Re: [PATCH] mm/hugetlb: fix memory offline failure due to hwpoisoned file hugetlb

[Jinjiang Tu <tujinjiang@huawei.com>]

在 2026/3/20 10:34, Miaohe Lin 写道:
> On 2026/3/18 10:07, Jinjiang Tu wrote:
>> When a file hugetlb folio triggers UCE, me_huge_page() will keep the
>> hugetlb folio in pagcahe with refcount increased and PG_hwpoison set. Even
>> after the hugetlb file is deleted, the hugetlb folio is still leaked.
>>
>> If we want to offline the memory block that the hwpoisoned hugetlb folio
>> belongs to, it fails in dissolve_free_hugetlb_folios() due to the
>> hwpoisoned hugetlb folio isn't free.
>>
>> I can reproduce this issue with the following steps in qemu:
>>   1) echo offline >/sys/devices/system/memory/auto_online_blocks
>>   2) in qemu monitor:
>>         object_add memory-backend-ram,id=mem10,size=1G
>>         device_add pc-dimm,id=dimm1,memdev=mem10,node=2
>>   3) echo online_movable > /sys/devices/system/node/node2/memory136/state
>>   4) echo 5 > /sys/devices/system/node/node2/hugepages/hugepages-2048kB/nr_hugepages
>>   5) run ./hugetlb_file. This process will receive SIGBUS.
>>   6) remove the hugetlbfs file.
>>   7) echo offline > /sys/devices/system/node/node2/memory136/state
>>
>> hugetlb_file.c:
>>    fd = open("/dev/hugepages/my_hugepage_file", O_CREAT | O_RDWR, 0755);
>>    fallocate(fd, 0, 0, HUGEPAGE_SIZE * 2);
>>    addr = mmap(NULL, HUGEPAGE_SIZE * 2, PROT_READ | PROT_WRITE,
>> 		MAP_SHARED | MAP_HUGETLB, fd, 0);
>>    memset(addr, 0xaa, HUGEPAGE_SIZE * 2);
>>    madvise(addr, HUGEPAGE_SIZE, MADV_HWPOISON);
>>
>> To fix it, when deleting hugetlb folio from pagecache, mark the hugetlb
>> folio temporary, and put the refcount increased by memory-failure. After
>> the hugetlb folio is deleted from pagecache, the refcount is decreased to
>> zero and the hugetlb folio is dissolved.
> Thanks for your patch.
>
>> Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>
>> ---
>>   fs/hugetlbfs/inode.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
>> index 3f70c47981de..6bebe2e67f3e 100644
>> --- a/fs/hugetlbfs/inode.c
>> +++ b/fs/hugetlbfs/inode.c
>> @@ -603,6 +603,11 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
>>   							index, truncate_op))
>>   				freed++;
>>   
>> +			if (unlikely(folio_test_hwpoison(folio))) {
>> +				folio_set_hugetlb_temporary(folio);
> I think it is not needed to mark the hugetlb folio as temporary because
> offline_pages() will call dissolve_free_hugetlb_folios().

Indeed. I was intended to avoid this hugetlb allocated again, but
dequeue_hugetlb_folio_node_exact() will check PG_hwpoison.

>
>> +				folio_put(folio);
> __get_huge_page_for_hwpoison() will always set hwpoison for hugetlb folio
> even without page refcnt increased. So this folio_put() might be unexpected.
> Please see [1] for detail.

When memory-failure races with migration, __get_huge_page_for_hwpoison()
will set hwpoison without page refcnt increased. In common case, ref is
increased before setting hwpoison.

> Thanks.
> .