[PATCH v3] PCI: Fix dropping valid root bus resources with .end = zero

[Geert Uytterhoeven <geert+renesas@glider.be>]

On r8a7791/koelsch:

    kmemleak: 1 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
    # cat /sys/kernel/debug/kmemleak
    unreferenced object 0xc3a34e00 (size 64):
      comm "swapper/0", pid 1, jiffies 4294937460 (age 199.080s)
      hex dump (first 32 bytes):
	b4 5d 81 f0 b4 5d 81 f0 c0 b0 a2 c3 00 00 00 00  .]...]..........
	00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
      backtrace:
	[<fe3aa979>] __kmalloc+0xf0/0x140
	[<34bd6bc0>] resource_list_create_entry+0x18/0x38
	[<767046bc>] pci_add_resource_offset+0x20/0x68
	[<b3f3edf2>] devm_of_pci_get_host_bridge_resources.constprop.0+0xb0/0x390

When coalescing two resources for a contiguous aperture, the second
resource is enlarged to cover the full contiguous range, while the
first resource is marked invalid.  This invalidation is done by
clearing the flags, start, and end members.

When adding the initial resources to the bus later, invalid resources
are skipped.  Unfortunately, the check for an invalid resource considers
only the end member, causing false positives.

E.g. on r8a7791/koelsch, root bus resource 0 ("bus 00") is skipped, and
no longer registered with pci_bus_insert_busn_res() (causing the memory
leak), nor printed:

     pci-rcar-gen2 ee090000.pci: host bridge /soc/pci@ee090000 ranges:
     pci-rcar-gen2 ee090000.pci:      MEM 0x00ee080000..0x00ee08ffff -> 0x00ee080000
     pci-rcar-gen2 ee090000.pci: PCI: revision 11
     pci-rcar-gen2 ee090000.pci: PCI host bridge to bus 0000:00
    -pci_bus 0000:00: root bus resource [bus 00]
     pci_bus 0000:00: root bus resource [mem 0xee080000-0xee08ffff]

Fix this by only skipping resources where all of the flags, start, and
end members are zero.

Fixes: 7c3855c423b17f6c ("PCI: Coalesce host bridge contiguous apertures")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>
Acked-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
---
Is there any side effect of not registering the root bus resource with
pci_bus_insert_busn_res()?  This is the resource created by
of_pci_parse_bus_range(), and thus affects any DT platforms using
"bus-range = <0 0>".

Perhaps checking for "!res->flags" would be sufficient?

I wonder if this still causes memory leaks on systems where resources
are coalesced, as the first resource of a contiguous aperture is no
longer referenced? Perhaps instead of clearing the resource, it should
be removed from the list (and freed? is it actually safe to do that?)?
  - Bjorn thinks these would normally be freed via
    __acpi_pci_root_release_info() (if the host bridge were
    hot-removed), so probably not a leak since the invalidated resource
    is still in the info->resources list and should be freed even though
    it's been invalidated.
  - Furthermore, Bjorn suspects it could probably be removed from the
    list and freed here, and maybe even in the first loop when we
    coalesce it, so we wouldn't have to check in the second loop.

However, let's fix one bug at a time? This has been dragging on for
about half a year....

Apparently Johannes had identified the bug before, but didn't realize
the full impact...
https://lore.kernel.org/r/5331e942ff28bb191d62bb403b03ceb7d750856c.camel@sipsolutions.net/

v3:
  - Actually the second resource is enlarged, and the first one is
    invalidated,

v2:
  - Add Tested-by, Acked-by.
---
 drivers/pci/probe.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 1779582fb5007cd1..5988584825482e9f 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -996,7 +996,7 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 	resource_list_for_each_entry_safe(window, n, &resources) {
 		offset = window->offset;
 		res = window->res;
-		if (!res->end)
+		if (!res->flags && !res->start && !res->end)
 			continue;
 
 		list_move_tail(&window->node, &bridge->windows);
-- 
2.34.1