oom: make oom_reaper freezable
authorMichal Hocko <mhocko@suse.com>
Fri, 25 Mar 2016 21:20:41 +0000 (14:20 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Fri, 25 Mar 2016 23:37:42 +0000 (16:37 -0700)
After "oom: clear TIF_MEMDIE after oom_reaper managed to unmap the
address space" oom_reaper will call exit_oom_victim on the target task
after it is done.  This might however race with the PM freezer:

CPU0 CPU1 CPU2
freeze_processes
  try_to_freeze_tasks
   # Allocation request
out_of_memory
  oom_killer_disable
  wake_oom_reaper(P1)
   __oom_reap_task
  exit_oom_victim(P1)
    wait_event(oom_victims==0)
[...]
     do_exit(P1)
  perform IO/interfere with the freezer

which breaks the oom_killer_disable semantic.  We no longer have a
guarantee that the oom victim won't interfere with the freezer because
it might be anywhere on the way to do_exit while the freezer thinks the
task has already terminated.  It might trigger IO or touch devices which
are frozen already.

In order to close this race, make the oom_reaper thread freezable.  This
will work because
a) already running oom_reaper will block freezer to enter the
   quiescent state
b) wake_oom_reaper will not wake up the reaper after it has been
   frozen
c) the only way to call exit_oom_victim after try_to_freeze_tasks
   is from the oom victim's context when we know the further
   interference shouldn't be possible

Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: David Rientjes <rientjes@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/oom_kill.c

index a49638f..8cc55f0 100644 (file)
@@ -525,6 +525,8 @@ static void oom_reap_task(struct task_struct *tsk)
 
 static int oom_reaper(void *unused)
 {
+       set_freezable();
+
        while (true) {
                struct task_struct *tsk = NULL;