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Message-ID: <CAHbLzkoCds-WOoN5CKas4DThk8hU65pgtMcga10QEqEmKU2f5A@mail.gmail.com>
Date: Tue, 7 Dec 2021 16:26:28 -0800
From: Yang Shi <shy828301@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Nico Pache <npache@...hat.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux MM <linux-mm@...ck.org>,
Shakeel Butt <shakeelb@...gle.com>,
Kirill Tkhai <ktkhai@...tuozzo.com>,
Roman Gushchin <guro@...com>, Vlastimil Babka <vbabka@...e.cz>,
Vladimir Davydov <vdavydov.dev@...il.com>, raquini@...hat.com,
Michal Hocko <mhocko@...e.com>,
David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH v2 1/1] mm/vmscan.c: Prevent allocating shrinker_info on
offlined nodes
On Tue, Dec 7, 2021 at 3:44 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Tue, 7 Dec 2021 17:40:13 -0500 Nico Pache <npache@...hat.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
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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