OOM killer hung the whole system

[Mulyadi Santosa]

On Tue, Jul 25, 2017 at 4:59 PM, Rock Lee <rockdotlee at gmail.com> wrote:

> Hi,
>
> I was using a program to test OOM killer, but OOM killer hung my board.
> The test snippet is very simple, just malloc() without free().
>
>   6         int i=0;
>   7         char *ptrtest=NULL;
>   8          while (1)
>   9          {
>  10                    ptrtest = malloc(0x1000);
>  11                    if (ptrtest == NULL)
>  12                        printf("malloc failed.\n");
>  13          }
>  14          return 0;
>  15
>
> After I executed this program(a.out), there is no reaction of my shell.
> Only this messege was shown:
>
> [  180.138188] Out of memory: Kill process 2706 (qq) score 623 or
> sacrifice child
> [  180.164230] Killed process 2706 (qq) total-vm:98156kB,
> anon-rss:96400kB, file-rss:4kB
>
>
I think the clue is above. Could you find out what is the process with pid
2706?

I bet that is the shell that runs as the parent of your a.out program, but
feel free to make sure what that is.



> I think it must be some problem with OOM killer, and tried a lot of way to
> get some infomation. And I got this:
>
> =======================================================
> Process: a.out, cpu: 0 pid: 1463 start: 0xd5849b00
> =====================================================
>     Task name: a.out pid: 1463 cpu: 0
>     state: 0x2 exit_state: 0x0 stack base: 0xd6190000
>     Stack:
>     [<c08394e4>] __schedule+0x2c8
>     [<c018df88>] squashfs_cache_get+0x108
>     [<c0191020>] squashfs_readpage_block+0x28
>     [<c018f648>] squashfs_readpage+0x624
>     [<c0090d4c>] __do_page_cache_readahead+0x228
>     [<c00882f4>] filemap_fault+0x1d4
>     [<c00a5f10>] __do_fault+0x34
>     [<c00a8ab0>] do_read_fault+0x19c
>     [<c00a9388>] handle_mm_fault+0x468
>     [<c00164b0>] do_page_fault+0x11c
>     [<c00084a4>] do_PrefetchAbort+0x34
>     [<c0011c1c>] ret_from_exception+0x0
>
> I am suprised, because a.out is in /tmp, there is no relation between
> a.out and squashfs(my rootfs). Could anyone give me a hint ? Is the problem
> of squashfs or OOM killer.
>

The above stack trace just mention what happened in kernel space. Very
likely when it was about to be killled by OOM killer. CMIIW.

Thus, it has little or nothing to do with the fact that it called squash fs
related function


-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

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