Re: [PATCH V5 0/9] Fixes for vhost metadata acceleration

On 2019/8/14 上午12:41, Christoph Hellwig wrote:

On Tue, Aug 13, 2019 at 08:57:07AM -0300, Jason Gunthorpe wrote:

quoted

On Tue, Aug 13, 2019 at 04:31:07PM +0800, Jason Wang wrote:

quoted

What kind of issues do you see? Spinlock is to synchronize GUP with MMU
notifier in this series.

A GUP that can't sleep can't pagefault which makes it a really weird
pattern

get_user_pages/get_user_pages_fast must not be called under a spinlock.
We have the somewhat misnamed __get_user_page_fast that just does a
lookup for existing pages and never faults for a few places that need
to do that lookup from contexts where we can't sleep.

Yes, I do use __get_user_pages_fast() in the code.

Thanks