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

[Michal Hocko <mhocko@suse.cz>]

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

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