linux-kernel - Re: [PATCHv3 3/4] drivers/base: clean up the usage of devices_kset_move

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Message-ID: <2842715.a5PfnD4e6X@aspire.rjw.lan>
Date:   Wed, 04 Jul 2018 12:17:06 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Pingfan Liu <kernelfans@...il.com>
Cc:     Grygorii Strashko <grygorii.strashko@...com>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Dave Young <dyoung@...hat.com>, linux-pci@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCHv3 3/4] drivers/base: clean up the usage of devices_kset_move_last()

On Wednesday, July 4, 2018 6:40:09 AM CEST Pingfan Liu wrote:
> On Tue, Jul 3, 2018 at 10:28 PM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> >
> > On Tuesday, July 3, 2018 8:50:41 AM CEST Pingfan Liu wrote:
> > > 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@...uxfoundation.org>
> > > Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > Cc: Grygorii Strashko <grygorii.strashko@...com>
> > > Cc: Christoph Hellwig <hch@...radead.org>
> > > Cc: Bjorn Helgaas <helgaas@...nel.org>
> > > Cc: Dave Young <dyoung@...hat.com>
> > > Cc: linux-pci@...r.kernel.org
> > > Cc: linuxppc-dev@...ts.ozlabs.org
> > > Signed-off-by: Pingfan Liu <kernelfans@...il.com>
> > > ---
> > >  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.

> 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

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

Thanks,
Rafael