SPI device deallocation

spi_unregister_device()
  device_del()
    bus_remove_device()
      device_release_driver_internal()
        __device_release_driver()
          ...
	  device_remove()
	    spi_remove()   <-- call el15203000_remove() here, mutex_destroy(&priv->lock), lock destroy
          ...
          device_unbind_cleanup()
            devres_release_all()
              release_nodes()
              <-- traverse spi->dev->devres_head list and call dr->node.release in sequence.
                   devm_led_classdev_release()
                     led_classdev_unregister()
                     <-- flush set_brightness_work here, before the work flush, set_brightness_work may be sched.
                     <-- that is el15203000_set_blocking()..-> mutex_lock(&led->priv->lock) is called,
                     <-- this leads to the priv->lock use after destroy.
 put_device(&spi->dev) <-- spi device is deallocation in here


Regards,
Wei Yongjun