Re: [PULL] vhost: cleanups and fixes

From: Linus Torvalds
Date: Mon Jun 11 2018 - 14:44:33 EST

On Mon, Jun 11, 2018 at 11:32 AM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> So now we apparently do a GFP_KERNEL allocation insider the mm zone
> lock, which is broken on just _so_ many levels.

Oh, I see the comment about how it doesn't actually do an allocation
at all because it's a single-entry.

Still too damn ugly to live, and much too fragile. No way in hell do
we even _hint_ at a GFP_KERNEL when we're inside a context that can't
do any memory allocation at all.

Plus I'm not convinced it's a "no allocation" path even despite that
comment, because it also does a "dma_map_page()" etc, which can cause
allocations to do the dma mapping thing afaik. No?

Maybe there's some reason why that doesn't happen either, but
basically this whole callchain looks *way* to complicated to be used
under a core VM spinlock.