[PATCH 2/2] PCI: err: ensure stable topology during handling

[Keith Busch <kbusch@meta.com>]

From: Keith Busch <kbusch@kernel.org>

DPC and AER handling access their subordinate bus devices. If pciehp should
happen to also trigger during this handling, it will remove all the subordinate
buses, then dereferecing any children may be a use-after-free. That may lead to
kernel panics like the below.

 BUG: unable to handle page fault for address: 00000000091400c0
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 0 P4D 0
 Oops: 0000 [#1] SMP
 CPU: 15 PID: 2464 Comm: irq/53-pcie-dpc Kdump: loaded Tainted: G            E      6.9.0-0_fbk0_rc10_871_g4e98bf884071 #1
 RIP: 0010:pci_bus_read_config_dword+0x17/0x50
 Code: e9 0e 00 00 00 c7 01 ff ff ff ff b8 86 00 00 00 c3 cc cc 0f 1f 44 00 00 53 50 c7 44 24 04 00 00 00 00 f6 c2 03 75 27 48 89 cb <48> 8b 87 c0 00 00 00 4c 8d 44 24 04 b9 04 00 00 00 ff 50 18 85 c0
 RSP: 0018:ffffc90039113d60 EFLAGS: 00010246
 RAX: 0000000009140000 RBX: ffffc90039113d7c RCX: ffffc90039113d7c
 RDX: 0000000000000004 RSI: 0000000000000000 RDI: 0000000009140000
 RBP: 0000000000000100 R08: 0000000000000000 R09: 0000000000000001
 R10: 0000000000000000 R11: 0000001f975c6971 R12: 000000000000e9fc
 R13: ffff88811b5b4000 R14: ffffc90039113d7c R15: 0000000000000000
 FS:  0000000000000000(0000) GS:ffff899f7d3c0000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00000000091400c0 CR3: 00000243fb00f002 CR4: 0000000000770ef0
 PKRU: 55555554
 Call Trace:
  <TASK>
  ? __die+0x78/0xc0
  ? page_fault_oops+0x2a8/0x3a0
  ? sched_clock+0x5/0x10
  ? psi_task_switch+0x39/0xc90
  ? __switch_to+0x131/0x530
  ? exc_page_fault+0x63/0x130
  ? asm_exc_page_fault+0x22/0x30
  ? pci_bus_read_config_dword+0x17/0x50
  pci_dev_wait+0x107/0x190
  ? dpc_completed+0x50/0x50
  dpc_reset_link+0x4e/0xd0
  pcie_do_recovery+0xb2/0x2d0
  ? irq_forced_thread_fn+0x60/0x60
  dpc_handler+0x107/0x130
  irq_thread_fn+0x19/0x40
  irq_thread+0x120/0x1e0
  ? irq_thread_fn+0x40/0x40
  ? irq_forced_secondary_handler+0x20/0x20
  kthread+0xae/0xe0
  ? file_tty_write+0x360/0x360
  ret_from_fork+0x2f/0x40
  ? file_tty_write+0x360/0x360
  ret_from_fork_asm+0x11/0x20
  </TASK>

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 drivers/pci/pcie/err.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
index 31090770fffcc..5355fc0fbf910 100644
--- a/drivers/pci/pcie/err.c
+++ b/drivers/pci/pcie/err.c
@@ -192,7 +192,7 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
 		pci_channel_state_t state,
 		pci_ers_result_t (*reset_subordinates)(struct pci_dev *pdev))
 {
-	int type = pci_pcie_type(dev);
+	int type = pci_pcie_type(dev), ret;
 	struct pci_dev *bridge;
 	pci_ers_result_t status = PCI_ERS_RESULT_CAN_RECOVER;
 	struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
@@ -214,6 +214,10 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
 	else
 		bridge = pci_upstream_bridge(dev);
 
+
+	ret = pci_trylock_rescan_remove(bridge);
+	if (!ret)
+		return PCI_ERS_RESULT_DISCONNECT;
 	pci_walk_bridge(bridge, pci_pm_runtime_get_sync, NULL);
 
 	pci_dbg(bridge, "broadcast error_detected message\n");
@@ -262,12 +266,14 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
 	}
 
 	pci_walk_bridge(bridge, pci_pm_runtime_put, NULL);
+	pci_unlock_rescan_remove();
 
 	pci_info(bridge, "device recovery successful\n");
 	return status;
 
 failed:
 	pci_walk_bridge(bridge, pci_pm_runtime_put, NULL);
+	pci_unlock_rescan_remove();
 
 	pci_uevent_ers(bridge, PCI_ERS_RESULT_DISCONNECT);
 
-- 
2.43.0