When a process is oom killed as a result of memcg limits and the victim is waiting to exit, nothing ends up actually yielding the processor back to the victim on UP systems with preemption disabled. Instead, the charging process simply loops in memcg reclaim and eventually soft lockups. Memory cgroup out of memory: Killed process 808 (repro) total-vm:41944kB, anon-rss:35344kB, file-rss:504kB, shmem-rss:0kB, UID:0 pgtables:108kB oom_score_adj:0 watchdog: BUG: soft lockup - CPU#0 stuck for 23s! [repro:806] CPU: 0 PID: 806 Comm: repro Not tainted 5.6.0-rc5+ #136 RIP: 0010:shrink_lruvec+0x4e9/0xa40 ... Call Trace: shrink_node+0x40d/0x7d0 do_try_to_free_pages+0x13f/0x470 try_to_free_mem_cgroup_pages+0x16d/0x230 try_charge+0x247/0xac0 mem_cgroup_try_charge+0x10a/0x220 mem_cgroup_try_charge_delay+0x1e/0x40 handle_mm_fault+0xdf2/0x15f0 do_user_addr_fault+0x21f/0x420 page_fault+0x2f/0x40 Make sure that once the oom killer has been called that we forcibly yield if current is not the chosen victim regardless of priority to allow for memory freeing. The same situation can theoretically occur in the page allocator, so do this after dropping oom_lock there as well. Suggested-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Tested-by: Robert Kolchmeyer <rkolchmeyer@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx> --- mm/memcontrol.c | 2 ++ mm/page_alloc.c | 2 ++ 2 files changed, 4 insertions(+) diff --git a/mm/memcontrol.c b/mm/memcontrol.c --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1576,6 +1576,8 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask, */ ret = should_force_charge() || out_of_memory(&oc); mutex_unlock(&oom_lock); + if (!fatal_signal_pending(current)) + schedule_timeout_killable(1); return ret; } diff --git a/mm/page_alloc.c b/mm/page_alloc.c --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3861,6 +3861,8 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order, } out: mutex_unlock(&oom_lock); + if (!fatal_signal_pending(current)) + schedule_timeout_killable(1); return page; }
