[PATCH] Fix NULL ptr dereference in pci_bus_assign_domain_nr() on ARM

On Mon, Mar 07, 2016 at 10:24:27PM -0600, Bjorn Helgaas wrote:

[...]

quoted

quoted

Actually, I did find one problem report:
http://forum.doozan.com/read.php?2,17868,22070,quote=1 from last May,
but apparently it got lost in a forum and never found its way
upstream.

I reworked the changelog because this problem will affect *any* arch
that enables CONFIG_PCI_DOMAINS_GENERIC and supplies NULL "parent"
pointers -- ia64, mips, mn10300, s390, x86, etc., would be affected if
they enabled CONFIG_PCI_DOMAINS_GENERIC.

I also added a "Fixes:" tag for 7c674700098c, since that's the commit
that added the generic code we're fixing.  Backports of 7c674700098c
should also backport this change.

That's really unfortunate, when I moved code from arm64 to generic I
did not spot this issue in the original code and carried it over, you
summarized the reasons in the commit log so without any further ado (and
with my apologies):

Acked-by: Lorenzo Pieralisi <redacted>

No worries, it just goes with the territory.  What surprises me is
that it took us so long to notice.  v4.0 was released almost a year
ago (April 12, 2015), so I can't figure out how nobody noticed until
now.

And I don't know what happened with the problem report in the forum.
That's a case where somebody *did* notice, but I guess they just gave
up on v4.0 and went back to v3.18.  What a shame :)  I don't know if
people just have low expectations of Linux, or they feel like it's too
hard to report bugs, or we don't make it easy enough, or we're not
approachable enough, or what.  I notice that many times somebody finds
a workaround, and people seem satisfied with that, and we don't get a
chance to fix the real problem.

I agree it is a pity the problem was not reported upstream which would
have solved the issue (that I should have spotted anyway while moving
the code) a long time ago, unfortunately I think it has to do with
how often developers/distros upgrade their kernels on these boards/socs
and how they interact with upstream, which is a discussion worth having.

Thank you !
Lorenzo