On Wed 27-03-13 18:22:10, David Rientjes wrote: > A memcg may livelock when oom if the process that grabs the hierarchy's > oom lock is never the first process with PF_EXITING set in the memcg's > task iteration. > > The oom killer, both global and memcg, will defer if it finds an eligible > process that is in the process of exiting and it is not being ptraced. > The idea is to allow it to exit without using memory reserves before > needlessly killing another process. > > This normally works fine except in the memcg case with a large number of > threads attached to the oom memcg. In this case, the memcg oom killer > only gets called for the process that grabs the hierarchy's oom lock; all > others end up blocked on the memcg's oom waitqueue. Thus, if the process > that grabs the hierarchy's oom lock is never the first PF_EXITING process > in the memcg's task iteration, the oom killer is constantly deferred > without anything making progress. > > The fix is to give PF_EXITING processes access to memory reserves so that > we've marked them as oom killed without any iteration. This allows > __mem_cgroup_try_charge() to succeed so that the process may exit. This > makes the memcg oom killer exemption for TIF_MEMDIE tasks, now > immediately granted for processes with pending SIGKILLs and those in the > exit path, to be equivalent to what is done for the global oom killer. > > Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxx> AFAIU this has been introduced by 9ff4868e (mm, oom: allow exiting threads to have access to memory reserves) so maybe we want to mark it for stable (3.8). Thanks > --- > mm/memcontrol.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1686,11 +1686,11 @@ static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask, > struct task_struct *chosen = NULL; > > /* > - * If current has a pending SIGKILL, then automatically select it. The > - * goal is to allow it to allocate so that it may quickly exit and free > - * its memory. > + * If current has a pending SIGKILL or is exiting, then automatically > + * select it. The goal is to allow it to allocate so that it may > + * quickly exit and free its memory. > */ > - if (fatal_signal_pending(current)) { > + if (fatal_signal_pending(current) || current->flags & PF_EXITING) { > set_thread_flag(TIF_MEMDIE); > return; > } -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>