oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task

Tetsuo has reported that oom_kill_allocating_task=1 will cause
oom_reaper_list corruption because oom_kill_process doesn't follow
standard OOM exclusion (aka ignores TIF_MEMDIE) and allows to enqueue
the same task multiple times - e.g.  by sacrificing the same child
multiple times.

This patch fixes the issue by introducing a new MMF_OOM_KILLED mm flag
which is set in oom_kill_process atomically and oom reaper is disabled
if the flag was already set.

Signed-off-by: Michal Hocko <[email protected]>
Reported-by: Tetsuo Handa <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Rik van Riel <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/sched.h

@@ -512,6 +512,8 @@ static inline int get_dumpable(struct mm_struct *mm)
 #define MMF_HAS_UPROBES		19	/* has uprobes */
 #define MMF_RECALC_UPROBES	20	/* MMF_HAS_UPROBES can be wrong */
 
+#define MMF_OOM_KILLED		21	/* OOM killer has chosen this mm */
+
 #define MMF_INIT_MASK		(MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)
 
 struct sighand_struct {

mm/oom_kill.c

@@ -680,7 +680,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
 	unsigned int victim_points = 0;
 	static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
 					      DEFAULT_RATELIMIT_BURST);
-	bool can_oom_reap = true;
+	bool can_oom_reap;
 
 	/*
 	 * If the task is already exiting, don't alarm the sysadmin or kill
@@ -742,6 +742,10 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
 	/* Get a reference to safely compare mm after task_unlock(victim) */
 	mm = victim->mm;
 	atomic_inc(&mm->mm_count);
+
+	/* Make sure we do not try to oom reap the mm multiple times */
+	can_oom_reap = !test_and_set_bit(MMF_OOM_KILLED, &mm->flags);
+
 	/*
 	 * We should send SIGKILL before setting TIF_MEMDIE in order to prevent
 	 * the OOM victim from depleting the memory reserves from the user