Messages in this thread | | | Date | Mon, 29 Feb 2016 19:44:44 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH] exit: clear TIF_MEMDIE after exit_task_work |
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On Mon 29-02-16 19:21:31, Michal Hocko wrote: > On Mon 29-02-16 20:02:09, Vladimir Davydov wrote: > > An mm_struct may be pinned by a file. An example is vhost-net device > > created by a qemu/kvm (see vhost_net_ioctl -> vhost_net_set_owner -> > > vhost_dev_set_owner). If such process gets OOM-killed, the reference to > > its mm_struct will only be released from exit_task_work -> ____fput -> > > __fput -> vhost_net_release -> vhost_dev_cleanup, which is called after > > exit_mmap, where TIF_MEMDIE is cleared. As a result, we can start > > selecting the next victim before giving the last one a chance to free > > its memory. In practice, this leads to killing several VMs along with > > the fattest one. > > I am wondering why our PF_EXITING protection hasn't fired up.
OK, I guess I can see it. exit_mm has done tsk->mm = NULL and so we are skipping over that task because oom_scan_process_thread hasn't checked PF_EXITING. I will try to think about this some more tomorrow with a fresh brain. -- Michal Hocko SUSE Labs
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