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.
> @@ -4879,7 +4887,6 @@ static ssize_t show_slab_objects(struct kmem_cache *s,
> x += sprintf(buf + x, " N%d=%lu",
> node, nodes[node]);
> #endif
> - put_online_mems();
> kfree(nodes);
> return x + sprintf(buf + x, "\n");
> }
