linux-kernel - Re: [PATCHv2 2/2] drivers/base: reorder consumer and its children behind suppliers

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Message-ID: <CAFgQCTuztrZbFJF3_NgZrq2r0ngSmcnkXMB=CgvMNgzQkwe+4w@mail.gmail.com>
Date:   Tue, 3 Jul 2018 14:48:00 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     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@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, rafael.j.wysocki@...el.com
Subject: Re: [PATCHv2 2/2] drivers/base: reorder consumer and its children
 behind suppliers

On Tue, Jun 26, 2018 at 7:54 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Tue, Jun 26, 2018 at 11:29:48AM +0800, Pingfan Liu wrote:
> > On Mon, Jun 25, 2018 at 6:45 PM Greg Kroah-Hartman
> > <gregkh@...uxfoundation.org> wrote:
> > >
> > > On Mon, Jun 25, 2018 at 03:47:39PM +0800, Pingfan Liu wrote:
> > > > commit 52cdbdd49853 ("driver core: correct device's shutdown order")
> > > > introduces supplier<-consumer order in devices_kset. The commit tries
> > > > to cleverly maintain both parent<-child and supplier<-consumer order by
> > > > reordering a device when probing. This method makes things simple and
> > > > clean, but unfortunately, breaks parent<-child order in some case,
> > > > which is described in next patch in this series.
> > >
> > > There is no "next patch in this series" :(
> > >
> > Oh, re-arrange the patches, and forget the comment in log
> >
> > > > Here this patch tries to resolve supplier<-consumer by only reordering a
> > > > device when it has suppliers, and takes care of the following scenario:
> > > >     [consumer, children] [ ... potential ... ] supplier
> > > >                          ^                   ^
> > > > After moving the consumer and its children after the supplier, the
> > > > potentail section may contain consumers whose supplier is inside
> > > > children, and this poses the requirement to dry out all consumpers in
> > > > the section recursively.
> > > >
> > > > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > > 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>
> > > > ---
> > > > note: there is lock issue in this patch, should be fixed in next version
> > >
> > > Please send patches that you know are correct, why would I want to
> > > review this if you know it is not correct?
> > >
> > > And if the original commit is causing problems for you, why not just
> > > revert that instead of adding this much-increased complexity?
> > >
> > Revert the original commit, then it will expose the error  order
> > "consumer <- supplier" again.
> > This patch tries to resolve the error and fix the following scenario:
> > step0:  before the consumer device's probing,  (note child_a is a
> > supplier of consumer_a, etc)
> > [ consumer-X,  child_a, ...., child_z]     [.... consumer_a, ...,
> > consumer_z, ....]    supplier-X
> >                                                              ^^^
> > affected range during moving^^^
> > step1: When probing, moving consumer-X after supplier-X
> > [ child_a, ...., child_z]     [.... consumer_a, ...,     consumer_z,
> > ....]   supplier-X, consumer-X
> > But it breaks "parent <-child" seq now, and should be fixed like:
> > step2:
> > [.... consumer_a, ...,     consumer_z, ....]  supplier-X  [
> > consumer-X,  child_a, ...., child_z]    <---
> > descendants_reorder_after_pos() does it.
> > Again, the seq "consumer_a <- child_a" breaks the "supplier<-consumer"
> >  order, should be fixed like:
> > step3:
> > [....  consumer_z, .....]  supplier-X  [ consumer-X,  child_a,
> > consumer_a ...., child_z]   <--- __device_reorder_consumer() does it.
> > ^^ affected range^^
> > The moving of consumer_a brings us to face the same scenario of step1,
> > hence we need an external recursion.
>
> Something really got messed up here, and this all does not make any
> sense :(
>
> Can you try again?
>
> Also, please cc: Rafael on all of this, as he wrote all of this
> consumer/supplier logic and I am not that familiar with it at all.
>
Cc Rafael J. Wysocki for the context.  I will send out V3 soon.

Regards,
Pingfan