[PATCH v2 1/2] PCI: shpchp: Abort hot-plug if pci_hp_add_bridge() fails

[Nam Cao <namcao@linutronix.de>]

If a bridge is hot-added without any bus number available for its
downstream bus, pci_hp_add_bridge() will fail. However, the driver
proceeds regardless, and the kernel crashes.

This crash can be reproduced with the QEMU command:
    qemu-system-x86_64 -machine pc-q35-2.10 \
        -kernel bzImage \
        -drive "file=img,format=raw" \
        -m 2048 -smp 2 -enable-kvm \
        -append "console=ttyS0 root=/dev/sda" \
        -nographic \
        -device pcie-root-port,bus=pcie.0,id=rp1,slot=1,bus-reserve=0 \
        -device pcie-pci-bridge,id=br1,bus=rp1

then hot-plug a bridge at runtime with the QEMU command:
    device_add pci-bridge,id=br2,bus=br1,chassis_nr=1,addr=1

and the kernel crashes:

shpchp 0000:01:00.0: Latch close on Slot(1-1)
shpchp 0000:01:00.0: Button pressed on Slot(1-1)
shpchp 0000:01:00.0: Card present on Slot(1-1)
shpchp 0000:01:00.0: PCI slot #1-1 - powering on due to button press
pci 0000:02:01.0: [1b36:0001] type 01 class 0x060400 conventional PCI bridge
pci 0000:02:01.0: BAR 0 [mem 0x00000000-0x000000ff 64bit]
pci 0000:02:01.0: PCI bridge to [bus 00]
pci 0000:02:01.0:   bridge window [io  0x0000-0x0fff]
pci 0000:02:01.0:   bridge window [mem 0x00000000-0x000fffff]
pci 0000:02:01.0:   bridge window [mem 0x00000000-0x000fffff 64bit pref]
pci 0000:02:01.0: No bus number available for hot-added bridge

	(note: kernel should abort hot-plugging right here)

pci 0000:02:01.0: BAR 0 [mem 0xfe600000-0xfe6000ff 64bit]: assigned
shpchp 0000:01:00.0: PCI bridge to [bus 02]
shpchp 0000:01:00.0:   bridge window [io  0xc000-0xcfff]
shpchp 0000:01:00.0:   bridge window [mem 0xfe600000-0xfe7fffff]
shpchp 0000:01:00.0:   bridge window [mem 0xfe000000-0xfe1fffff 64bit pref]
shpchp 0000:02:01.0: HPC vendor_id 1b36 device_id 1 ss_vid 0 ss_did 0
shpchp 0000:02:01.0: enabling device (0000 -> 0002)
ACPI: \_SB_.GSIE: Enabled at IRQ 20
BUG: kernel NULL pointer dereference, address: 00000000000000da
PGD 0 P4D 0
Oops: 0002 [#1] PREEMPT SMP NOPTI
CPU: 1 PID: 66 Comm: kworker/1:2 Not tainted 6.9.0-rc1-00001-g2e0239d47d75 #33
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Workqueue: shpchp-1 shpchp_pushbutton_thread
RIP: 0010:shpc_init+0x3fb/0x9d0
[stack dump and register dump cut out]

Fix this by aborting the hot-plug if pci_hp_add_bridge() fails.

Fixes: 7d01f70ac6f4 ("PCI: shpchp: use generic pci_hp_add_bridge()")
Signed-off-by: Nam Cao <namcao@linutronix.de>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: <stable@vger.kernel.org>
---
v2:
  - add more information to commit description
  - return 0 instead of -EINVAL
  - remove pci_stop_and_remove_bus_device()

 drivers/pci/hotplug/shpchp_pci.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/hotplug/shpchp_pci.c b/drivers/pci/hotplug/shpchp_pci.c
index 36db0c3c4ea6..ca105aed7eee 100644
--- a/drivers/pci/hotplug/shpchp_pci.c
+++ b/drivers/pci/hotplug/shpchp_pci.c
@@ -48,8 +48,10 @@ int shpchp_configure_device(struct slot *p_slot)
 	}
 
 	for_each_pci_bridge(dev, parent) {
-		if (PCI_SLOT(dev->devfn) == p_slot->device)
-			pci_hp_add_bridge(dev);
+		if (PCI_SLOT(dev->devfn) == p_slot->device) {
+			if (pci_hp_add_bridge(dev))
+				goto out;
+		}
 	}
 
 	pci_assign_unassigned_bridge_resources(bridge);
-- 
2.39.2