linux-kernel - Re: [PATCH v2] driver core: Partially revert "driver core: correct device's shutdown order"

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Message-ID: <CAJZ5v0iV0ZaCbhoVOrGx08f6Y7Ei2q+qazxEMQRYD4LAq9LUbA@mail.gmail.com>
Date:   Tue, 10 Jul 2018 17:40:21 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        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>,
        Kishon Vijay Abraham I <kishon@...com>
Subject: Re: [PATCH v2] driver core: Partially revert "driver core: correct
 device's shutdown order"

On Tue, Jul 10, 2018 at 2:59 PM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Tue, Jul 10, 2018 at 02:51:33PM +0200, 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 covered an issue
>> with system shutdown, while system-wide suspend/resume potentially
>> had the same issue on the affected platforms (which was not covered).
>>
>> Moreover, the shutdown issue originally addressed by the change in
>> really_probe() made by commit 52cdbdd49853 is not present in 4.18-rc
>> any more, since dra7 started to use the sdhci-omap driver which
>> doesn't disable any regulators during shutdown, so the really_probe()
>> part of commit 52cdbdd49853 can be safely reverted.  [The original
>> issue was related to the omap_hsmmc driver used by dra7 previously.]
>>
>> For the above reasons, revert the really_probe() modifications made
>> by commit 52cdbdd49853.
>>
>> 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>
>> Reviewed-by: Kishon Vijay Abraham I <kishon@...com>
>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>> ---
>>
>> -> v2: Added information from Kishon on the fact that it should be safe
>>        to revert the really_probe() modifications added by the
>>        problematic commit.  Also added the Reviewed-by tag from Kishon.
>
> Looks good to me, want me to queue it up in my tree, or are you going to
> send it on to Linus?

Please queue it up.

> And shouldn't this have a stable tag as well?

That is sort of a gray area, because I think it may expose the
shutdown issue on dra7 in -stable, but technically it still fixes a
regression in the driver core.  So your call I suppose. :-)

FWIW, commit 52cdbdd49853 went in during the 4.3 cycle AFAICS.

Cheers,
Rafael