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

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Date:   Tue, 22 Nov 2022 09:10:12 +0800
From:   Wang Yufen <wangyufen@...weicloud.com>
To:     Wei Yongjun <weiyongjun@...weicloud.com>,
        Oleh Kravchenko <oleg@....org.ua>
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



在 2022/11/15 10:06, Wei Yongjun 写道:
> 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
> 
>
Hi Oleh,

Judging from the deallocation order above, there is a issue that the 
&priv->lock used after destroy, right?

And thanks Wei for the detailed explanation.

Thanks,
Wang


> Regards,
> Wei Yongjun
>