linux-kernel - Re: [PATCH] driver core: Make sure device detached from driver before deleting it

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Date:   Wed, 18 Oct 2017 19:11:04 +0800
From:   jeffy <jeffy.chen@...k-chips.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
CC:     linux-kernel@...r.kernel.org, dmitry.torokhov@...il.com,
        heiko@...ech.de, briannorris@...omium.org, dianders@...omium.org,
        tfiga@...omium.org, broonie@...nel.org, seanpaul@...omium.org,
        thierry.reding@...il.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] driver core: Make sure device detached from driver before
 deleting it

Hi Rafael,

Thanks for your reply.

On 10/18/2017 06:04 PM, Rafael J. Wysocki wrote:
> But device_del() calls bus_remove_device() which in turn calls
> device_release_driver(), so this looks like an ordering issue to me.
>
uh, right, didn't notice that, it indeed to be a ordering issue...

it turns out in device_del() we are calling device_links_purge() before 
bus_remove_device()...

> What*exactly*  is not working?  Or rather, what symptoms do you see?
>
my board has these devices:
spi master device->spi child device->spi based pwm->pwm_bl

and i add a device link to the pwm and pwm_bl, and got a warning about 
the pwm not unbound:

static void device_links_purge(struct device *dev)
{
...
         list_for_each_entry_safe_reverse(link, ln, 
&dev->links.consumers, s_node) {
                 WARN_ON(link->status != DL_STATE_DORMANT &&
                         link->status != DL_STATE_NONE); <-- warning here!
                 __device_link_del(link);
         }


and i was confused by:
static void mac80211_hwsim_del_radio(struct mac80211_hwsim_data *data,
                                      const char *hwname,
                                      struct genl_info *info)
{
...
         device_release_driver(data->dev);
         device_unregister(data->dev);

and adding that device_release_driver hide that issue(oops...)


so we should move device_links_purge() after bus_remove_device() in 
device_del() right? maybe after device_remove_properties(), and that did 
solve the issue :)


> Thanks,
> Rafael