On Fri, Aug 30, 2019 at 05:40:23PM +0200, Jan Kara wrote:

Are the page dereferences above safe? I suppose lock_page_memcg() protects
the page->mem_cgroup->css.cgroup->kn->id dereference? But page->mapping
does not seem to be protected by page lock?

Forgot to respond to the mem_cgroup part.  The page to memcg
association never changes on cgroup2 as long as the page has ref, so I
think that one should be safe.

Thanks.

-- 
tejun