If an SR-IOV enabled device is held by vfio, and the device is removed, vfio will hold device lock and notify userspace of the removal. If userspace reads the sriov_numvfs sysfs entry, that thread will be blocked since sriov_numvfs_show() also tries to acquire the device lock. If that same thread is responsible for releasing the device to vfio, it results in a deadlock.
The proper way to detect a change to the num_VFs value is to listen for a sysfs event, not to add a device_lock() on the attribute _show() in the kernel. This reverts commit 35ff867b76576e32f34c698ccd11343f7d616204. Revert had a small conflict, the sprintf() is now changed to sysfs_emit(). Link: https://lore.kernel.org/linux-pci/ZXJI5+f8bUelVXqu@ubuntu/ Suggested-by: Leon Romanovsky <[email protected]> Reviewed-by: Leon Romanovsky <[email protected]> Signed-off-by: Jim Harris <[email protected]> --- drivers/pci/iov.c | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-) diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c index aaa33e8dc4c9..0ca20cd518d5 100644 --- a/drivers/pci/iov.c +++ b/drivers/pci/iov.c @@ -395,14 +395,8 @@ static ssize_t sriov_numvfs_show(struct device *dev, char *buf) { struct pci_dev *pdev = to_pci_dev(dev); - u16 num_vfs; - - /* Serialize vs sriov_numvfs_store() so readers see valid num_VFs */ - device_lock(&pdev->dev); - num_vfs = pdev->sriov->num_VFs; - device_unlock(&pdev->dev); - return sysfs_emit(buf, "%u\n", num_vfs); + return sysfs_emit(buf, "%u\n", pdev->sriov->num_VFs); } /*
