From 61cf16d8bd38c3dc52033ea75d5b1f8368514a17 Mon Sep 17 00:00:00 2001 From: Alex Williamson Date: Mon, 16 Dec 2013 15:14:31 -0700 Subject: PCI: Add pci_try_reset_function(), pci_try_reset_slot(), pci_try_reset_bus() When doing a function/slot/bus reset PCI grabs the device_lock for each device to block things like suspend and driver probes, but call paths exist where this lock may already be held. This creates an opportunity for deadlock. For instance, vfio allows userspace to issue resets so long as it owns the device(s). If a driver unbind .remove callback races with userspace issuing a reset, we have a deadlock as userspace gets stuck waiting on device_lock while another thread has device_lock and waits for .remove to complete. To resolve this, we can make a version of the reset interfaces which use trylock. With this, we can safely attempt a reset and return error to userspace if there is contention. [bhelgaas: the deadlock happens when A (userspace) has a file descriptor for the device, and B waits in this path: driver_detach device_lock # take device_lock __device_release_driver pci_device_remove # pci_bus_type.remove vfio_pci_remove # pci_driver .remove vfio_del_group_dev wait_event(vfio.release_q, !vfio_dev_present) # wait (holding device_lock) Now B is stuck until A gives up the file descriptor. If A tries to acquire device_lock for any reason, we deadlock because A is waiting for B to release the lock, and B is waiting for A to release the file descriptor.] Signed-off-by: Alex Williamson Signed-off-by: Bjorn Helgaas --- include/linux/pci.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'include') diff --git a/include/linux/pci.h b/include/linux/pci.h index 9e3ec8b951b7..d21be0343865 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -948,10 +948,13 @@ int pcie_get_minimum_link(struct pci_dev *dev, enum pci_bus_speed *speed, int __pci_reset_function(struct pci_dev *dev); int __pci_reset_function_locked(struct pci_dev *dev); int pci_reset_function(struct pci_dev *dev); +int pci_try_reset_function(struct pci_dev *dev); int pci_probe_reset_slot(struct pci_slot *slot); int pci_reset_slot(struct pci_slot *slot); +int pci_try_reset_slot(struct pci_slot *slot); int pci_probe_reset_bus(struct pci_bus *bus); int pci_reset_bus(struct pci_bus *bus); +int pci_try_reset_bus(struct pci_bus *bus); void pci_reset_bridge_secondary_bus(struct pci_dev *dev); void pci_update_resource(struct pci_dev *dev, int resno); int __must_check pci_assign_resource(struct pci_dev *dev, int i); -- cgit v1.2.3