linux-phytec-fsl

ACPICA: Update use of acpi_os_wait_events_complete interface.

This patch cleans up all of the acpi_os_wait_events_complete() invocations to
make it to be invoked inside of ACPICA in the way to accommodate Linux's
work queue implementation.

According to the report, current Linux kernel code is facing a boot time
race issue in the acpi_remove_notify_handler(). This is because:
Linux is using work queues to implement a deferred handler call environment
while ACPICA expects OSPM to implement acpi_os_wait_events_complete() using
wait queues.  The position to invoke a "waiter" is not suitable for a
"flusher" as new invocations can be scheduled after this position and
before the deletion of the handler from its management container.

Since the following commit has deleted acpi_os_wait_events_complete()
parameters, it thus might not be possible for OSPM to achieve a safe
removal using wait queues.  This requires ACPICA to be changed accordingly
to "flush" handlers rather than "wait" them to be drain up:

  Commit: 5ff986a2a9db11858247b71fe242fe17617229aa
  Date: Wed, 16 May 2012 13:36:07 -0700
  Subject: Introduce acpi_os_wait_events_complete interface.

  This interface will block until asynchronous events like notifies
  and GPEs are complete. Within ACPICA, it is called before a notify or GPE
  handler is removed. ACPICA BZ 868.

This patch fixes this issue by invoking acpi_os_wait_events_complete() in the
way to "flush" things - it thus should be put to the position after handler
is removed from its management container but before it is destructed.

The technical concerns are:
1. MTX_NAMESPACE is used to protect things that acpi_os_wait_events_complete()
   might be waiting for, thus MTX_NAMESPACE must be unlocked before
   invoking acpi_os_wait_events_complete().
2. MTX_NAMESPACE is also used to implement the serialization of
   acpi_install_notify_handler() and acpi_remove_notify_handler(). This patch
   changes this logic, thus if there are many
   acpi_install/remove_notify_handler() invoked in parallel, the
   acpi_os_wait_events_complete() might face the races which could cause it
   never running to an end.  Normally this will require additional code to
   implement a separate locking facility which is not implemented due to 3.
3. Given ACPICA users will always invoke acpi_install_notify_handler() once
   during Linux module/device initialization and invoke
   acpi_remove_notify_handler() once during module/device finalization,
   problem stated in 2 will not happen in Linux environment due to the
   mutual exclusive module/device existence, this fix thus is sufficient.
Same concerns can apply to acpi_install/remove_gpe_handler(). Reported and
tested: Ronald Vink.  Fixed: Lv Zheng.

References: https://bugzilla.kernel.org/show_bug.cgi?id=60583
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Reported-and-Tested-by: Ronald Vink <ronald.vink@boskalis.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>