Re: [RFC PATCH] mm: thp: grab the lock before manipulation defer list

[Michal Hocko]

On Tue 07-01-20 09:22:41, Wei Yang wrote:
> On Mon, Jan 06, 2020 at 11:23:45AM +0100, Michal Hocko wrote:
> >On Fri 03-01-20 22:34:07, Wei Yang wrote:
> >> As all the other places, we grab the lock before manipulate the defer list.
> >> Current implementation may face a race condition.
> >
> >Please always make sure to describe the effect of the change. Why a racy
> >list_empty check matters?
> >
> 
> Hmm... access the list without proper lock leads to many bad behaviors.

My point is that the changelog should describe that bad behavior.

> For example, if we grab the lock after checking list_empty, the page may
> already be removed from list in split_huge_page_list. And then list_del_init
> would trigger bug.

And how does list_empty check under the lock guarantee that the page is
on the deferred list?
-- 
Michal Hocko
SUSE Labs