On Aug 1, 2019, at 11:19 AM, Greg KH <gregkh@linuxfoundation.org> wrote:

On Thu, Aug 01, 2019 at 11:04:14AM -0700, Masoud Sharbiani wrote:

Hey folks,
I’ve 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; Haven’t pinpointed the
exact commit in between 5.2.0 and 5.3-rc1) the offending process goes
into %100 CPU usage, and doesn’t 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