Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()

Qian Cai
2019-10-10T13:12:02Z

On Thu, 2019-10-10 at 12:59 +0200, Michal Hocko wrote:
> On Thu 10-10-19 05:01:44, Qian Cai wrote:
> >
> >
> > > On Oct 9, 2019, at 12:23 PM, Michal Hocko <mhocko@kernel.org> wrote:
> > >
> > > If this was only about the memory offline code then I would agree. But
> > > we are talking about any printk from the zone->lock context and that is
> > > a bigger deal. Besides that it is quite natural that the printk code
> > > should be more universal and allow to be also called from the MM
> > > contexts as much as possible. If there is any really strong reason this
> > > is not possible then it should be documented at least.
> >
> > Where is the best place to document this? I am thinking about under
> > the “struct zone” definition’s lock field in mmzone.h.
>
> I am not sure TBH and I do not think we have reached the state where
> this would be the only way forward.

How about I revised the changelog to focus on memory offline rather than making
a rule that nobody should call printk() with zone->lock held?