Re: [PATCHv3 3/4] drivers/base: clean up the usage of devices_kset_move_last()

On Wed, Jul 4, 2018 at 6:18 PM Rafael J. Wysocki [off-list ref] wrote:

On Wednesday, July 4, 2018 6:40:09 AM CEST Pingfan Liu wrote:

quoted

On Tue, Jul 3, 2018 at 10:28 PM Rafael J. Wysocki [off-list ref] wrote:

quoted

On Tuesday, July 3, 2018 8:50:41 AM CEST Pingfan Liu wrote:

quoted

Clean up the referring to the code in commit 52cdbdd49853 ("driver core:
correct device's shutdown order"). So later we can revert it safely.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Rafael J. Wysocki <redacted>
Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Bjorn Helgaas <helgaas@kernel.org>
Cc: Dave Young <redacted>
Cc: linux-pci@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Pingfan Liu <redacted>
---
 drivers/base/core.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 684b994..db3deb8 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c

@@ -127,13 +127,6 @@ static int device_reorder_to_tail(struct device *dev, void *not_used)
 {
      struct device_link *link;

-     /*
-      * Devices that have not been registered yet will be put to the ends
-      * of the lists during the registration, so skip them here.
-      */
-     if (device_is_registered(dev))
-             devices_kset_move_last(dev);
-
      if (device_pm_initialized(dev))
              device_pm_move_last(dev);

You can't do this.

If you do it, that will break power management in some situations.

Could you shed light on it? I had a quick browsing of pm code, but it
is a big function, and I got lost in it.
If the above code causes failure, then does it imply that the seq in
devices_kset should be the same as dpm_list?

Generally, yes it should.

quoted

But in device_shutdown(), it only intersect with pm by
pm_runtime_get_noresume(dev) and pm_runtime_barrier(dev). How do these
function affect the seq in dpm_list?

They are not related to dpm_list directly.

However, if you shut down a supplier device before its consumer and that
involves power management, then the consumer shutdown may fail and lock up
the system

Ah, get your point. The patch in this series "[PATCHv3 2/4]
drivers/base: utilize device tree info to shutdown devices" still obey
the shutdown order "parent<-child" and "supplier<-consumer". It just
utilizes device-tree info to achieve this, since it turns out not easy
to maintain such order in devices_kset. As I described in the commit
log of [2/4], it needs two nested recursion, and should consider the
breakage of devices_kset's spinlock.

I asked you elsewhere to clearly describe the problem you are trying to
address.  Please do that in the first place.

OK, I will reply your question in [0/4]

Thanks,
Pingfan