On Mon 26-09-11 18:03:26, David Rientjes wrote: > On Mon, 26 Sep 2011, Rafael J. Wysocki wrote: > > > > Konstantin Khlebnikov has reported (https://lkml.org/lkml/2011/8/23/45) > > > that OOM can end up in a live lock if select_bad_process picks up a frozen > > > task. > > > Unfortunately we cannot mark such processes as unkillable to ignore them > > > because we could panic the system even though there is a chance that > > > somebody could thaw the process so we can make a forward process (e.g. a > > > process from another cpuset or with a different nodemask). > > > > > > Let's thaw an OOM selected frozen process right after we've sent fatal > > > signal from oom_kill_task. > > > Thawing is safe if the frozen task doesn't access any suspended device > > > (e.g. by ioctl) on the way out to the userspace where we handle the > > > signal and die. Note, we are not interested in the kernel threads because > > > they are not oom killable. > > > > > > Accessing suspended devices by a userspace processes shouldn't be an > > > issue because devices are suspended only after userspace is already > > > frozen and oom is disabled at that time. > > > > > > run_guest (drivers/lguest/core.c) calls try_to_freeze with an user > > > context but it seems it is able to cope with signals because it > > > explicitly checks for pending signals so we should be safe. > > > > > > Other than that userspace accesses the fridge only from the > > > signal handling routines so we are able to handle SIGKILL without any > > > negative side effects. > > > > > > Signed-off-by: Michal Hocko <mhocko@xxxxxxx> > > > Reported-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx> > > > > Acked-by: Rafael J. Wysocki <rjw@xxxxxxx> > > > > Acked-by: David Rientjes <rientjes@xxxxxxxxxx> Thanks! > > Although this still seems to be problematic if the chosen thread gets > frozen before the SIGKILL can be handled. We don't have any checks for > fatal_signal_pending() when freezing threads and waiting for them to exit? I guess you mean a situation when select_bad_process picks up a process which is not marked as frozen yet but we send SIGKILL right before schedule is called in refrigerator. In that case either schedule should catch it by signal_pending_state check or we will pick it up next OOM round when we pick up the same process (if nothing else is eligible). Or am I missing something? > Michal, could you send Andrew your revised patch with all the acked-bys? Yes I will. I would just like to hear back from Konstantin who originally reported the issue. Maybe he has a test case. > > Thanks! > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>