On 06/14, Ingo Molnar wrote: > > * Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > > > I didn't read v2 yet, but I'd like to ask a question. > > > > Why do we need vmalloc_sync_all()? > > > > It has a single caller, register_die_notifier() which calls it without > > any explanation. IMO, this needs a comment at least. > > Yes, it's used to work around crashes in modular callbacks: if the callbacks > happens to be called from within the page fault path, before the vmalloc page > fault handler runs, then we have a catch-22 problem. > > It's rare but not entirely impossible. But again, the kernel no longer does this? do_page_fault() does vmalloc_fault() without notify_die(). If it fails, I do not see how/why a modular DIE_OOPS handler could try to resolve this problem and trigger another fault. > > I am not sure I understand the changelog in 101f12af correctly, but at first > > glance vmalloc_sync_all() is no longer needed at least on x86, do_page_fault() > > no longer does notify_die(DIE_PAGE_FAULT). And btw DIE_PAGE_FAULT has no users. > > DIE_MNI too... > > > > Perhaps we can simply kill it on x86? > > So in theory we could still have it run from DIE_OOPS, and that could turn a > survivable kernel crash into a non-survivable one. I don't understand... But OK, my understanding of this magic is very limited, please forget. Thanks, Oleg. -- 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>