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SubjectRe: [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@linuxfoundation.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@linuxfoundation.org>
> > > Cc: Grygorii Strashko <grygorii.strashko@ti.com>
> > > Cc: Christoph Hellwig <hch@infradead.org>
> > > Cc: Bjorn Helgaas <helgaas@kernel.org>
> > > Cc: Dave Young <dyoung@redhat.com>
> > > Cc: linux-pci@vger.kernel.org
> > > Cc: linuxppc-dev@lists.ozlabs.org
> > > Signed-off-by: Pingfan Liu <kernelfans@gmail.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

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