On Tue, Jul 04, 2017 at 11:37:15AM -0700, Linus Torvalds wrote: > On Tue, Jul 4, 2017 at 10:22 AM, Michal Hocko <[email protected]> wrote: > > > > Well, I've been thinking about this some more and the more I think about > > it the less I am convinced we should try to be clever here. Why? Because > > as soon as somebody tries to manage stacks explicitly you cannot simply > > assume anything about the previous mapping. Say some interpret uses > > [ mngmnt data][red zone] <--[- MAP_GROWSDOWN ] > > > > Now if we consider the red zone's (PROT_NONE) prev mapping we would fail > > the expansion even though we haven't hit the red zone and that is > > essentially what the Java and rust bugs are about. So we just risk yet > > another regression. > > Ack. > > Let's make the initial version at least only check the first vma. > > The long-term fix for this is to have the binaries do proper stack > expansion probing anyway, and it's quite possible that people who do > their own stack redzoning by adding a PROT_NONE thing already do that > proper fix (eg the Java stack may simply not *have* those big crazy > structures on it in the first place).
But what is wrong with stopping the loop as soon as the distance gets larger than the stack_guard_gap ? Willy
