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Subject[BUGFIX 1/2] PCI/PM: Fix deadlock when unbind device if its parent in D3cold
Date
If a PCI device and its parents are put into D3cold, unbinding the
device will trigger deadlock as follow:

- driver_unbind
- device_release_driver
- device_lock(dev) <--- previous lock here
- __device_release_driver
- pm_runtime_get_sync
...
- rpm_resume(dev)
- rpm_resume(dev->parent)
...
- pci_pm_runtime_resume
...
- pci_set_power_state
- __pci_start_power_transition
- pci_wakeup_bus(dev->parent->subordinate)
- pci_walk_bus
- device_lock(dev) <--- dead lock here


If we do not do device_lock in pci_walk_bus, we can avoid dead lock.
Device_lock in pci_walk_bus is introduced in commit:
d71374dafbba7ec3f67371d3b7e9f6310a588808, corresponding email thread
is: https://lkml.org/lkml/2006/5/26/38. The patch author Zhang Yanmin
said device_lock is added to pci_walk_bus because:

Some error handling functions call pci_walk_bus. For example, PCIe
aer. Here we lock the device, so the driver wouldn't detach from the
device, as the cb might call driver's callback function.

So I fixed the dead lock as follow:

- remove device_lock from pci_walk_bus
- add device_lock into callback if callback will call driver's callback

I checked pci_walk_bus users one by one, and found only PCIe aer needs
device lock.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Cc: Zhang Yanmin <yanmin.zhang@intel.com>
---
drivers/pci/bus.c | 3 ---
drivers/pci/pcie/aer/aerdrv_core.c | 20 ++++++++++++++++----
2 files changed, 16 insertions(+), 7 deletions(-)

--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -320,10 +320,7 @@ void pci_walk_bus(struct pci_bus *top, i
} else
next = dev->bus_list.next;

- /* Run device routines with the device locked */
- device_lock(&dev->dev);
retval = cb(dev, userdata);
- device_unlock(&dev->dev);
if (retval)
break;
}
--- a/drivers/pci/pcie/aer/aerdrv_core.c
+++ b/drivers/pci/pcie/aer/aerdrv_core.c
@@ -213,6 +213,7 @@ static int report_error_detected(struct
struct aer_broadcast_data *result_data;
result_data = (struct aer_broadcast_data *) data;

+ device_lock(&dev->dev);
dev->error_state = result_data->state;

if (!dev->driver ||
@@ -231,12 +232,14 @@ static int report_error_detected(struct
dev->driver ?
"no AER-aware driver" : "no driver");
}
- return 0;
+ goto out;
}

err_handler = dev->driver->err_handler;
vote = err_handler->error_detected(dev, result_data->state);
result_data->result = merge_result(result_data->result, vote);
+out:
+ device_unlock(&dev->dev);
return 0;
}

@@ -247,14 +250,17 @@ static int report_mmio_enabled(struct pc
struct aer_broadcast_data *result_data;
result_data = (struct aer_broadcast_data *) data;

+ device_lock(&dev->dev);
if (!dev->driver ||
!dev->driver->err_handler ||
!dev->driver->err_handler->mmio_enabled)
- return 0;
+ goto out;

err_handler = dev->driver->err_handler;
vote = err_handler->mmio_enabled(dev);
result_data->result = merge_result(result_data->result, vote);
+out:
+ device_unlock(&dev->dev);
return 0;
}

@@ -265,14 +271,17 @@ static int report_slot_reset(struct pci_
struct aer_broadcast_data *result_data;
result_data = (struct aer_broadcast_data *) data;

+ device_lock(&dev->dev);
if (!dev->driver ||
!dev->driver->err_handler ||
!dev->driver->err_handler->slot_reset)
- return 0;
+ goto out;

err_handler = dev->driver->err_handler;
vote = err_handler->slot_reset(dev);
result_data->result = merge_result(result_data->result, vote);
+out:
+ device_unlock(&dev->dev);
return 0;
}

@@ -280,15 +289,18 @@ static int report_resume(struct pci_dev
{
const struct pci_error_handlers *err_handler;

+ device_lock(&dev->dev);
dev->error_state = pci_channel_io_normal;

if (!dev->driver ||
!dev->driver->err_handler ||
!dev->driver->err_handler->resume)
- return 0;
+ goto out;

err_handler = dev->driver->err_handler;
err_handler->resume(dev);
+out:
+ device_unlock(&dev->dev);
return 0;
}


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