Re: frequent lockups in 3.18rc4

[Linus Torvalds]

On Wed, Nov 19, 2014 at 4:30 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>
> This is why I think that the grsec kernels will crash on very large
> memory systems.  They don't seem to get this right for the kernel
> stack, and a page fault trying to access the stack is a big no-no.

For something like a stack, that's trivial, you could just probe it
before the actual task switch.

So I wouldn't worry about the kernel stack itself (although I think
vmallocing it isn't likely worth it), I'd worry more about some other
random dynamic percpu allocation. Although they arguably shouldn't
happen for low-level code that cannot handle the dynamic
pgd-population. And they generally don't.

It's really tracing that tends to be a special case not because of any
particular low-level code issue, but because instrumenting itself
recursively tends to be a bad idea.

                    Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/