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

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Date:   Tue, 10 Jul 2018 17:47:15 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     "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>,
        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 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.

thanks,

greg k-h