On Tue 14-06-16 22:17:40, Oleg Nesterov wrote: > On 06/13, Michal Hocko wrote: > > > > On Mon 13-06-16 13:23:48, Michal Hocko wrote: > > > On Thu 09-06-16 13:52:07, Michal Hocko wrote: > > > > I would like to explore ways how to remove kthreads (use_mm) special > > > > case. It shouldn't be that hard, we just have to teach the page fault > > > > handler to recognize oom victim mm and enforce EFAULT for kthreads > > > > which have borrowed that mm. > > > > > > So I was trying to come up with solution for this which would require to > > > hook into the pagefault an enforce EFAULT when the mm is being reaped > > > by the oom_repaer. Not hard but then I have checked the current users > > > and none of them is really needing to read from the userspace (aka > > > copy_from_user/get_user). So we actually do not need to do anything > > > special. > > > > As pointed out by Tetsuo [1] vhost does realy on copy_from_user. > > Tetsuo, Michal, but do we really care? > > I have no idea what vhost does, but obviously this should not lead to kernel > crash or something like this, otherwise it should be fixed. If we are going > to kill the owner of dev->mm anyway, why should we worry about vhost_worker() > which can fail to access this ->mm after that? This needs a deeper investigation. It relies on some state flags copied from the userspace. I suspect it might misbehave but let's leave this alone for a while. It is more complicated than I expected. -- 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>