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From:   "Rafael J. Wysocki" <rjw@rjwysocki.net>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Pingfan Liu <kernelfans@gmail.com>, linux-kernel@vger.kernel.org,
        Grygorii Strashko <grygorii.strashko@ti.com>,
        Christoph Hellwig <hch@infradead.org>,
        Bjorn Helgaas <helgaas@kernel.org>,
        Dave Young <dyoung@redhat.com>, linux-pci@vger.kernel.org,
        Lukas Wunner <lukas@wunner.de>,
        Linux PM <linux-pm@vger.kernel.org>,
        Kishon Vijay Abraham I <kishon@ti.com>
Subject: [PATCH v2] driver core: Partially revert "driver core: correct device's shutdown order"
Date:   Tue, 10 Jul 2018 14:51:33 +0200
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From: Rafael J. Wysocki <rafael.j.wysocki@intel.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@gmail.com>
Tested-by: Pingfan Liu <kernelfans@gmail.com>
Reviewed-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.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.

---
 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)