linux-kernel - Re: [RFC] EPOLL_KILLME: New flag to epoll_wait() that subscribes process to death row (new syscall)

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Message-ID: <b98ae797-ce25-79bd-e405-35565256f673@I-love.SAKURA.ne.jp>
Date:   Thu, 2 Nov 2017 07:10:24 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Shawn Landden <slandden@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [RFC] EPOLL_KILLME: New flag to epoll_wait() that subscribes
 process to death row (new syscall)

On 2017/11/01 14:32, Shawn Landden wrote:
> @@ -1029,6 +1030,22 @@ bool out_of_memory(struct oom_control *oc)
>  		return true;
>  	}
>  
> +	/*
> +	 * Check death row.
> +	 */
> +	if (!list_empty(eventpoll_deathrow_list())) {
> +		struct list_head *l = eventpoll_deathrow_list();

Unsafe traversal. List can become empty at this moment.

> +		struct task_struct *ts = list_first_entry(l,
> +					 struct task_struct, se.deathrow);
> +
> +		pr_debug("Killing pid %u from EPOLL_KILLME death row.",
> +			ts->pid);
> +
> +		/* We use SIGKILL so as to cleanly interrupt ep_poll() */
> +		kill_pid(task_pid(ts), SIGKILL, 1);

send_sig() ?

> +		return true;
> +	}
> +
>  	/*
>  	 * The OOM killer does not compensate for IO-less reclaim.
>  	 * pagefault_out_of_memory lost its gfp context so we have to
> 

And why is

  static int oom_fd = open("/proc/self/oom_score_adj", O_WRONLY);

and then toggling between

  write(fd, "1000", 4);

and

  write(fd, "0", 1);

not sufficient? Adding prctl() that do this might be handy though.