Re: [PATCH] mm, oom: Disable preemption during OOM-kill operation.

[Michal Hocko <mhocko@kernel.org>]

On Sat 19-09-15 16:05:12, Tetsuo Handa wrote:
> Well, this seems to be a problem which prevents me from testing various
> patches that tries to address OOM livelock problem.
> 
> ---------- rcu-stall.c start ----------
> #define _GNU_SOURCE
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <sched.h>
> 
> static int dummy(void *fd)
> {
> 	char c;
> 	/* Wait until the first child thread is killed by the OOM killer. */
> 	read(* (int *) fd, &c, 1);
> 	/* Try to consume as much CPU time as possible via preemption. */
> 	while (1);

You would kill the system by this alone. Having 1000 busy loops just
kills your machine from doing anything useful and you are basically
DoS-ed. I am not sure sprinkling preempt_{enable,disable} all around the
oom path makes much difference. If anything having a kernel high
priority kernel thread sounds like a better approach.

[...]

> 	for (i = 0; i < 1000; i++) {
> 		clone(dummy, malloc(1024) + 1024, CLONE_SIGHAND | CLONE_VM,
> 		      &pipe_fd[0]);
> 		if (!i)
> 			close(pipe_fd[1]);
-- 
Michal Hocko
SUSE Labs

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