On Tue, Dec 7, 2021 at 5:23 PM Yang Shi <shy828301@xxxxxxxxx> wrote: > > On Tue, Dec 7, 2021 at 4:33 PM Nico Pache <npache@xxxxxxxxxx> wrote: > > > > > > > > On 12/7/21 19:26, Yang Shi wrote: > > > On Tue, Dec 7, 2021 at 3:44 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > >> > > >> 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? > > > > > > AFAICT, we have not reached agreement on how to fix it yet. I saw 3 > > > proposals at least: > > > > > > 1. From Michal, allocate node data for all possible nodes. > > > https://lore.kernel.org/all/Ya89aqij6nMwJrIZ@xxxxxxxxxxxxxx/T/#u > > > > > > 2. What this patch does. Proposed originally from > > > https://lore.kernel.org/all/20211108202325.20304-1-amakhalov@xxxxxxxxxx/T/#u > > > > Correct me if im wrong, but isn't that a different caller? This patch fixes the > > issue in expand_one_shrinker_info. > > Yes, different caller, but same approach. The cons with this approach And the same underlying problem. > is we have to fix all the places. It seems Michal and David are not > fans for this approach IIRC. > > > > > > 3. From David, fix in node_zonelist(). > > > https://lore.kernel.org/all/51c65635-1dae-6ba4-daf9-db9df0ec35d8@xxxxxxxxxx/T/#u > > > > > >> > > >>> --- 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? > > > > >
