oom, oom_reaper: do not enqueue same task twice

Arkadiusz reported that enabling memcg's group oom killing causes strange memcg statistics where there is no task in a memcg despite the number of tasks in that memcg is not 0. It turned out that there is a bug in wake_oom_reaper() which allows enqueuing same task twice which makes impossible to decrease the number of tasks in that memcg due to a refcount leak. This bug existed since the OOM reaper became invokable from task_will_free_mem(current) path in out_of_memory() in Linux 4.7, T1@P1 |T2@P1 |T3@P1 |OOM reaper ----------+----------+----------+------------ # Processing an OOM victim in a different memcg domain. try_charge() mem_cgroup_out_of_memory() mutex_lock(&oom_lock) try_charge() mem_cgroup_out_of_memory() mutex_lock(&oom_lock) try_charge() mem_cgroup_out_of_memory() mutex_lock(&oom_lock) out_of_memory() oom_kill_process(P1) do_send_sig_info(SIGKILL, @P1) mark_oom_victim(T1@P1) wake_oom_reaper(T1@P1) # T1@P1 is enqueued. mutex_unlock(&oom_lock) out_of_memory() mark_oom_victim(T2@P1) wake_oom_reaper(T2@P1) # T2@P1 is enqueued. mutex_unlock(&oom_lock) out_of_memory() mark_oom_victim(T1@P1) wake_oom_reaper(T1@P1) # T1@P1 is enqueued again due to oom_reaper_list == T2@P1 && T1@P1->oom_reaper_list == NULL. mutex_unlock(&oom_lock) # Completed processing an OOM victim in a different memcg domain. spin_lock(&oom_reaper_lock) # T1P1 is dequeued. spin_unlock(&oom_reaper_lock) but memcg's group oom killing made it easier to trigger this bug by calling wake_oom_reaper() on the same task from one out_of_memory() request. Fix this bug using an approach used by commit 855b018325737f76 ("oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task"). As a side effect of this patch, this patch also avoids enqueuing multiple threads sharing memory via task_will_free_mem(current) path.

Tetsuo Handa committed 7 years ago

Commit 9bcdeb51 parent 80409c62 files · +3 −2Browse files

Unified · Split

2 files

include/linux/sched/coredump.h +1 −0
mm/oom_kill.c +2 −2

include/linux/sched/coredump.h+1−0

@@ -71,6 +71,7 @@ static inline int get_dumpable(struct mm_struct *mm) · 70 unmodified lines
71	71	#define MMF_HUGE_ZERO_PAGE 23 /* mm has ever used the global huge zero page */
72	72	#define MMF_DISABLE_THP 24 /* disable THP for all VMAs */
73	73	#define MMF_OOM_VICTIM 25 /* mm is the oom victim */
	74	+#define MMF_OOM_REAP_QUEUED 26 /* mm was queued for oom_reaper */
74	75	#define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP)
75	76
76	77	#define MMF_INIT_MASK (MMF_DUMPABLE_MASK \| MMF_DUMP_FILTER_MASK \|\

mm/oom_kill.c+2−2

@@ -647,8 +647,8 @@ static int oom_reaper(void *unused) · 646 unmodified lines
647	647
648	648	static void wake_oom_reaper(struct task_struct *tsk)
649	649	{
650		− /* tsk is already queued? */
651		− if (tsk == oom_reaper_list \|\| tsk->oom_reaper_list)
	650	+ /* mm is already queued? */
	651	+ if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags))
652	652	return;
653	653
654	654	get_task_struct(tsk);