Re: WARNING in try_charge

Tetsuo Handa
2018-08-06T20:46:13Z

On 2018/08/07 5:34, Michal Hocko wrote:
> On Tue 07-08-18 05:26:23, Tetsuo Handa wrote:
>> On 2018/08/07 2:56, Michal Hocko wrote:
>>> So the oom victim indeed passed the above force path after the oom
>>> invocation. But later on hit the page fault path and that behaved
>>> differently and for some reason the force path hasn't triggered. I am
>>> wondering how could we hit the page fault path in the first place. The
>>> task is already killed! So what the hell is going on here.
>>>
>>> I must be missing something obvious here.
>>>
>> YOU ARE OBVIOUSLY MISSING MY MAIL!
>>
>> I already said this is "mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for once."
>> problem which you are refusing at https://www.spinics.net/lists/linux-mm/msg133774.html .
>> And you again ignored my mail. Very sad...
>
> Your suggestion simply didn't make much sense. There is nothing like
> first check is different from the rest.
>

I don't think your patch is appropriate. It avoids hitting WARN(1) but does not avoid
unnecessary killing of OOM victims.

If you look at https://syzkaller.appspot.com/text?tag=CrashLog&x=15a1c770400000 , you will
notice that both 23766 and 23767 are killed due to task_will_free_mem(current) == false.
This is "unnecessary killing of additional processes".

[ 365.869417] syz-executor2 invoked oom-killer: gfp_mask=0x6000c0(GFP_KERNEL), order=0, oom_score_adj=0
[ 365.878899] CPU: 0 PID: 23767 Comm: syz-executor2 Not tainted 4.18.0-rc6-next-20180725+ #18
(...snipped...)
[ 366.487490] Tasks state (memory values in pages):
[ 366.492349] [ pid ] uid tgid total_vm rss pgtables_bytes swapents oom_score_adj name
[ 366.501237] [ 23766] 0 23766 17620 8221 126976 0 0 syz-executor3
[ 366.510367] [ 23767] 0 23767 17618 8218 126976 0 0 syz-executor2
[ 366.519409] Memory cgroup out of memory: Kill process 23766 (syz-executor3) score 8252000 or sacrifice child
[ 366.529422] Killed process 23766 (syz-executor3) total-vm:70480kB, anon-rss:116kB, file-rss:32768kB, shmem-rss:0kB
[ 366.540456] oom_reaper: reaped process 23766 (syz-executor3), now anon-rss:0kB, file-rss:32000kB, shmem-rss:0kB
[ 366.550949] syz-executor3 invoked oom-killer: gfp_mask=0x6000c0(GFP_KERNEL), order=0, oom_score_adj=0
[ 366.560374] CPU: 1 PID: 23766 Comm: syz-executor3 Not tainted 4.18.0-rc6-next-20180725+ #18
(...snipped...)
[ 367.138136] Tasks state (memory values in pages):
[ 367.142986] [ pid ] uid tgid total_vm rss pgtables_bytes swapents oom_score_adj name
[ 367.151889] [ 23766] 0 23766 17620 8002 126976 0 0 syz-executor3
[ 367.160946] [ 23767] 0 23767 17618 8218 126976 0 0 syz-executor2
[ 367.169994] Memory cgroup out of memory: Kill process 23767 (syz-executor2) score 8249000 or sacrifice child
[ 367.180119] Killed process 23767 (syz-executor2) total-vm:70472kB, anon-rss:104kB, file-rss:32768kB, shmem-rss:0kB
[ 367.192101] oom_reaper: reaped process 23767 (syz-executor2), now anon-rss:0kB, file-rss:32000kB, shmem-rss:0kB
[ 367.202986] ------------[ cut here ]------------
[ 367.207845] Memory cgroup charge failed because of no reclaimable memory! This looks like a misconfiguration or a kernel bug.
[ 367.207965] WARNING: CPU: 1 PID: 23767 at mm/memcontrol.c:1710 try_charge+0x734/0x1680
[ 367.227540] Kernel panic - not syncing: panic_on_warn set ...