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

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Date:   Wed, 11 Jul 2018 00:43:55 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.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>
Subject: Re: [PATCH v2] driver core: Partially revert "driver core: correct
 device's shutdown order"

Hi,

On Tuesday 10 July 2018 09:17 PM, Greg Kroah-Hartman wrote:
> On Tue, Jul 10, 2018 at 05:40:21PM +0200, Rafael J. Wysocki wrote:
>> 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. :-)
> 
> Being bug compatible is key :)
> 
> I'll add a stable tag.

sure. If I see the issue in dra7, I'll send a stable fix in omap_hsmmmc driver.

Thanks
Kishon