On 08/25, Hugh Dickins wrote: > > On Mon, 25 Aug 2014, Oleg Nesterov wrote: > > On 08/24, Hugh Dickins wrote: > > > > > > I'd say it comes earlier, from Christoph Rohland's 2.4.17-pre7's > > > "Add missing checks on shmat()", though I didn't find more than that. > > > > > > We can all understand wanting to leave a gap below the growsdown stack, > > > but of course could argue about growsup and 1 or 4 or 5 or whatever: > > > > And it is not clear to me why the kernel should care at all, > > Care about what exactly? Leaving a gap between shm and stack? > > The man page says that (unless SHM_REMAP) shmat() will fail with > EINVAL if a mapping already exists there, and I think it's fair > to regard the vm_start of a VM_GROWSDOWN somewhat elastically. > > It may be that Linus's check_stack_guard_page() work in 2.6.36 > changed the importance of this shmat() check, but I'd still feel > safer to leave it as is (while turning a blind eye to the > VM_GROWSUP omission). > > > > > > okay that we're all more interested in just removing that start_stack. > > > > so perhaps v2 should simply remove it? Or do you think it would be safer > > to not do this? > > It would be safer to leave it, but replace the start_stack use as you did.
OK, thanks. > And I think I'll let Linus's guard page justify your 4 (to match comment) > in place of the original's mysterious 5. Ah, thanks again. Yes, if we want to guarantee 4 pages we should check 5. Although obviously this doesn't explain the original's 5, this was written before check_stack_guard_page(). OK. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
