Re: [patch 03/12] mm: oom_kill: switch test-and-clear of known TIF_MEMDIE to clear

Michal Hocko
2015-03-30T14:48:10Z

On Thu 26-03-15 12:50:20, David Rientjes wrote:
[...]
> android, lmk: avoid setting TIF_MEMDIE if process has already exited
>
> TIF_MEMDIE should not be set on a process if it does not have a valid
> ->mm, and this is protected by task_lock().
>
> If TIF_MEMDIE gets set after the mm has detached, and the process fails to
> exit, then the oom killer will defer forever waiting for it to exit.
>
> Make sure that the mm is still valid before setting TIF_MEMDIE by way of
> mark_tsk_oom_victim().

I would prefer if lmk didn't abuse mark_tsk_oom_victim much more. But
this is correct as well.

> Signed-off-by: David Rientjes <rientjes@google.com>

Acked-by: Michal Hocko <mhocko@suse.cz>

> ---
> diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
> --- a/drivers/staging/android/lowmemorykiller.c
> +++ b/drivers/staging/android/lowmemorykiller.c
> @@ -156,20 +156,27 @@ static unsigned long lowmem_scan(struct shrinker *s, struct shrink_control *sc)
> p->pid, p->comm, oom_score_adj, tasksize);
> }
> if (selected) {
> - lowmem_print(1, "send sigkill to %d (%s), adj %hd, size %d\n",
> - selected->pid, selected->comm,
> - selected_oom_score_adj, selected_tasksize);
> - lowmem_deathpending_timeout = jiffies + HZ;
> + task_lock(selected);
> + if (!selected->mm) {
> + /* Already exited, cannot do mark_tsk_oom_victim() */
> + task_unlock(selected);
> + goto out;
> + }
> /*
> * FIXME: lowmemorykiller shouldn't abuse global OOM killer
> * infrastructure. There is no real reason why the selected
> * task should have access to the memory reserves.
> */
> mark_tsk_oom_victim(selected);
> + task_unlock(selected);
> + lowmem_print(1, "send sigkill to %d (%s), adj %hd, size %d\n",
> + selected->pid, selected->comm,
> + selected_oom_score_adj, selected_tasksize);
> + lowmem_deathpending_timeout = jiffies + HZ;
> send_sig(SIGKILL, selected, 0);
> rem += selected_tasksize;
> }
> -
> +out:
> lowmem_print(4, "lowmem_scan %lu, %x, return %lu\n",
> sc->nr_to_scan, sc->gfp_mask, rem);
> rcu_read_unlock();

--
Michal Hocko
SUSE Labs