Re: [PATCH] mm, oom: show process exiting information in __oom_kill_process()

[Michal Hocko <mhocko@kernel.org>]

On Sun 19-07-20 09:53:15, Yafang Shao wrote:
> When the OOM killer finding a victim and trying to kill it, if the victim
> is already exiting, the task mm will be NULL and no process will be killed.
> But the dump_header() has been already executed, so it will be strange to
> dump so many information without killing a process. We'd better show some
> helpful information to indicate why this happens.
> 
> Suggested-by: David Rientjes <rientjes@google.com>
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
> ---
>  mm/oom_kill.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 6e94962..0480dde 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -863,9 +863,13 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
>  
>  	p = find_lock_task_mm(victim);
>  	if (!p) {
> +		pr_info("Process %d (%s) is already exiting\n",
> +			task_pid_nr(victim), victim->comm);
>  		put_task_struct(victim);

I do agree that a silent bail out is not the best thing to do. The above
message would be more useful if it also explained what the oom killer
does (or does not):

	"OOM victim %d (%s) is already exiting. Skip killing the task\n"

>  		return;
> -	} else if (victim != p) {
> +	}
> +
> +	if (victim != p) {

Why do we need this?

>  		get_task_struct(p);
>  		put_task_struct(victim);
>  		victim = p;
> -- 
> 1.8.3.1

-- 
Michal Hocko
SUSE Labs