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From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	David Rientjes <rientjes@google.com>,
	linux-mm@kvack.org, Yong-Taek Lee <ytk.lee@samsung.com>,
	Paul McKenney <paulmck@linux.vnet.ibm.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] mm, oom: Tolerate processes sharing mm with different view of oom_score_adj.
Date: Sat, 2 Feb 2019 20:06:07 +0900	[thread overview]
Message-ID: <643b94c2-d720-fa95-d6ee-4f0ea6e2686a@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20190201091433.GH11599@dhcp22.suse.cz>

On 2019/02/01 18:14, Michal Hocko wrote:
> On Fri 01-02-19 05:59:55, Tetsuo Handa wrote:
>> On 2019/01/31 16:11, Michal Hocko wrote:
>>> This is really ridiculous. I have already nacked the previous version
>>> and provided two ways around. The simplest one is to drop the printk.
>>> The second one is to move oom_score_adj to the mm struct. Could you
>>> explain why do you still push for this?
>>
>> Dropping printk() does not close the race.
> 
> But it does remove the source of a long operation from the RCU context.
> If you are not willing to post such a trivial patch I will do so.
> 
>> You must propose an alternative patch if you dislike this patch.
> 
> I will eventually get there.
> 

This is really ridiculous. "eventually" cannot be justified as a reason for
rejecting this patch. I want a patch which can be easily backported _now_ .

If vfork() => __set_oom_adj() => execve() sequence is permitted, someone can
try vfork() => clone() => __set_oom_adj() => execve() sequence. And below
program demonstrates that task->vfork_done based exemption in __set_oom_adj()
is broken. It is not always the task_struct who called vfork() that will call
execve().

----------------------------------------
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sched.h>

static int thread1(void *unused)
{
	char *args[3] = { "/bin/true", "true", NULL };
	int fd = open("/proc/self/oom_score_adj", O_WRONLY);
	write(fd, "1000", 4);
	close(fd);
	execve(args[0], args, NULL);
	return 0;
}
int main(int argc, char *argv[])
{
	printf("PID=%d\n", getpid());
	if (vfork() == 0) {
		clone(thread1, malloc(8192) + 8192,
		      CLONE_VM | CLONE_FS | CLONE_FILES, NULL);
		sleep(1);
		_exit(0);
	}
	return 0;
}
----------------------------------------

  PID=8802
  [ 1138.425255] updating oom_score_adj for 8802 (a.out) from 0 to 1000 because it shares mm with 8804 (a.out). Report if this is unexpected.

Current loop to enforce same oom_score_adj is 99%+ ending in vain.
And even your "eventually" will remove this loop.


  reply	other threads:[~2019-02-02 11:06 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-16 10:55 [PATCH] " Tetsuo Handa
2019-01-16 11:09 ` Michal Hocko
2019-01-16 11:30   ` Tetsuo Handa
2019-01-16 12:19     ` Michal Hocko
2019-01-16 13:32       ` Tetsuo Handa
2019-01-16 13:41         ` Michal Hocko
2019-01-17 10:40           ` Tetsuo Handa
2019-01-17 15:51           ` Michal Hocko
2019-01-30 22:49             ` [PATCH v2] " Tetsuo Handa
2019-01-31  7:11               ` Michal Hocko
2019-01-31 20:59                 ` Tetsuo Handa
2019-02-01  9:14                   ` Michal Hocko
2019-02-02 11:06                     ` Tetsuo Handa [this message]
2019-02-11 15:07                       ` Michal Hocko

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