On Thu 24-10-19 01:33:01, Qian Cai wrote: > > > > On Oct 23, 2019, at 6:30 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > Yes, removing things is hard. One approach is to add printk_once(this > > is going away, please email us if you use it) then wait a few years. > > Backport that one-liner into -stable kernels to hopefully speed up the > > process. > > Although it still look like an overkill to me given, > > 1) Mel given a green light to remove it. > 2) Nobody justifies any sensible reason to keep it apart from it was > probably only triggering by some testing tools blindly read procfs > entries. It's been useful for debugging memory fragmentation problems and we do not have anything that would provide a similar information. Considering that making it root only is trivial and reducing the lock hold times likewise I do not really see any strong reason to dump it at this moment. > it is still better than wasting developers’ time to beating the “dead” horse. > > > > > Meanwhile, we need to fix the DoS opportunity. How about my suggestion > > that we limit the count to 1024, see if anyone notices? I bet they > > don't! > > The DoS is probably there since the file had been introduced almost 10 > years ago, so I suspect it is not that easily exploitable. Yes you need _tons_ of memory. Reading the file on my 3TB system takes sys 0m3.673s The situation might be worse if the system is terribly fragmented which is not the case here. -- Michal Hocko SUSE Labs
