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

[Greg KH]

On Thu, Aug 01, 2019 at 11:04:14AM -0700, Masoud Sharbiani wrote:
> Hey folks,
> Iâve come across an issue that affects most of 4.19, 4.20 and 5.2 linux-stable kernels that has only been fixed in 5.3-rc1.
> It was introduced by
> 
> 29ef680 memcg, oom: move out_of_memory back to the charge path 
> 
> The gist of it is that if you have a memory control group for a process that repeatedly maps all of the pages of a file with  repeated calls to:
> 
>    mmap(NULL, pages * PAGE_SIZE, PROT_WRITE|PROT_READ, MAP_FILE|MAP_PRIVATE, fd, 0)
> 
> The memory cg eventually runs out of memory, as it should. However,
> prior to the 29ef680 commit, it would kill the running process with
> OOM; After that commit ( and until 5.3-rc1; Havenât pinpointed the
> exact commit in between 5.2.0 and 5.3-rc1) the offending process goes
> into %100 CPU usage, and doesnât die (prior behavior) or fail the mmap
> call (which is what happens if one runs the test program with a low
> ulimit -v value).
> 
> Any ideas on how to chase this down further?

Finding the exact patch that fixes this would be great, as then I can
add it to the 4.19 and 5.2 stable kernels (4.20 is long end-of-life, no
idea why you are messing with that one...)

thanks,

greg k-h