Re: frequent lockups in 3.18rc4

[Linus Torvalds]

On Fri, Nov 21, 2014 at 11:23 AM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> Should we at least check to see if it is present?
>
>         if (!(pgd_entry & 1))
>                 return -1;

Maybe. But what other entry could there be?

But yes, returning -1 is "safe", since it basically says "I'm not
doing a vmalloc thing, oops if this is a bad access". So that kind of
argues for being as aggressive as possible in returning 1.

So for the first one (!pgd_entry), instead of returning -1 only for a
completely empty entry, returning it for any non-present case is
probably right.

And for the second one (where we check whether there is anything at
all in the destination), returning -1 for "anything but zero" is
probably the right thing to do.

But in the end, if you have a corrupted top-level kernel page table,
it sounds to me like you're just royally screwed anyway. So I don't
think it matters *that* much.

So I kind of agree, but it wouldn't be my primary worry. My primary
worry is actually paravirt doing something insane.

                    Linus
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