On Mon 26-09-11 17:51:40, Rafael J. Wysocki wrote: > On Monday, September 26, 2011, Michal Hocko wrote: [...] > > From f935ed4558c2fb033ef5c14e02b28e12a615f80e Mon Sep 17 00:00:00 2001 > > From: Michal Hocko <mhocko@xxxxxxx> > > Date: Fri, 16 Sep 2011 11:23:15 +0200 > > Subject: [PATCH] oom: do not live lock on frozen tasks > > > > 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> Thanks. -- 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>