On Thu, Aug 5, 2021 at 11:40 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > On Thu 05-08-21 10:08:58, Suren Baghdasaryan wrote: > [...] > > + /* > > + * If the task is dying and in the process of releasing its memory > > + * then get its mm. > > + */ > > + p = find_lock_task_mm(task); > > + if (!p) { > > + ret = -ESRCH; > > + goto put_pid; > > + } > > + if (task != p) { > > + get_task_struct(p); > > + put_task_struct(task); > > + task = p; > > + } > > Why do you need to take a reference to the p here? You are under > task_lock so this will not go away and you only need p to get your mm. True. > > > + > > + /* If the work has been done already, just exit with success */ > > + if (test_bit(MMF_OOM_SKIP, &task->mm->flags)) > > + goto put_task; > > You want to release the task_lock Missed it again :( > > > + > > + if (task_will_free_mem(task) && (task->flags & PF_KTHREAD) == 0) { > > you want task_will_free_mem(p) and what is the point of the PF_KTHREAD > check? Yeah, looks like task_will_free_mem() covers that case already. > > > + mm = task->mm; > > + mmget(mm); > > All you need is to make sure mm will not get released under your feet > once task_lock is released so mmgrab is the right thing to do here. The > address space can be torn down in parallel and that is OK and desirable. > > I think you really want something like this: > > if (flags) > return -EINVAL; > > pid = pidfd_get_pid(fd, &f_flags); > if (IS_ERR(pid)) > return PTR_ERR(pid); > task = get_pid_task(pid, PIDTYPE_PID); > if (!task) { > ret = -ESRCH; > goto put_pid; > } > > /* > * Make sure to chose a thread which still has a reference to mm > * during the group exit > */ > p = find_lock_task_mm(task); > if (!p) { > ret = -ESRCH; > goto put_task; > } > > mm = task->mm; > mmgrab(mm); > reap = true; > /* If the work has been done already, just exit with success */ > if (test_bit(MMF_OOM_SKIP, &mm->flags)) { > reap = false; > } else if (!task_will_free_mem(p)) { > reap = false; > ret = -EINVAL; > } > task_unlock(p); > > if (!reap) > goto dropmm;; > > /* Do the work*/ > > > dropmm: > mmdrop(mm); > put_task: > put_task(task); > put_pid: > put_pid(pid); > > return ret; > This is indeed simpler to follow. I'll adopt your version. Thanks! > -- > Michal Hocko > SUSE Labs