• Mauricio Faria de Oliveira's avatar
    powerpc/pseries: use pci_host_bridge.release_fn() to kfree(phb) · 2dd9c11b
    Mauricio Faria de Oliveira authored
    This patch leverages 'struct pci_host_bridge' from the PCI subsystem
    in order to free the pci_controller only after the last reference to
    its devices is dropped (avoiding an oops in pcibios_release_device()
    if the last reference is dropped after pcibios_free_controller()).
    
    The patch relies on pci_host_bridge.release_fn() (and .release_data),
    which is called automatically by the PCI subsystem when the root bus
    is released (i.e., the last reference is dropped).  Those fields are
    set via pci_set_host_bridge_release() (e.g. in the platform-specific
    implementation of pcibios_root_bridge_prepare()).
    
    It introduces the 'pcibios_free_controller_deferred()' .release_fn()
    and it expects .release_data to hold a pointer to the pci_controller.
    
    The function implictly calls 'pcibios_free_controller()', so an user
    must *NOT* explicitly call it if using the new _deferred() callback.
    
    The functionality is enabled for pseries (although it isn't platform
    specific, and may be used by cxl).
    
    Details on not-so-elegant design choices:
    
     - Use 'pci_host_bridge.release_data' field as pointer to associated
       'struct pci_controller' so *not* to 'pci_bus_to_host(bridge->bus)'
       in pcibios_free_controller_deferred().
    
       That's because pci_remove_root_bus() sets 'host_bridge->bus = NULL'
       (so, if the last reference is released after pci_remove_root_bus()
       runs, which eventually reaches pcibios_free_controller_deferred(),
       that would hit a null pointer dereference).
    
       The cxl/vphb.c code calls pci_remove_root_bus(), and the cxl folks
       are interested in this fix.
    
    Test-case #1 (hold references)
    
      # ls -ld /sys/block/sd* | grep -m1 0021:01:00.0
      <...> /sys/block/sdaa -> ../devices/pci0021:01/0021:01:00.0/<...>
    
      # ls -ld /sys/block/sd* | grep -m1 0021:01:00.1
      <...> /sys/block/sdab -> ../devices/pci0021:01/0021:01:00.1/<...>
    
      # cat >/dev/sdaa & pid1=$!
      # cat >/dev/sdab & pid2=$!
    
      # drmgr -w 5 -d 1 -c phb -s 'PHB 33' -r
      Validating PHB DLPAR capability...yes.
      [  594.306719] pci_hp_remove_devices: PCI: Removing devices on bus 0021:01
      [  594.306738] pci_hp_remove_devices:    Removing 0021:01:00.0...
      ...
      [  598.236381] pci_hp_remove_devices:    Removing 0021:01:00.1...
      ...
      [  611.972077] pci_bus 0021:01: busn_res: [bus 01-ff] is released
      [  611.972140] rpadlpar_io: slot PHB 33 removed
    
      # kill -9 $pid1
      # kill -9 $pid2
      [  632.918088] pcibios_free_controller_deferred: domain 33, dynamic 1
    
    Test-case #2 (don't hold references)
    
      # drmgr -w 5 -d 1 -c phb -s 'PHB 33' -r
      Validating PHB DLPAR capability...yes.
      [  916.357363] pci_hp_remove_devices: PCI: Removing devices on bus 0021:01
      [  916.357386] pci_hp_remove_devices:    Removing 0021:01:00.0...
      ...
      [  920.566527] pci_hp_remove_devices:    Removing 0021:01:00.1...
      ...
      [  933.955873] pci_bus 0021:01: busn_res: [bus 01-ff] is released
      [  933.955977] pcibios_free_controller_deferred: domain 33, dynamic 1
      [  933.955999] rpadlpar_io: slot PHB 33 removed
    Suggested-By: default avatarGavin Shan <gwshan@linux.vnet.ibm.com>
    Signed-off-by: default avatarMauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
    Reviewed-by: default avatarGavin Shan <gwshan@linux.vnet.ibm.com>
    Reviewed-by: default avatarAndrew Donnellan <andrew.donnellan@au1.ibm.com>
    Tested-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com> # cxl
    Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
    2dd9c11b
pci.c 4.39 KB