Re: Possible mem cgroup bug in kernels between 4.18.0 and 5.3-rc1.

[Masoud Sharbiani]

> On Aug 3, 2019, at 10:41 AM, Masoud Sharbiani <msharbiani@xxxxxxxxx> wrote:
> 
> 
> 
>> On Aug 3, 2019, at 8:51 AM, Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
>> 
>> Masoud, will you try this patch?
> 
> Gladly.
> It looks like it is working (and OOMing properly).
> 
> 
>> 
>> By the way, is /sys/fs/cgroup/memory/leaker/memory.usage_in_bytes remains non-zero
>> despite /sys/fs/cgroup/memory/leaker/tasks became empty due to memcg OOM killer expected?
>> Deleting big-data-file.bin after memcg OOM killer reduces some, but still remains
>> non-zero.
> 
> Yes. I had not noticed that:
> 
> [ 1114.190477] oom_reaper: reaped process 1942 (leaker), now anon-rss:0kB, file-
> rss:0kB, shmem-rss:0kB
> ./test-script.sh: line 16:  1942 Killed                  ./leaker -p 10240 -c 100000
> 
> [root@localhost laleaker]# cat  /sys/fs/cgroup/memory/leaker/memory.usage_in_bytes
> 3194880
> [root@localhost laleaker]# cat  /sys/fs/cgroup/memory/leaker/memory.limit_in_bytes
> 536870912
> [root@localhost laleaker]# rm -f big-data-file.bin
> [root@localhost laleaker]# cat  /sys/fs/cgroup/memory/leaker/memory.usage_in_bytes
> 2838528
> 
> Thanks!
> Masoud
> 
> PS: Tried hand-back-porting it to 4.19-y and it didnât work. I think there are other patches between 4.19.0 and 5.3 that could be necessaryâ
> 

Please ignore this last part. It works on 4.19-y branch as well. 

Masoud

> 
>> 
>> ----------------------------------------
>> From 2f92c70f390f42185c6e2abb8dda98b1b7d02fa9 Mon Sep 17 00:00:00 2001
>> From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
>> Date: Sun, 4 Aug 2019 00:41:30 +0900
>> Subject: [PATCH] memcg, oom: don't require __GFP_FS when invoking memcg OOM killer
>> 
>> Masoud Sharbiani noticed that commit 29ef680ae7c21110 ("memcg, oom: move
>> out_of_memory back to the charge path") broke memcg OOM called from
>> __xfs_filemap_fault() path. It turned out that try_chage() is retrying
>> forever without making forward progress because mem_cgroup_oom(GFP_NOFS)
>> cannot invoke the OOM killer due to commit 3da88fb3bacfaa33 ("mm, oom:
>> move GFP_NOFS check to out_of_memory"). Regarding memcg OOM, we need to
>> bypass GFP_NOFS check in order to guarantee forward progress.
>> 
>> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
>> Reported-by: Masoud Sharbiani <msharbiani@xxxxxxxxx>
>> Bisected-by: Masoud Sharbiani <msharbiani@xxxxxxxxx>
>> Fixes: 29ef680ae7c21110 ("memcg, oom: move out_of_memory back to the charge path")
>> ---
>> mm/oom_kill.c | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>> 
>> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
>> index eda2e2a..26804ab 100644
>> --- a/mm/oom_kill.c
>> +++ b/mm/oom_kill.c
>> @@ -1068,9 +1068,10 @@ bool out_of_memory(struct oom_control *oc)
>> 	 * The OOM killer does not compensate for IO-less reclaim.
>> 	 * pagefault_out_of_memory lost its gfp context so we have to
>> 	 * make sure exclude 0 mask - all other users should have at least
>> -	 * ___GFP_DIRECT_RECLAIM to get here.
>> +	 * ___GFP_DIRECT_RECLAIM to get here. But mem_cgroup_oom() has to
>> +	 * invoke the OOM killer even if it is a GFP_NOFS allocation.
>> 	 */
>> -	if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS))
>> +	if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS) && !is_memcg_oom(oc))
>> 		return true;
>> 
>> 	/*
>> -- 
>> 1.8.3.1
>> 
>> 
>