PCI: Protect pci_bus->slots with pci_slot_mutex, not pci_bus_sem

Rajat Jain reported a deadlock when PCIe hot-add and AER recovery happen at
the same time:

thread 1:

  pciehp_enable_slot
    pciehp_configure_device
      pci_bus_add_devices
        pci_bus_add_device
          device_attach
            device_lock(dev)                       # acquire device lock
            ...
            pciehp_probe
              init_slot
                pci_hp_register
                  pci_create_slot
                    down_write(pci_bus_sem)        # deadlock here

thread 2:

  aer_isr_one_error
    aer_process_err_device
      do_recovery
        broadcast_error_message(..., report_error_detected)
          pci_walk_bus(..., cb=report_error_detected, ...)
            down_read(&pci_bus_sem)                # acquire pci_bus_sem
            report_error_detected(dev)             # cb()
              device_lock(dev)                     # deadlock here

Previously, the bus->devices and bus->slots list were protected by
pci_bus_sem.  In pci_create_slot(), we held it for writing so we could
add to the bus->slots list.

Add a new local pci_slot_mutex to protect bus->slots.  Hold pci_bus_sem for
reading while searching the bus->devices list.

[bhelgaas: changelog]
Link: http://lkml.kernel.org/r/CAA93t1qpPqbih+UB0McA_d_+2rVaNkXsinAUxYzK9+JXSS+L-g@mail.gmail.com
Reported-by: Rajat Jain <rajatja@google.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/linux/pci.h b/include/linux/pci.h
index 8a0321a8fb59..aaee493174e2 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -446,7 +446,8 @@ struct pci_bus {
         struct list_head children;      /* list of child buses */
         struct list_head devices;       /* list of devices on this bus */
         struct pci_dev  *self;          /* bridge device as seen by parent */
-        struct list_head slots;         /* list of slots on this bus */
+        struct list_head slots;         /* list of slots on this bus;
+                                           protected by pci_slot_mutex */
         struct resource *resource[PCI_BRIDGE_RESOURCE_NUM];
         struct list_head resources;     /* address space routed to this bus */
         struct resource busn_res;       /* bus numbers routed to this bus */