linux-kernel - Re: [PATCH] driver core: Drop devices_kset_move_last() call from really

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Date:   Mon, 9 Jul 2018 08:57:36 -0500
From:   Bjorn Helgaas <bhelgaas@...gle.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        kernelfans@...il.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Christoph Hellwig <hch@...radead.org>,
        Bjorn Helgaas <helgaas@...nel.org>, dyoung@...hat.com,
        linux-pci@...r.kernel.org, Lukas Wunner <lukas@...ner.de>,
        Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] driver core: Drop devices_kset_move_last() call from really_probe()

On Fri, Jul 6, 2018 at 5:01 AM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.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@...il.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.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)
>