Re: [PATCH] driver core: Drop devices_kset_move_last() call from really_probe()

[Bjorn Helgaas <bhelgaas@google.com>]

On Fri, Jul 6, 2018 at 5:01 AM Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> The devices_kset_move_last() call in really_probe() is a mistake
> as it may cause parents to follow children in the devices_kset list
> which then causes system shutdown to fail.  Namely, if a device has
> children before really_probe() is called for it (which is not
> uncommon), that call will cause it to be reordered after the children
> in the devices_kset list and the ordering of that list will not
> reflect the correct device shutdown order.
>
> Also it causes the devices_kset list to be constantly reordered
> until all drivers have been probed which is totally pointless
> overhead in the majority of cases.
>
> For that reason, revert the really_probe() modifications made by
> commit 52cdbdd49853.

I'm sure you've considered this, but I can't figure out whether this
patch will reintroduce the problem that was solved by 52cdbdd49853.
That patch updated two places: (1) really_probe(), the change you're
reverting here, and (2) device_move().

device_move() is only called from 4-5 places, none of which look
related to the problem fixed by 52cdbdd49853, so it seems like that
problem was probably resolved by the hunk you're reverting.

> Fixes: 52cdbdd49853 (driver core: correct device's shutdown order)
> Link: https://lore.kernel.org/lkml/CAFgQCTt7VfqM=UyCnvNFxrSw8Z6cUtAi3HUwR4_xPAc03SgHjQ@mail.gmail.com/
> Reported-by: Pingfan Liu <kernelfans@gmail.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>  drivers/base/dd.c |    8 --------
>  1 file changed, 8 deletions(-)
>
> Index: linux-pm/drivers/base/dd.c
> ===================================================================
> --- linux-pm.orig/drivers/base/dd.c
> +++ linux-pm/drivers/base/dd.c
> @@ -434,14 +434,6 @@ re_probe:
>                         goto probe_failed;
>         }
>
> -       /*
> -        * Ensure devices are listed in devices_kset in correct order
> -        * It's important to move Dev to the end of devices_kset before
> -        * calling .probe, because it could be recursive and parent Dev
> -        * should always go first
> -        */
> -       devices_kset_move_last(dev);
> -
>         if (dev->bus->probe) {
>                 ret = dev->bus->probe(dev);
>                 if (ret)
>