oom: thaw the OOM victim if it is frozen

oom_kill_process only sets TIF_MEMDIE flag and sends a signal to the
victim.  This is basically noop when the task is frozen though because the
task sleeps in the uninterruptible sleep.  The victim is eventually thawed
later when oom_scan_process_thread meets the task again in a later OOM
invocation so the OOM killer doesn't live lock.  But this is less than
optimal.

Let's add __thaw_task into mark_tsk_oom_victim after we set TIF_MEMDIE to
the victim.  We are not checking whether the task is frozen because that
would be racy and __thaw_task does that already.  oom_scan_process_thread
doesn't need to care about freezer anymore as TIF_MEMDIE and freezer are
excluded completely now.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 80b34e2..3cbd76b 100644 (file)
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -266,8 +266,6 @@ enum oom_scan_t oom_scan_process_thread(struct task_struct *task,
         * Don't allow any other task to have access to the reserves.
         */
        if (test_tsk_thread_flag(task, TIF_MEMDIE)) {
-               if (unlikely(frozen(task)))
-                       __thaw_task(task);
                if (!force_kill)
                        return OOM_SCAN_ABORT;
        }
@@ -423,6 +421,14 @@ void note_oom_kill(void)
 void mark_tsk_oom_victim(struct task_struct *tsk)
 {
        set_tsk_thread_flag(tsk, TIF_MEMDIE);
+
+       /*
+        * Make sure that the task is woken up from uninterruptible sleep
+        * if it is frozen because OOM killer wouldn't be able to free
+        * any memory and livelock. freezing_slow_path will tell the freezer
+        * that TIF_MEMDIE tasks should be ignored.
+        */
+       __thaw_task(tsk);
 }
 
 /**