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SubjectRe: [PATCH v2 1/1] mm/vmscan.c: Prevent allocating shrinker_info on offlined nodes
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On 12/7/21 19:26, Yang Shi wrote:
> On Tue, Dec 7, 2021 at 3:44 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>>
>> On Tue, 7 Dec 2021 17:40:13 -0500 Nico Pache <npache@redhat.com> 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@dhcp22.suse.cz/T/#u
>
> 2. What this patch does. Proposed originally from
> https://lore.kernel.org/all/20211108202325.20304-1-amakhalov@vmware.com/T/#u

Correct me if im wrong, but isn't that a different caller? This patch fixes the
issue in expand_one_shrinker_info.

> 3. From David, fix in node_zonelist().
> https://lore.kernel.org/all/51c65635-1dae-6ba4-daf9-db9df0ec35d8@redhat.com/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?
>

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