• Rafael J. Wysocki's avatar
    ACPI / hotplug: Fix concurrency issues and memory leaks · 3757b948
    Rafael J. Wysocki authored
    This changeset is aimed at fixing a few different but related
    problems in the ACPI hotplug infrastructure.
    
    First of all, since notify handlers may be run in parallel with
    acpi_bus_scan(), acpi_bus_trim() and acpi_bus_hot_remove_device()
    and some of them are installed for ACPI handles that have no struct
    acpi_device objects attached (i.e. before those objects are created),
    those notify handlers have to take acpi_scan_lock to prevent races
    from taking place (e.g. a struct acpi_device is found to be present
    for the given ACPI handle, but right after that it is removed by
    acpi_bus_trim() running in parallel to the given notify handler).
    Moreover, since some of them call acpi_bus_scan() and
    acpi_bus_trim(), this leads to the conclusion that acpi_scan_lock
    should be acquired by the callers of these two funtions rather by
    these functions themselves.
    
    For these reasons, make all notify handlers that can handle device
    addition and eject events take acpi_scan_lock and remove the
    acpi_scan_lock locking from acpi_bus_scan() and acpi_bus_trim().
    Accordingly, update all of their users to make sure that they
    are always called under acpi_scan_lock.
    
    Furthermore, since eject operations are carried out asynchronously
    with respect to the notify events that trigger them, with the help
    of acpi_bus_hot_remove_device(), even if notify handlers take the
    ACPI scan lock, it still is possible that, for example,
    acpi_bus_trim() will run between acpi_bus_hot_remove_device() and
    the notify handler that scheduled its execution and that
    acpi_bus_trim() will remove the device node passed to
    acpi_bus_hot_remove_device() for ejection.  In that case, the struct
    acpi_device object obtained by acpi_bus_hot_remove_device() will be
    invalid and not-so-funny things will ensue.  To protect agaist that,
    make the users of acpi_bus_hot_remove_device() run get_device() on
    ACPI device node objects that are about to be passed to it and make
    acpi_bus_hot_remove_device() run put_device() on them and check if
    their ACPI handles are not NULL (make acpi_device_unregister() clear
    the device nodes' ACPI handles for that check to work).
    
    Finally, observe that acpi_os_hotplug_execute() actually can fail,
    in which case its caller ought to free memory allocated for the
    context object to prevent leaks from happening.  It also needs to
    run put_device() on the device node that it ran get_device() on
    previously in that case.  Modify the code accordingly.
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    Acked-by: default avatarYinghai Lu <yinghai@kernel.org>
    3757b948
dock.c 27.3 KB