linux-kernel - Re: [PATCH] driver core: Move device_links_purge() after bus_remove

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Date:   Thu, 19 Oct 2017 01:36:27 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Jeffy Chen <jeffy.chen@...k-chips.com>
Cc:     linux-kernel@...r.kernel.org, seanpaul@...omium.irg,
        briannorris@...omium.org, heiko@...ech.de,
        gregkh@...uxfoundation.org, dmitry.torokhov@...il.com,
        dianders@...omium.org, tfiga@...omium.org, broonie@...nel.org,
        thierry.reding@...il.com
Subject: Re: [PATCH] driver core: Move device_links_purge() after bus_remove_device()

On Wednesday, October 18, 2017 1:28:38 PM CEST Jeffy Chen wrote:
> Currently we are unbinding device link consumers when detaching the
> supplier. So we need to make sure the detaching happens before purging
> the supplier's device links.
> 
> Move device_links_purge() after bus_remove_device() in device_del()
> for that.
> 
> Signed-off-by: Jeffy Chen <jeffy.chen@...k-chips.com>

Yes, we can do that, but the changelog is somewhat hard to understand IMO.

Why don't you write something like the following:

"The current ordering of code in device_del() triggers a WARN_ON()
in device_links_purge(), because of an unexpected link status.

The device_links_unbind_consumers() call in device_release_driver()
has to take place before device_links_purge() for the status of all
links to be correct, so move the device_links_purge() call in
device_del() after the invocation of bus_remove_device() which calls
device_release_driver()."

> ---
> 
>  drivers/base/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 12ebd055724c..2e683cdf4a08 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -1958,7 +1958,6 @@ void device_del(struct device *dev)
>  		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
>  					     BUS_NOTIFY_DEL_DEVICE, dev);
>  
> -	device_links_purge(dev);
>  	dpm_sysfs_remove(dev);
>  	if (parent)
>  		klist_del(&dev->p->knode_parent);
> @@ -1986,6 +1985,7 @@ void device_del(struct device *dev)
>  	device_pm_remove(dev);
>  	driver_deferred_probe_del(dev);
>  	device_remove_properties(dev);
> +	device_links_purge(dev);
>  
>  	/* Notify the platform of the removal, in case they
>  	 * need to do anything...
>