[PATCH -v2] freezer: check OOM kill while being frozen

[Cong Wang]

Since f660daac474c6f (oom: thaw threads if oom killed thread is frozen
before deferring) OOM killer relies on being able to thaw a frozen task
to handle OOM situation but a3201227f803 (freezer: make freezing() test
freeze conditions in effect instead of TIF_FREEZE) has reorganized the
code and stopped clearing freeze flag in __thaw_task. This means that
the target task only wakes up and goes into the fridge again because the
freezing condition hasn't changed for it. This reintroduces the bug
fixed by f660daac474c6f.

Fix the issue by checking for TIF_MEMDIE thread flag and get away from
the fridge if it is set.

Changes since v1
- return __thaw_task into oom_scan_process_thread because
  oom_kill_process will not wake task in the fridge because it is
  sleeping uninterruptible

[mhocko@xxxxxxx: rewrote the changelog]
Fixes: a3201227f803 (freezer: make freezing() test freeze conditions in effect instead of TIF_FREEZE)
Cc: stable@xxxxxxxxxxxxxxx # 3.3+
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
---
 kernel/freezer.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/kernel/freezer.c b/kernel/freezer.c
index aa6a8aadb911..77ad6794b610 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -45,13 +45,28 @@ bool freezing_slow_path(struct task_struct *p)
 	if (pm_nosig_freezing || cgroup_freezing(p))
 		return true;
 
-	if (pm_freezing && !(p->flags & PF_KTHREAD))
+	if (!(p->flags & PF_KTHREAD))
 		return true;
 
 	return false;
 }
 EXPORT_SYMBOL(freezing_slow_path);
 
+static bool should_thaw_current(bool check_kthr_stop)
+{
+	if (!freezing(current))
+		return true;
+
+	if (check_kthr_stop && kthread_should_stop())
+		return true;
+
+	/* It might not be safe to check TIF_MEMDIE for pm freeze. */
+	if (cgroup_freezing(current) && test_thread_flag(TIF_MEMDIE))
+		return true;
+
+	return false;
+}
+
 /* Refrigerator is place where frozen processes are stored :-). */
 bool __refrigerator(bool check_kthr_stop)
 {
@@ -67,8 +82,7 @@ bool __refrigerator(bool check_kthr_stop)
 
 		spin_lock_irq(&freezer_lock);
 		current->flags |= PF_FROZEN;
-		if (!freezing(current) ||
-		    (check_kthr_stop && kthread_should_stop()))
+		if (should_thaw_current(check_kthr_stop))
 			current->flags &= ~PF_FROZEN;
 		spin_unlock_irq(&freezer_lock);
 
-- 
2.1.1

-- 
Michal Hocko
SUSE Labs
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