When we unbind vfio-pci from a device, while running a guest, we might
have a deadlock when such a guest reboots.
Unbind takes device_lock at device_release_driver, and waits for
release_q at vfio_del_group_dev.
release_q will only be woken up when all references to vfio_device are
gone, and that includes open file descriptors, like the ones a guest
on qemu will hold.
If you try to reboot the guest, it will call VFIO_DEVICE_RESET, which
calls pci_reset_function, which now grabs the device_lock, and we are
deadlocked.
Using device_trylock allow us to handle the case when the lock is
already taken, and avoid this situation.
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxxxxxxx>
---
Not tested yet, but I would like some comments now, like would it be
better to have a pci_try_reset_function, or do trylock on
pci_reset_function itself?
---
drivers/vfio/pci/vfio_pci.c | 14 ++++++++++++--
1 files changed, 12 insertions(+), 2 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 3b76dc8..d1d2242 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -513,8 +513,18 @@ static long vfio_pci_ioctl(void *device_data,
return ret;
} else if (cmd == VFIO_DEVICE_RESET) {
- return vdev->reset_works ?
- pci_reset_function(vdev->pdev) : -EINVAL;
+ struct pci_dev *pdev = vdev->pdev;
+ int ret = -EBUSY;
+ if (!vdev->reset_works)
+ return -EINVAL;
+ if (pci_cfg_access_trylock(pdev)) {
+ if (device_trylock(&pdev->dev)) {
+ ret = __pci_reset_function_locked(pdev);
+ device_unlock(&pdev->dev);
+ }
+ pci_cfg_access_unlock(pdev);
+ }
+ return ret;
} else if (cmd == VFIO_DEVICE_GET_PCI_HOT_RESET_INFO) {
struct vfio_pci_hot_reset_info hdr;
--
1.7.1
--
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