[PATCH v2] powerpc/eeh: Fix race with driver un/bind

[Michael Neuling <mikey@neuling.org>]

The current EEH callbacks can race with a driver unbind. This
can result in a backtraces like this:

[    7.573055] EEH: Frozen PHB#0-PE#1fc detected
[    7.573063] EEH: PE location: S000009, PHB location: N/A
[    7.573069] CPU: 2 PID: 2312 Comm: kworker/u258:3 Not tainted 4.15.6-openpower1 #2
[    7.573078] Workqueue: nvme-wq nvme_reset_work [nvme]
[    7.573080] Call Trace:
[    7.573088] [c000000ff12a3a30] [c0000000005f5000] dump_stack+0x9c/0xd0
[    7.573093]  (unreliable)
[    7.573106] [c000000ff12a3a70] [c00000000002385c] eeh_dev_check_failure+0x420/0x470
[    7.573111] [c000000ff12a3b10] [c00000000002394c] eeh_check_failure+0xa0/0xa4
[    7.573115] [c000000ff12a3b50] [c0080000088c2ff0] nvme_reset_work+0x138/0x1414 [nvme]
[    7.573122] [c000000ff12a3cb0] [c000000000089c78] process_one_work+0x1ec/0x328
[    7.573132] [c000000ff12a3d40] [c00000000008a3b4] worker_thread+0x2e4/0x3a8
[    7.573140] [c000000ff12a3dc0] [c00000000008fed0] kthread+0x14c/0x154
[    7.573150] [c000000ff12a3e30] [c00000000000b594] ret_from_kernel_thread+0x5c/0xc8
[    7.573183] nvme nvme1: Removing after probe failure status: -19
<snip>
cpu 0x23: Vector: 300 (Data Access) at [c000000ff50f3800]
    pc: c0080000089a0eb0: nvme_error_detected+0x4c/0x90 [nvme]
    lr: c000000000026564: eeh_report_error+0xe0/0x110
    sp: c000000ff50f3a80
   msr: 9000000000009033
   dar: 400
 dsisr: 40000000
  current = 0xc000000ff507c000
  paca    = 0xc00000000fdc9d80   softe: 0        irq_happened: 0x01
    pid   = 782, comm = eehd
Linux version 4.15.6-openpower1 (smc@smc-desktop) (gcc version 6.4.0 (Buildroot 2017.11.2-00008-g4b6188e)) #2 SM                                             P Tue Feb 27 12:33:27 PST 2018
enter ? for help
[c000000ff50f3af0] c000000000026564 eeh_report_error+0xe0/0x110
[c000000ff50f3b30] c000000000025520 eeh_pe_dev_traverse+0xc0/0xdc
[c000000ff50f3bc0] c000000000026bd0 eeh_handle_normal_event+0x184/0x4c4
[c000000ff50f3c70] c000000000026ff4 eeh_handle_event+0x30/0x288
[c000000ff50f3d10] c00000000002758c eeh_event_handler+0x124/0x170
[c000000ff50f3dc0] c00000000008fed0 kthread+0x14c/0x154
[c000000ff50f3e30] c00000000000b594 ret_from_kernel_thread+0x5c/0xc8

The first part is an EEH (on boot), the second half is the resulting
crash. nvme probe starts the nvme_reset_work() worker thread. This
worker thread starts touching the device which see a device error
(EEH) and hence queues up an event in the powerpc EEH worker
thread. nvme_reset_work() then continues and runs
nvme_remove_dead_ctrl_work() which results in unbinding the driver
from the device and hence releases all resources. At the same time,
the EEH worker thread starts doing the EEH .error_detected() driver
callback, which no longer works since the resources have been freed.

This fixes the problem in the same way the generic PCIe AER code (in
drivers/pci/pcie/aer/aerdrv_core.c) does. It makes the EEH code hold
the device_lock() while performing the driver EEH callbacks and
associated code. This ensures either the callbacks are no longer
register, or if they are registered the driver will not be removed
from underneath us.

This has been broken forever. The EEH call backs were first introduced
in 2005 (in 77bd7415610) but it's not clear if a lock was needed back
then.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Cc: stable@vger.kernel.org
---
v2:
  Updates based on benh's comments:
  - Change jump labels
  - Clarify where lock is held in commit message
---
 arch/powerpc/kernel/eeh_driver.c | 68 +++++++++++++++++++++++++---------------
 1 file changed, 42 insertions(+), 26 deletions(-)

diff --git a/arch/powerpc/kernel/eeh_driver.c b/arch/powerpc/kernel/eeh_driver.c
index 0c0b66fc5b..295ba83384 100644
--- a/arch/powerpc/kernel/eeh_driver.c
+++ b/arch/powerpc/kernel/eeh_driver.c
@@ -207,18 +207,18 @@ static void *eeh_report_error(void *data, void *userdata)
 
 	if (!dev || eeh_dev_removed(edev) || eeh_pe_passed(edev->pe))
 		return NULL;
+
+	device_lock(&dev->dev);
 	dev->error_state = pci_channel_io_frozen;
 
 	driver = eeh_pcid_get(dev);
-	if (!driver) return NULL;
+	if (!driver) goto out_no_dev;
 
 	eeh_disable_irq(dev);
 
 	if (!driver->err_handler ||
-	    !driver->err_handler->error_detected) {
-		eeh_pcid_put(dev);
-		return NULL;
-	}
+	    !driver->err_handler->error_detected)
+		goto out;
 
 	rc = driver->err_handler->error_detected(dev, pci_channel_io_frozen);
 
@@ -227,8 +227,12 @@ static void *eeh_report_error(void *data, void *userdata)
 	if (*res == PCI_ERS_RESULT_NONE) *res = rc;
 
 	edev->in_error = true;
-	eeh_pcid_put(dev);
 	pci_uevent_ers(dev, PCI_ERS_RESULT_NONE);
+
+out:
+	eeh_pcid_put(dev);
+out_no_dev:
+	device_unlock(&dev->dev);
 	return NULL;
 }
 
@@ -251,15 +255,14 @@ static void *eeh_report_mmio_enabled(void *data, void *userdata)
 	if (!dev || eeh_dev_removed(edev) || eeh_pe_passed(edev->pe))
 		return NULL;
 
+	device_lock(&dev->dev);
 	driver = eeh_pcid_get(dev);
-	if (!driver) return NULL;
+	if (!driver) goto out_no_dev;
 
 	if (!driver->err_handler ||
 	    !driver->err_handler->mmio_enabled ||
-	    (edev->mode & EEH_DEV_NO_HANDLER)) {
-		eeh_pcid_put(dev);
-		return NULL;
-	}
+	    (edev->mode & EEH_DEV_NO_HANDLER))
+		goto out;
 
 	rc = driver->err_handler->mmio_enabled(dev);
 
@@ -267,7 +270,10 @@ static void *eeh_report_mmio_enabled(void *data, void *userdata)
 	if (rc == PCI_ERS_RESULT_NEED_RESET) *res = rc;
 	if (*res == PCI_ERS_RESULT_NONE) *res = rc;
 
+out:
 	eeh_pcid_put(dev);
+out_no_dev:
+	device_unlock(&dev->dev);
 	return NULL;
 }
 
@@ -290,20 +296,20 @@ static void *eeh_report_reset(void *data, void *userdata)
 
 	if (!dev || eeh_dev_removed(edev) || eeh_pe_passed(edev->pe))
 		return NULL;
+
+	device_lock(&dev->dev);
 	dev->error_state = pci_channel_io_normal;
 
 	driver = eeh_pcid_get(dev);
-	if (!driver) return NULL;
+	if (!driver) goto out_no_dev;
 
 	eeh_enable_irq(dev);
 
 	if (!driver->err_handler ||
 	    !driver->err_handler->slot_reset ||
 	    (edev->mode & EEH_DEV_NO_HANDLER) ||
-	    (!edev->in_error)) {
-		eeh_pcid_put(dev);
-		return NULL;
-	}
+	    (!edev->in_error))
+		goto out;
 
 	rc = driver->err_handler->slot_reset(dev);
 	if ((*res == PCI_ERS_RESULT_NONE) ||
@@ -311,7 +317,10 @@ static void *eeh_report_reset(void *data, void *userdata)
 	if (*res == PCI_ERS_RESULT_DISCONNECT &&
 	     rc == PCI_ERS_RESULT_NEED_RESET) *res = rc;
 
+out:
 	eeh_pcid_put(dev);
+out_no_dev:
+	device_unlock(&dev->dev);
 	return NULL;
 }
 
@@ -362,10 +371,12 @@ static void *eeh_report_resume(void *data, void *userdata)
 
 	if (!dev || eeh_dev_removed(edev) || eeh_pe_passed(edev->pe))
 		return NULL;
+
+	device_lock(&dev->dev);
 	dev->error_state = pci_channel_io_normal;
 
 	driver = eeh_pcid_get(dev);
-	if (!driver) return NULL;
+	if (!driver) goto out_no_dev;
 
 	was_in_error = edev->in_error;
 	edev->in_error = false;
@@ -375,18 +386,20 @@ static void *eeh_report_resume(void *data, void *userdata)
 	    !driver->err_handler->resume ||
 	    (edev->mode & EEH_DEV_NO_HANDLER) || !was_in_error) {
 		edev->mode &= ~EEH_DEV_NO_HANDLER;
-		eeh_pcid_put(dev);
-		return NULL;
+		goto out;
 	}
 
 	driver->err_handler->resume(dev);
 
-	eeh_pcid_put(dev);
 	pci_uevent_ers(dev, PCI_ERS_RESULT_RECOVERED);
+out:
+	eeh_pcid_put(dev);
 #ifdef CONFIG_PCI_IOV
 	if (eeh_ops->notify_resume && eeh_dev_to_pdn(edev))
 		eeh_ops->notify_resume(eeh_dev_to_pdn(edev));
 #endif
+out_no_dev:
+	device_unlock(&dev->dev);
 	return NULL;
 }
 
@@ -406,23 +419,26 @@ static void *eeh_report_failure(void *data, void *userdata)
 
 	if (!dev || eeh_dev_removed(edev) || eeh_pe_passed(edev->pe))
 		return NULL;
+
+	device_lock(&dev->dev);
 	dev->error_state = pci_channel_io_perm_failure;
 
 	driver = eeh_pcid_get(dev);
-	if (!driver) return NULL;
+	if (!driver) goto out_no_dev;
 
 	eeh_disable_irq(dev);
 
 	if (!driver->err_handler ||
-	    !driver->err_handler->error_detected) {
-		eeh_pcid_put(dev);
-		return NULL;
-	}
+	    !driver->err_handler->error_detected)
+		goto out;
 
 	driver->err_handler->error_detected(dev, pci_channel_io_perm_failure);
 
-	eeh_pcid_put(dev);
 	pci_uevent_ers(dev, PCI_ERS_RESULT_DISCONNECT);
+out:
+	eeh_pcid_put(dev);
+out_no_dev:
+	device_unlock(&dev->dev);
 	return NULL;
 }
 
-- 
2.14.1