[PATCH] freezer: Get out of refrigerator if fatal signals arepending

[Michal Hocko]

We should make sure that the current task doesn't enter refrigerator if
it has fatal signals pending because it should get to the signals
processing as soon as possible.

This closes a possible race when OOM killer selects a task which is
about to enter the fridge but it is not set as frozen yet. This will
lead to a livelock because select_bad_process would skip that task due
to TIF_MEMDIE set for the process but there is no chance for further
process.
oom_kill_task                           refrigerator
  set_tsk_thread_flag(p, TIF_MEMDIE);
  force_sig(SIGKILL, p);
  if (frozen(p))
        thaw_process(p)
                                          frozen_process();
                                          [...]
                                          if (!frozen(current))
                                                break;
                                          schedule();

select_bad_process
  [...]
  if (test_tsk_thread_flag(p, TIF_MEMDIE))
          return ERR_PTR(-1UL);

Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
---
 kernel/freezer.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/kernel/freezer.c b/kernel/freezer.c
index 7b01de9..74b8434 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -48,6 +48,10 @@ void refrigerator(void)
 	current->flags |= PF_FREEZING;
 
 	for (;;) {
+		if (fatal_signal_pending(current)) {
+			current->flags &= ~PF_FROZEN;
+			break;
+		}
 		set_current_state(TASK_UNINTERRUPTIBLE);
 		if (!frozen(current))
 			break;
-- 
1.7.6.3

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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