On Thu, 3 Oct 2019, Qian Cai wrote:
> > > diff --git a/mm/slub.c b/mm/slub.c
> > > index 42c1b3af3c98..922cdcf5758a 100644
> > > --- a/mm/slub.c
> > > +++ b/mm/slub.c
> > > @@ -4838,7 +4838,15 @@ static ssize_t show_slab_objects(struct kmem_cache *s,
> > > }
> > > }
> > >
> > > - get_online_mems();
> > > +/*
> > > + * It is not possible to take "mem_hotplug_lock" here, as it has already held
> > > + * "kernfs_mutex" which could race with the lock order:
> > > + *
> > > + * mem_hotplug_lock->slab_mutex->kernfs_mutex
> > > + *
> > > + * In the worest case, it might be mis-calculated while doing NUMA node
> > > + * hotplug, but it shall be corrected by later reads of the same files.
> > > + */
> > > #ifdef CONFIG_SLUB_DEBUG
> > > if (flags & SO_ALL) {
> > > struct kmem_cache_node *n;
> >
> > No objection to removing the {get,put}_online_mems() but the comment
> > doesn't match the kernel style. I actually don't think we need the
> > comment at all, actually.
>
> I am a bit worry about later someone comes to add the lock back as he/she
> figures out that it could get more accurate statistics that way, but I agree it
> is probably an overkill.
>
Maybe just a small comment that follows the kernel coding style?
