Michal Hocko wrote:
> @@ -766,15 +797,12 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
> * If the task is already exiting, don't alarm the sysadmin or kill
> * its children or threads, just set TIF_MEMDIE so it can die quickly
> */
> - task_lock(p);
> - if (p->mm && task_will_free_mem(p)) {
> + if (task_will_free_mem(p)) {
I think it is possible that p->mm becomes NULL here.
Also, I think setting TIF_MEMDIE on p when find_lock_task_mm(p) != p is
wrong. While oom_reap_task() will anyway clear TIF_MEMDIE even if we set
TIF_MEMDIE on p when p->mm == NULL, it is not true for CONFIG_MMU=n case.
> mark_oom_victim(p);
> - try_oom_reaper(p);
> - task_unlock(p);
> + wake_oom_reaper(p);
> put_task_struct(p);
> return;
> }
> - task_unlock(p);
>
> if (__ratelimit(&oom_rs))
> dump_header(oc, p);
> @@ -940,14 +968,10 @@ bool out_of_memory(struct oom_control *oc)
> * If current has a pending SIGKILL or is exiting, then automatically
> * select it. The goal is to allow it to allocate so that it may
> * quickly exit and free its memory.
> - *
> - * But don't select if current has already released its mm and cleared
> - * TIF_MEMDIE flag at exit_mm(), otherwise an OOM livelock may occur.
> */
> - if (current->mm &&
> - (fatal_signal_pending(current) || task_will_free_mem(current))) {
> + if (task_will_free_mem(current)) {
Setting TIF_MEMDIE on current when current->mm == NULL and
find_lock_task_mm(current) != NULL is wrong.
> mark_oom_victim(current);
> - try_oom_reaper(current);
> + wake_oom_reaper(current);
> return true;
> }
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