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/include/net/netns/mib.h

#ifndef __NETNS_MIB_H__
#define __NETNS_MIB_H__

#include <net/snmp.h>

struct netns_mib {
	DEFINE_SNMP_STAT(struct tcp_mib, tcp_statistics);
	DEFINE_SNMP_STAT(struct ipstats_mib, ip_statistics);
	DEFINE_SNMP_STAT(struct linux_mib, net_statistics);
	DEFINE_SNMP_STAT(struct udp_mib, udp_statistics);
	DEFINE_SNMP_STAT(struct udp_mib, udplite_statistics);
	DEFINE_SNMP_STAT(struct icmp_mib, icmp_statistics);
	DEFINE_SNMP_STAT_ATOMIC(struct icmpmsg_mib, icmpmsg_statistics);

#if IS_ENABLED(CONFIG_IPV6)
	struct proc_dir_entry *proc_net_devsnmp6;
	DEFINE_SNMP_STAT(struct udp_mib, udp_stats_in6);
	DEFINE_SNMP_STAT(struct udp_mib, udplite_stats_in6);
	DEFINE_SNMP_STAT(struct ipstats_mib, ipv6_statistics);
	DEFINE_SNMP_STAT(struct icmpv6_mib, icmpv6_statistics);
	DEFINE_SNMP_STAT_ATOMIC(struct icmpv6msg_mib, icmpv6msg_statistics);
#endif
#ifdef CONFIG_XFRM_STATISTICS
	DEFINE_SNMP_STAT(struct linux_xfrm_mib, xfrm_statistics);
#endif
};

#endif