On Mon, Jun 15, 2015 at 1:28 PM, Ingo Molnar <mingo@xxxxxxxxxx> wrote: > > * Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > >> On Sun, Jun 14, 2015 at 7:47 PM, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote: >> > Oleg Nesterov <oleg@xxxxxxxxxx> 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, 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>