For non root CG, in try_charge(), we keep trying to charge until we succeed. On non-preemptive kernel, when we are OOM, this results in holding CPU forever. On SMP systems, this doesn't create a big problem because oom_reaper get a change to kill victim and make some free pages. However on a single-core CPU (or cases where oom_reaper pinned to same CPU where try_charge is executing), oom_reaper shall never get scheduled and we stay in try_charge forever. Steps to repo this on non-smp: 1. mount -t tmpfs none /sys/fs/cgroup 2. mkdir /sys/fs/cgroup/memory 3. mount -t cgroup none /sys/fs/cgroup/memory -o memory 4. mkdir /sys/fs/cgroup/memory/0 5. echo 40M > /sys/fs/cgroup/memory/0/memory.limit_in_bytes 6. echo $$ > /sys/fs/cgroup/memory/0/tasks 7. stress -m 5 --vm-bytes 10M --vm-hang 0 Signed-off-by: Julius Hemanth Pitti <jpitti@xxxxxxxxx> Acked-by: Roman Gushchin <guro@xxxxxx> --- Changes in v2: - Added comments. - Added "Acked-by: Roman Gushchin <guro@xxxxxx>". --- mm/memcontrol.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index cfa6cbad21d5..4f293bf8c7ed 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2745,6 +2745,15 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, if (fatal_signal_pending(current)) goto force; + /* + * We failed to charge even after retries, give oom_reaper or + * other process a change to make some free pages. + * + * On non-preemptive, Non-SMP system, this is critical, else + * we keep retrying with no success, forever. + */ + cond_resched(); + /* * keep retrying as long as the memcg oom killer is able to make * a forward progress or bypass the charge if the oom killer -- 2.17.1
