Messages in this thread | | | Subject | Re: [PATCH] mm: fix invalid node in alloc_migrate_target() | From | Vlastimil Babka <> | Date | Tue, 29 Mar 2016 12:06:10 +0200 |
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On 03/29/2016 11:52 AM, Vlastimil Babka wrote: > On 03/26/2016 06:31 AM, Xishi Qiu wrote: >> On 2016/3/26 3:22, Andrew Morton wrote: >> >>> On Fri, 25 Mar 2016 14:56:04 +0800 Xishi Qiu <qiuxishi@huawei.com> wrote: >>> >>>> It is incorrect to use next_node to find a target node, it will >>>> return MAX_NUMNODES or invalid node. This will lead to crash in >>>> buddy system allocation. >>>> >>>> ... >>>> >>>> --- a/mm/page_isolation.c >>>> +++ b/mm/page_isolation.c >>>> @@ -289,11 +289,11 @@ struct page *alloc_migrate_target(struct page *page, unsigned long private, >>>> * now as a simple work-around, we use the next node for destination. >>>> */ >>>> if (PageHuge(page)) { >>>> - nodemask_t src = nodemask_of_node(page_to_nid(page)); >>>> - nodemask_t dst; >>>> - nodes_complement(dst, src); >>>> + int node = next_online_node(page_to_nid(page)); >>>> + if (node == MAX_NUMNODES) >>>> + node = first_online_node; >>>> return alloc_huge_page_node(page_hstate(compound_head(page)), >>>> - next_node(page_to_nid(page), dst)); >>>> + node); >>>> } >>>> >>>> if (PageHighMem(page)) >>> >>> Indeed. Can you tell us more about this circumstances under which the >>> kernel will crash? I need to decide which kernel version(s) need the >>> patch, but the changelog doesn't contain the info needed to make this >>> decision (it should). >>> >> >> Hi Andrew, >> >> I read the code v4.4, and find the following path maybe trigger the bug. >> >> alloc_migrate_target() >> alloc_huge_page_node() // the node may be offline or MAX_NUMNODES >> __alloc_buddy_huge_page_no_mpol() >> __alloc_buddy_huge_page() >> __hugetlb_alloc_buddy_huge_page() > > The code in this functions seems to come from 099730d67417d ("mm, > hugetlb: use memory policy when available") by Dave Hansen (adding to > CC), which was indeed merged in 4.4-rc1. > > However, alloc_pages_node() is only called in the block guarded by: > > if (!IS_ENABLED(CONFIG_NUMA) || !vma) { > > The rather weird "!IS_ENABLED(CONFIG_NUMA)" part comes from immediate > followup commit e0ec90ee7e6f ("mm, hugetlbfs: optimize when NUMA=n") > > So I doubt the code path here can actually happen. But it's fragile and > confusing nevertheless.
Ah, so there's actually a dangerous path: alloc_huge_page_node() dequeue_huge_page_node() list_for_each_entry(page, &h->hugepage_freelists[nid], lru)
hugepage_freelists is MAX_NUMNODES sized, so when nid is MAX_NUMNODES, we access past it.
However, look closer at how nid is obtained in alloc_migrate_target():
nodemask_t src = nodemask_of_node(page_to_nid(page)); nodemask_t dst; nodes_complement(dst, src);
nid = next_node(page_to_nid(page), dst)
for nid to be MAX_NUMNODES, the original page has to be on node MAX_NUMNODES-1, otherwise the complement part means we hit the very next bit which is set.
It's actually a rather obfuscated way of doing:
nid = page_to_nid(page) + 1;
In that case the problem is in commit c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to handle hugepage") from 3.12 and will likely affect only people that tune down MAX_NUMNODES to match their machine.
>> alloc_pages_node() >> __alloc_pages_node() >> VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES); >> VM_WARN_ON(!node_online(nid)); >> >> Thanks, >> Xishi Qiu >> >
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