On Tue, 7 Dec 2021 17:40:13 -0500 Nico Pache <npache@xxxxxxxxxx> wrote:
> We have run into a panic caused by a shrinker allocation being attempted
> on an offlined node.
>
> Our crash analysis has determined that the issue originates from trying
> to allocate pages on an offlined node in expand_one_shrinker_info. This
> function makes the incorrect assumption that we can allocate on any node.
> To correct this we make sure the node is online before tempting an
> allocation. If it is not online choose the closest node.
This isn't fully accurate, is it? We could allocate on a node which is
presently offline but which was previously onlined, by testing
NODE_DATA(nid).
It isn't entirely clear to me from the v1 discussion why this approach
isn't being taken?
AFAICT the proposed patch is *already* taking this approach, by having
no protection against a concurrent or subsequent node offlining?
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -222,13 +222,16 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
> int size = map_size + defer_size;
>
> for_each_node(nid) {
> + int tmp = nid;
Not `tmp', please. Better to use an identifier which explains the
variable's use. target_nid?
And a newline after defining locals, please.
> pn = memcg->nodeinfo[nid];
> old = shrinker_info_protected(memcg, nid);
> /* Not yet online memcg */
> if (!old)
> return 0;
>
> - new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, nid);
> + if(!node_online(nid))
s/if(/if (/
> + tmp = numa_mem_id();
> + new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, tmp);
> if (!new)
> return -ENOMEM;
>
And a code comment fully explaining what's going on here?
