On Mon, Jun 15, 2015 at 1:28 PM, Ingo Molnar <[email protected]> wrote: > > * Andy Lutomirski <[email protected]> wrote: > >> On Sun, Jun 14, 2015 at 7:47 PM, Andi Kleen <[email protected]> wrote: >> > Oleg Nesterov <[email protected]> writes: >> >> >> >> 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. >> > >> > The same problem can happen from NMI handlers or machine check handlers. >> > It's >> > not necessarily tied to page faults only. >> >> AIUI, the point of the one and only vmalloc_sync_all call is to prevent >> infinitely recursive faults when we call a notify_die callback. The only >> thing >> that it could realistically protect is module text or static non-per-cpu >> module >> data, since that's the only thing that's reliably already in the init pgd. >> I'm >> with Oleg: I don't see how that can happen, since do_page_fault fixes up >> vmalloc >> faults before it calls notify_die. > > Yes, but what I meant is that it can happen if due to an unrelated kernel bug > and > unlucky timing we have installed this new handler just when that other > unrelated > kernel bug triggers: say a #GPF crash in kernel code.
I still don't see the problem. CPU A: crash and start executing do_page_fault CPU B: register_die_notifier CPU A: notify_die now we get a vmalloc fault, fix it up, and return to do_page_fault and print the oops. > > In any case it should all be mooted with the removal of lazy PGD > instantiation. Agreed. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
