From: Wen Congyang <wencongya...@huawei.com>
Hi, Alex Williamson
When using vfio, we encounter a problem: too many lspci processes are blocked
in D state.
I analyzed all processes, and found one process is blocked in pci_dev_lock(),
another
process is blocked in vfio_del_group_put(). I checked the backtrace, and found
the following
race condition:
Process A(use sysfs to unbind the device):
device_release_driver()
device_lock(dev)
__device_release_driver()
dev->bus->remove(dev) // pci_device_remove()
drv->remove(pci_dev) // vfio_pci_remove()
vfio_del_group_dev()
vfio_device_put()
wait vfio_device is remove from the group. Process B gets
vfio_device,
so we will wait it.
Process B:
vfio_group_fops_unl_ioctl()
vfio_group_get_device_fd()
vfio_device_get_from_name() // we get vfio_device here
device->ops->open() // vfio_pci_open()
vfio_pci_enable()
pci_reset_function()
pci_dev_reset(dev, 0)
pci_dev_lock()
pci_cfg_access_lock(dev) // After this, lspci will
be blocked
device_lock(&dev->dev) // the lock is hold by
another process A
Now, Process A is waiting Process B, and Process B is waiting Process A.
I think we use pci_try_reset_function() to instead of pci_reset_function() can
break this deadwait.
Thanks,
Wen Congyang
