linux-kernel - Re: [PATCH] driver core: Partially revert "driver core: correct device's shutdown order"

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Date:   Tue, 10 Jul 2018 14:38:04 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Pingfan Liu <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>,
        Dave Young <dyoung@...hat.com>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Lukas Wunner <lukas@...ner.de>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] driver core: Partially revert "driver core: correct
 device's shutdown order"

Hi,

On Tue, Jul 10, 2018 at 2:22 PM, Kishon Vijay Abraham I <kishon@...com> wrote:
> Hi,
>
> On Tuesday 10 July 2018 05:05 PM, Rafael J. Wysocki wrote:
>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>
>> Commit 52cdbdd49853 (driver core: correct device's shutdown order)
>> introduced a regression by breaking device shutdown on some systems.
>>
>> Namely, the devices_kset_move_last() call in really_probe() added by
>> that commit is a mistake as it may cause parents to follow children
>> in the devices_kset list which then causes shutdown to fail.  For
>> example, 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 any more.
>>
>> 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 and it only covers an issue
>> with system shutdown, while system-wide suspend/resume potentially
>> has the same issue on the affected platforms (which is not covered).
>>
>> For that reason, revert the really_probe() modifications made by
>> commit 52cdbdd49853 which unfortunately will expose the shutdown
>> issue the problematic commit attempted to fix (and which will have
>> to be addressed differently and correctly in the future).
>>
>> The other code changes made by commit 52cdbdd49853 are useful and
>> they need not be reverted.
>>
>> 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>
>> Tested-by: Pingfan Liu <kernelfans@...il.com>
>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>> ---
>
> This issue because of which 52cdbdd49853 (driver core: correct device's
> shutdown order) was added is not present from 4.18, since dra7 started using
> sdhci-omap.c driver which doesn't disable regulator during shutdown. (The
> original issue was present in omap_hsmmc driver).
>
> When sdhci-omap driver is modified to disable regulator during shutdown,
> something like device_link_add() can be added in _regulator_get().
>
> Since this doesn't reintroduce the problem that was solved by 52cdbdd49853,
> this can be safely merged.

This is very useful information, let me add it to the patch changelog.

> Reviewed-by: Kishon Vijay Abraham I <kishon@...com>

Thank you!