Messages in this thread | | | Date | Thu, 28 Sep 2017 16:46:23 -0700 | From | Govindarajulu Varadarajan <> | Subject | Re: [PATCH 3/4] pci aer: fix deadlock in do_recovery |
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On Thu, 28 Sep 2017, Sinan Kaya wrote:
> On 9/27/2017 5:42 PM, Govindarajulu Varadarajan wrote: >> CPU0 CPU1 >> --------------------------------------------------------------------- >> __driver_attach() >> device_lock(&dev->mutex) <--- device mutex lock here >> driver_probe_device() >> pci_enable_sriov() >> pci_iov_add_virtfn() >> pci_device_add() >> aer_isr() <--- pci aer error >> do_recovery() >> broadcast_error_message() >> pci_walk_bus() >> down_read(&pci_bus_sem) <--- rd sem > > How about releasing the device_lock here on CPU0?>
pci_device_add() is called by driver's pci probe function. device_lock(dev) should be held before calling pci driver probe function.
> or in other words keep device_lock as short as possible?
The problem is not the duration device_lock is held. It is the order two locks are aquired. We cannot control or implement a restriction that during device_lock() is held, driver probe should not call pci function which aquires pci_bus_sem. And in case of pci aer, aer handler needs to call driver err_handler() for which we need to hold device_lock() before calling err_handler(). In order to find all the devices on a pci bus, we should hold pci_bus_sem to do pci_walk_bus().
>> down_write(&pci_bus_sem) <-- stuck on wr sem >> report_error_detected() >> device_lock(&dev->mutex)<--- DEAD LOCK
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