[PATCH 3/5 V2] PCI/ERR: get device before call device driver to avoid NULL pointer reference

[Ethan Zhao <haifeng.zhao@intel.com>]

During DPC error injection test we found there is race condition between
pciehp and DPC driver, NULL pointer reference caused panic as following

 # setpci -s 64:02.0 0x196.w=000a
  // 64:02.0 is rootport has DPC capability
 # setpci -s 65:00.0 0x04.w=0544
  // 65:00.0 is NVMe SSD populated in above port
 # mount /dev/nvme0n1p1 nvme

 (tested on stable 5.8 & ICS(Ice Lake SP platform, see
 https://en.wikichip.org/wiki/intel/microarchitectures/ice_lake_(server))

 Buffer I/O error on dev nvme0n1p1, logical block 468843328,
 async page read
 BUG: kernel NULL pointer dereference, address: 0000000000000050
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 0
 Oops: 0000 [#1] SMP NOPTI
 CPU: 12 PID: 513 Comm: irq/124-pcie-dp Not tainted 5.8.0-0.0.7.el8.x86_64+ #1
 RIP: 0010:report_error_detected.cold.4+0x7d/0xe6
 Code: b6 d0 e8 e8 fe 11 00 e8 16 c5 fb ff be 06 00 00 00 48 89 df e8 d3 65 ff
 ff b8 06 00 00 00 e9 75 fc ff ff 48 8b 43 68 45 31 c9 <48> 8b 50 50 48 83 3a 00
 41 0f 94 c1 45 31 c0 48 85 d2 41 0f 94 c0
 RSP: 0018:ff8e06cf8762fda8 EFLAGS: 00010246
 RAX: 0000000000000000 RBX: ff4e3eaacf42a000 RCX: ff4e3eb31f223c01
 RDX: ff4e3eaacf42a140 RSI: ff4e3eb31f223c00 RDI: ff4e3eaacf42a138
 RBP: ff8e06cf8762fdd0 R08: 00000000000000bf R09: 0000000000000000
 R10: 000000eb8ebeab53 R11: ffffffff93453258 R12: 0000000000000002
 R13: ff4e3eaacf42a130 R14: ff8e06cf8762fe2c R15: ff4e3eab44733828
 FS:  0000000000000000(0000) GS:ff4e3eab1fd00000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000000050 CR3: 0000000f8f80a004 CR4: 0000000000761ee0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 PKRU: 55555554
 Call Trace:
 ? report_normal_detected+0x20/0x20
 report_frozen_detected+0x16/0x20
 pci_walk_bus+0x75/0x90
 ? dpc_irq+0x90/0x90
 pcie_do_recovery+0x157/0x201
 ? irq_finalize_oneshot.part.47+0xe0/0xe0
 dpc_handler+0x29/0x40
 irq_thread_fn+0x24/0x60
 irq_thread+0xea/0x170
 ? irq_forced_thread_fn+0x80/0x80
 ? irq_thread_check_affinity+0xf0/0xf0
 kthread+0x124/0x140
 ? kthread_park+0x90/0x90
 ret_from_fork+0x1f/0x30
 Modules linked in: nft_fib_inet.........
 CR2: 0000000000000050

Though we partly close the race condition with patch 'PCI: pciehp: check
and wait port status out of DPC before handling DLLSC and PDC', but there
is no hardware spec or software sequence to guarantee the pcie_ist() run
into pci_wait_port_outdpc() first or DPC triggered status bits being set
first when errors triggered DPC containment procedure, so device still
could be removed by function pci_stop_and_removed_bus_device() then freed
by pci_dev_put() in pciehp driver first during pcie_do_recover()/
pci_walk_bus() is called by dpc_handler() in DPC driver.

Maybe unify pci_bus_sem and pci_rescan_remove_lock to serialize the
removal and walking operation is the right way, but here we use
pci_dev_get() to increase the reference count of device before using the
device to avoid it is freed in use.

With this patch and patch 'PCI: pciehp: check and wait port status out of
DPC before handling DLLSC and PDC', stable 5.9-rc6 could pass the error
injection test and no panic happened.

Brute DPC error injection script:

for i in {0..100}
do
        setpci -s 64:02.0 0x196.w=000a
        setpci -s 65:00.0 0x04.w=0544
        mount /dev/nvme0n1p1 /root/nvme
        sleep 1
done

Signed-off-by: Ethan Zhao <haifeng.zhao@intel.com>
Tested-by: Wen Jin <wen.jin@intel.com>
Tested-by: Shanshan Zhang <ShanshanX.Zhang@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
Changes:
 V2: revise doc according to Andy's suggestion.

 drivers/pci/pcie/err.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
index c543f419d8f9..e35c4480c86b 100644
--- a/drivers/pci/pcie/err.c
+++ b/drivers/pci/pcie/err.c
@@ -52,6 +52,8 @@ static int report_error_detected(struct pci_dev *dev,
 	pci_ers_result_t vote;
 	const struct pci_error_handlers *err_handler;
 
+	if (!pci_dev_get(dev))
+		return 0;
 	device_lock(&dev->dev);
 	if (!pci_dev_set_io_state(dev, state) ||
 		!dev->driver ||
@@ -76,6 +78,7 @@ static int report_error_detected(struct pci_dev *dev,
 	pci_uevent_ers(dev, vote);
 	*result = merge_result(*result, vote);
 	device_unlock(&dev->dev);
+	pci_dev_put(dev);
 	return 0;
 }
 
@@ -94,6 +97,8 @@ static int report_mmio_enabled(struct pci_dev *dev, void *data)
 	pci_ers_result_t vote, *result = data;
 	const struct pci_error_handlers *err_handler;
 
+	if (!pci_dev_get(dev))
+		return 0;
 	device_lock(&dev->dev);
 	if (!dev->driver ||
 		!dev->driver->err_handler ||
@@ -105,6 +110,7 @@ static int report_mmio_enabled(struct pci_dev *dev, void *data)
 	*result = merge_result(*result, vote);
 out:
 	device_unlock(&dev->dev);
+	pci_dev_put(dev);
 	return 0;
 }
 
@@ -113,6 +119,8 @@ static int report_slot_reset(struct pci_dev *dev, void *data)
 	pci_ers_result_t vote, *result = data;
 	const struct pci_error_handlers *err_handler;
 
+	if (!pci_dev_get(dev))
+		return 0;
 	device_lock(&dev->dev);
 	if (!dev->driver ||
 		!dev->driver->err_handler ||
@@ -124,6 +132,7 @@ static int report_slot_reset(struct pci_dev *dev, void *data)
 	*result = merge_result(*result, vote);
 out:
 	device_unlock(&dev->dev);
+	pci_dev_put(dev);
 	return 0;
 }
 
@@ -131,6 +140,8 @@ static int report_resume(struct pci_dev *dev, void *data)
 {
 	const struct pci_error_handlers *err_handler;
 
+	if (!pci_dev_get(dev))
+		return 0;
 	device_lock(&dev->dev);
 	if (!pci_dev_set_io_state(dev, pci_channel_io_normal) ||
 		!dev->driver ||
@@ -143,6 +154,7 @@ static int report_resume(struct pci_dev *dev, void *data)
 out:
 	pci_uevent_ers(dev, PCI_ERS_RESULT_RECOVERED);
 	device_unlock(&dev->dev);
+	pci_dev_put(dev);
 	return 0;
 }
 
-- 
2.18.4