From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Alexey Makhalov <amakhalov@vmware.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"stable@vger.kernel.org" <stable@vger.kernel.org>,
Oscar Salvador <OSalvador@suse.com>
Subject: Re: [PATCH] mm: fix panic in __alloc_pages
Date: Tue, 2 Nov 2021 13:39:06 +0100 [thread overview]
Message-ID: <e7aed7c0-b7b1-4a94-f323-0bcde2f879d2@redhat.com> (raw)
In-Reply-To: <YYEun6s/mF9bE+rQ@dhcp22.suse.cz>
>> Yes, but a zonelist cannot be correct for an offline node, where we might
>> not even have an allocated pgdat yet. No pgdat, no zonelist. So as soon as
>> we allocate the pgdat and set the node online (->hotadd_new_pgdat()), the zone lists have to be correct. And I can spot an build_all_zonelists() in hotadd_new_pgdat().
>
> Yes, that is what I had in mind. We are talking about two things here.
> Memoryless nodes and offline nodes. The later sounds like a bug to me.
Agreed. memoryless nodes should just have proper zonelists -- which
seems to be the case.
>> Maybe __alloc_pages_bulk() and alloc_pages_node() should bail out directly
>> (VM_BUG()) in case we're providing an offline node with eventually no/stale pgdat as
>> preferred nid.
>
> Historically, those allocation interfaces were not trying to be robust
> against wrong inputs because that adds cpu cycles for everybody for
> "what if buggy" code. This has worked (surprisingly) well. Memory less
> nodes have brought in some confusion but this is still something that we
> can address on a higher level. Nobody give arbitrary nodes as an input.
> cpu_to_node might be tricky because it can point to a memory less node
> which along with __GFP_THISNODE is very likely not something anybody
> wants. Hence cpu_to_mem should be used for allocations. I hate we have
> two very similar APIs...
To be precise, I'm wondering if we should do:
diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 55b2ec1f965a..8c49b88336ee 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -565,7 +565,7 @@ static inline struct page *
__alloc_pages_node(int nid, gfp_t gfp_mask, unsigned int order)
{
VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES);
- VM_WARN_ON((gfp_mask & __GFP_THISNODE) && !node_online(nid));
+ VM_WARN_ON(!node_online(nid));
return __alloc_pages(gfp_mask, order, nid, NULL);
}
(Or maybe VM_BUG_ON)
Because it cannot possibly work and we'll dereference NULL later.
>
> But something seems wrong in this case. cpu_to_node shouldn't return
> offline nodes. That is just a land mine. It is not clear to me how the
> cpu has been brought up so that the numa node allocation was left
> behind. As pointed in other email add_cpu resp. cpu_up is not it.
> Is it possible that the cpu bring up was only half way?
I tried to follow the code (what sets a CPU present, what sets a CPU
online, when do we update cpu_to_node() mapping) and IMHO it's all a big
mess. Maybe it's clearer to people familiar with that code, but CPU
hotplug in general seems to be a confusing piece of (arch-specific) code.
Also, I have no clue if cpu_to_node() mapping will get invalidated after
unplugging that CPU, or if the mapping will simply stay around for all
eternity ...
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-11-02 12:39 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-01 20:13 [PATCH] mm: fix panic in __alloc_pages Alexey Makhalov
2021-11-01 20:38 ` Matthew Wilcox
2021-11-02 7:47 ` Michal Hocko
2021-11-02 8:12 ` David Hildenbrand
2021-11-02 8:48 ` Alexey Makhalov
2021-11-02 9:04 ` Michal Hocko
2021-11-02 9:24 ` David Hildenbrand
2021-11-02 10:34 ` Alexey Makhalov
2021-11-02 11:00 ` David Hildenbrand
2021-11-02 11:44 ` Michal Hocko
2021-11-02 12:06 ` David Hildenbrand
2021-11-02 12:27 ` Michal Hocko
2021-11-02 12:39 ` David Hildenbrand [this message]
2021-11-02 13:25 ` Michal Hocko
2021-11-02 13:41 ` David Hildenbrand
2021-11-02 14:12 ` Michal Hocko
2021-11-02 14:44 ` David Hildenbrand
2021-11-02 13:52 ` Oscar Salvador
2021-11-02 14:35 ` Michal Hocko
2021-11-08 6:12 ` Alexey Makhalov
2021-11-08 6:36 ` [PATCH v2] " Alexey Makhalov
2021-11-08 8:32 ` David Hildenbrand
2021-11-08 20:23 ` [PATCH v3] " Alexey Makhalov
2021-11-09 2:08 ` Eric Dumazet
2021-11-09 7:03 ` David Hildenbrand
2021-11-09 16:55 ` Eric Dumazet
2021-11-09 17:15 ` Michal Hocko
2021-11-09 19:06 ` Dennis Zhou
2021-11-09 19:54 ` Michal Hocko
2021-11-16 1:31 ` Alexey Makhalov
2021-11-16 9:17 ` Michal Hocko
2021-11-16 20:22 ` Alexey Makhalov
2021-11-18 8:35 ` Michal Hocko
2021-12-07 10:54 ` Michal Hocko
2021-12-07 11:08 ` David Hildenbrand
2021-12-07 12:13 ` Michal Hocko
2021-12-07 12:28 ` David Hildenbrand
2021-12-07 13:23 ` Michal Hocko
2021-12-07 15:09 ` David Hildenbrand
2021-12-07 15:29 ` Michal Hocko
2021-12-07 15:34 ` David Hildenbrand
2021-12-07 15:56 ` Michal Hocko
2021-12-07 16:09 ` David Hildenbrand
2021-12-07 16:27 ` Michal Hocko
2021-12-07 16:36 ` Michal Hocko
2021-12-07 16:40 ` David Hildenbrand
2021-12-08 8:28 ` Michal Hocko
2021-12-07 17:02 ` Alexey Makhalov
2021-12-07 17:13 ` David Hildenbrand
2021-12-07 17:17 ` Alexey Makhalov
2021-12-07 18:03 ` David Hildenbrand
2021-12-08 8:12 ` Michal Hocko
2021-12-08 8:24 ` David Hildenbrand
2021-12-08 8:34 ` Michal Hocko
2021-12-08 8:38 ` David Hildenbrand
2021-12-08 8:04 ` Michal Hocko
2021-12-08 8:19 ` Alexey Makhalov
2021-12-08 8:30 ` Michal Hocko
2021-12-08 8:54 ` Michal Hocko
2021-12-08 8:57 ` Alexey Makhalov
2021-12-08 9:55 ` Michal Hocko
2021-12-09 2:16 ` Alexey Makhalov
2021-12-09 8:46 ` Michal Hocko
2021-12-09 9:28 ` Alexey Makhalov
2021-12-09 9:56 ` Michal Hocko
2021-12-09 10:23 ` Alexey Makhalov
2021-12-09 13:29 ` Michal Hocko
2021-12-09 19:01 ` Alexey Makhalov
2021-12-10 9:11 ` Michal Hocko
2021-12-17 12:53 ` Michal Hocko
2021-12-21 5:46 ` Alexey Makhalov
2021-12-21 9:46 ` Michal Hocko
2021-12-21 20:23 ` Alexey Makhalov
2021-12-22 11:41 ` Michal Hocko
2021-12-09 10:48 ` Michal Hocko
2021-12-13 15:06 ` Michal Hocko
2021-12-13 15:07 ` David Hildenbrand
2021-12-14 8:38 ` Michal Hocko
2021-11-08 10:37 ` [PATCH v2] " Michal Hocko
2021-11-02 9:40 ` [PATCH] " Alexey Makhalov
2021-11-02 9:40 ` Michal Hocko
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