PCI/ASPM: Handle PCI-to-PCIe bridges as roots of PCIe hierarchies

In a struct pcie_link_state, link->root points to the pcie_link_state of
the root of the PCIe hierarchy.  For the topmost link, this points to
itself (link->root = link).  For others, we copy the pointer from the
parent (link->root = link->parent->root).

Previously we recognized that Root Ports originated PCIe hierarchies, but
we treated PCI/PCI-X to PCIe Bridges as being in the middle of the
hierarchy, and when we tried to copy the pointer from link->parent->root,
there was no parent, and we dereferenced a NULL pointer:

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000090
  IP: [<ffffffff9e424350>] pcie_aspm_init_link_state+0x170/0x820

Recognize that PCI/PCI-X to PCIe Bridges originate PCIe hierarchies just
like Root Ports do, so link->root for these devices should also point to
itself.

Fixes: 51ebfc92b72b ("PCI: Enumerate switches below PCI-to-PCIe bridges")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=193411
Link: https://bugzilla.opensuse.org/show_bug.cgi?id=1022181
Tested-by: lists@ssl-mail.com
Tested-by: Jayachandran C. <jnair@caviumnetworks.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: stable@vger.kernel.org	# v4.2+

path: root/net/6lowpan/nhc_routing.c

/*
 *	6LoWPAN IPv6 Routing Header compression according to RFC6282
 *
 *	This program is free software; you can redistribute it and/or
 *	modify it under the terms of the GNU General Public License
 *	as published by the Free Software Foundation; either version
 *	2 of the License, or (at your option) any later version.
 */

#include "nhc.h"

#define LOWPAN_NHC_ROUTING_IDLEN	1
#define LOWPAN_NHC_ROUTING_ID_0		0xe2
#define LOWPAN_NHC_ROUTING_MASK_0	0xfe

static void routing_nhid_setup(struct lowpan_nhc *nhc)
{
	nhc->id[0] = LOWPAN_NHC_ROUTING_ID_0;
	nhc->idmask[0] = LOWPAN_NHC_ROUTING_MASK_0;
}

LOWPAN_NHC(nhc_routing, "RFC6282 Routing", NEXTHDR_ROUTING, 0,
	   routing_nhid_setup, LOWPAN_NHC_ROUTING_IDLEN, NULL, NULL);

module_lowpan_nhc(nhc_routing);
MODULE_DESCRIPTION("6LoWPAN next header RFC6282 Routing compression");
MODULE_LICENSE("GPL");