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

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Message-ID: <20180626115402.GB30256@kroah.com>
Date:   Tue, 26 Jun 2018 19:54:02 +0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Pingfan Liu <kernelfans@...il.com>
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
Subject: Re: [PATCHv2 2/2] drivers/base: reorder consumer and its children
 behind suppliers

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.

thanks,

greg k-h