• Michal Hocko's avatar
    OOM, PM: OOM killed task shouldn't escape PM suspend · 5695be14
    Michal Hocko authored
    PM freezer relies on having all tasks frozen by the time devices are
    getting frozen so that no task will touch them while they are getting
    frozen. But OOM killer is allowed to kill an already frozen task in
    order to handle OOM situtation. In order to protect from late wake ups
    OOM killer is disabled after all tasks are frozen. This, however, still
    keeps a window open when a killed task didn't manage to die by the time
    freeze_processes finishes.
    
    Reduce the race window by checking all tasks after OOM killer has been
    disabled. This is still not race free completely unfortunately because
    oom_killer_disable cannot stop an already ongoing OOM killer so a task
    might still wake up from the fridge and get killed without
    freeze_processes noticing. Full synchronization of OOM and freezer is,
    however, too heavy weight for this highly unlikely case.
    
    Introduce and check oom_kills counter which gets incremented early when
    the allocator enters __alloc_pages_may_oom path and only check all the
    tasks if the counter changes during the freezing attempt. The counter
    is updated so early to reduce the race window since allocator checked
    oom_killer_disabled which is set by PM-freezing code. A false positive
    will push the PM-freezer into a slow path but that is not a big deal.
    
    Changes since v1
    - push the re-check loop out of freeze_processes into
      check_frozen_processes and invert the condition to make the code more
      readable as per Rafael
    
    Fixes: f660daac (oom: thaw threads if oom killed thread is frozen before deferring)
    Cc: 3.2+ <stable@vger.kernel.org> # 3.2+
    Signed-off-by: default avatarMichal Hocko <mhocko@suse.cz>
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    5695be14
oom_kill.c 20 KB