Arkadiusz, will you try this patch? >From 48744b6339cf649a69b55997e138c17df1ecc897 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Date: Sat, 26 Jan 2019 20:00:51 +0900 Subject: [PATCH] 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, 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"). Since task_will_free_mem(p) == false if p->mm == NULL, we can assume that p->mm != NULL when wake_oom_reaper() is called from task_will_free_mem() paths. As a side effect of this patch, this patch also avoids enqueuing multiple threads sharing memory via task_will_free_mem(current) path. Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Reported-by: Arkadiusz Miśkiewicz <a.miskiewicz@xxxxxxxxx> Fixes: af8e15cc85a25315 ("oom, oom_reaper: do not enqueue task if it is on the oom_reaper_list head") --- mm/oom_kill.c | 28 +++++++++++++--------------- 1 file changed, 13 insertions(+), 15 deletions(-) diff --git a/mm/oom_kill.c b/mm/oom_kill.c index f0e8cd9..457f240 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -505,14 +505,6 @@ bool __oom_reap_task_mm(struct mm_struct *mm) struct vm_area_struct *vma; bool ret = true; - /* - * Tell all users of get_user/copy_from_user etc... that the content - * is no longer stable. No barriers really needed because unmapping - * should imply barriers already and the reader would hit a page fault - * if it stumbled over a reaped memory. - */ - set_bit(MMF_UNSTABLE, &mm->flags); - for (vma = mm->mmap ; vma; vma = vma->vm_next) { if (!can_madv_dontneed_vma(vma)) continue; @@ -645,10 +637,15 @@ static int oom_reaper(void *unused) return 0; } -static void wake_oom_reaper(struct task_struct *tsk) +static void wake_oom_reaper(struct task_struct *tsk, struct mm_struct *mm) { - /* tsk is already queued? */ - if (tsk == oom_reaper_list || tsk->oom_reaper_list) + /* + * Tell all users of get_user/copy_from_user etc... that the content + * is no longer stable. No barriers really needed because unmapping + * should imply barriers already and the reader would hit a page fault + * if it stumbled over a reaped memory. + */ + if (test_and_set_bit(MMF_UNSTABLE, &mm->flags)) return; get_task_struct(tsk); @@ -668,7 +665,8 @@ static int __init oom_init(void) } subsys_initcall(oom_init) #else -static inline void wake_oom_reaper(struct task_struct *tsk) +static inline void wake_oom_reaper(struct task_struct *tsk, + struct mm_struct *mm) { } #endif /* CONFIG_MMU */ @@ -915,7 +913,7 @@ static void __oom_kill_process(struct task_struct *victim) rcu_read_unlock(); if (can_oom_reap) - wake_oom_reaper(victim); + wake_oom_reaper(victim, mm); mmdrop(mm); put_task_struct(victim); @@ -955,7 +953,7 @@ static void oom_kill_process(struct oom_control *oc, const char *message) task_lock(p); if (task_will_free_mem(p)) { mark_oom_victim(p); - wake_oom_reaper(p); + wake_oom_reaper(p, p->mm); task_unlock(p); put_task_struct(p); return; @@ -1085,7 +1083,7 @@ bool out_of_memory(struct oom_control *oc) */ if (task_will_free_mem(current)) { mark_oom_victim(current); - wake_oom_reaper(current); + wake_oom_reaper(current, current->mm); return true; } -- 1.8.3.1