Messages in this thread | | | Date | Thu, 11 Sep 2014 18:30:04 +0200 | From | Michal Hocko <> | Subject | Re: [Patch v4 1/2] freezer: check OOM kill while being frozen |
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On Wed 10-09-14 13:30:25, Cong Wang wrote: > On Mon, Sep 8, 2014 at 4:29 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote: > > On Mon, Sep 8, 2014 at 4:42 PM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote: > >> On Monday, September 08, 2014 04:16:15 PM Cong Wang wrote: > >>> On Mon, Sep 8, 2014 at 4:23 PM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote: > >>> > > >>> > The reason why it matters for the suspend-time freezing is that we freeze tasks > >>> > to take them out of the picture entirely until they are thawed. Therefore we > >>> > can't allow them to go back to the picture just for a while until they are > >>> > killed. Frozen tasks are not supposed to get back to the picture at all. > >>> > > >>> > >>> > >>> Ok, then checking TIF_MEMDIE is unsafe for PM freeze, we should > >>> keep the cgroup_freezing() test to make sure freeze request is from > >>> cgroup not PM. Question got answered. :) > >> > >> Do I think correctly that cgroups freezing and system suspend are > >> mutually exclusive? If not, then this still is problematic. > > > > Good point! Although rare, but it is possible we freeze a process both from > > cgroup and PM. Hmm, this means we have to explicitly exclude PM rather > > just checking cgroup freeze? Interesting, but I am not familiar with PM. > > > > I am wondering if the folllowing check makes any sense with regarding > to rule out PM freeze: > > if ((!pm_nosig_freezing && !pm_freezing) && > cgroup_freezing(current) && test_thread_flag(TIF_MEMDIE)) > return true;
Why is this needed in the first place? What if OOM happens in the middle of task freezing during freeze_processes? Also killing a task at that stage should be safe as no devices are suspended yet and OOM killer is disabled after all tasks are frozen and allocations fail at that stage. -- Michal Hocko SUSE Labs
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