Re: [patch V2 1/2] mm: swap: Provide lru_add_drain_all_cpuslocked()

[Michal Hocko]

On Tue 04-07-17 14:48:56, Thomas Gleixner wrote:
> On Tue, 4 Jul 2017, Michal Hocko wrote:
> > On Tue 04-07-17 11:32:33, Thomas Gleixner wrote:
> > > The rework of the cpu hotplug locking unearthed potential deadlocks with
> > > the memory hotplug locking code.
> > > 
> > > The solution for these is to rework the memory hotplug locking code as well
> > > and take the cpu hotplug lock before the memory hotplug lock in
> > > mem_hotplug_begin(), but this will cause a recursive locking of the cpu
> > > hotplug lock when the memory hotplug code calls lru_add_drain_all().
> > > 
> > > Split out the inner workings of lru_add_drain_all() into
> > > lru_add_drain_all_cpuslocked() so this function can be invoked from the
> > > memory hotplug code with the cpu hotplug lock held.
> > 
> > You have added callers in the later patch in the series AFAICS which
> > is OK but I think it would be better to have them in this patch
> > already. Nothing earth shattering (maybe a rebase artifact).
> 
> The requirement for changing that comes with the extra hotplug locking in
> mem_hotplug_begin(). That is required to establish the proper lock order
> and then causes the recursive locking in the next patch. Adding the caller
> here would be wrong, because then lru_add_drain_all_cpuslocked() would be
> called unprotected. Hens and eggs as usual :)

Yeah, you are right. My bad I should have noticed that.
-- 
Michal Hocko
SUSE Labs