• Tejun Heo's avatar
    freezer: make freezing() test freeze conditions in effect instead of TIF_FREEZE · a3201227
    Tejun Heo authored
    Using TIF_FREEZE for freezing worked when there was only single
    freezing condition (the PM one); however, now there is also the
    cgroup_freezer and single bit flag is getting clumsy.
    thaw_processes() is already testing whether cgroup freezing in in
    effect to avoid thawing tasks which were frozen by both PM and cgroup
    freezers.
    
    This is racy (nothing prevents race against cgroup freezing) and
    fragile.  A much simpler way is to test actual freeze conditions from
    freezing() - ie. directly test whether PM or cgroup freezing is in
    effect.
    
    This patch adds variables to indicate whether and what type of
    freezing conditions are in effect and reimplements freezing() such
    that it directly tests whether any of the two freezing conditions is
    active and the task should freeze.  On fast path, freezing() is still
    very cheap - it only tests system_freezing_cnt.
    
    This makes the clumsy dancing aroung TIF_FREEZE unnecessary and
    freeze/thaw operations more usual - updating state variables for the
    new state and nudging target tasks so that they notice the new state
    and comply.  As long as the nudging happens after state update, it's
    race-free.
    
    * This allows use of freezing() in freeze_task().  Replace the open
      coded tests with freezing().
    
    * p != current test is added to warning printing conditions in
      try_to_freeze_tasks() failure path.  This is necessary as freezing()
      is now true for the task which initiated freezing too.
    
    -v2: Oleg pointed out that re-freezing FROZEN cgroup could increment
         system_freezing_cnt.  Fixed.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Acked-by: Paul Menage <paul@paulmenage.org>  (for the cgroup portions)
    a3201227
freezer.h 5.44 KB