Re: [PATCH v2] mm/hugetlb: fix memory offline failure due to hwpoisoned file hugetlb

[Jinjiang Tu <tujinjiang@huawei.com>]

在 2026/3/23 20:14, David Hildenbrand (Arm) 写道:
> On 3/21/26 03:10, 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, force to put ref of hwpoisoned hugetlb in memory offline, the
>> hwpoisoned hugetlb will be freed and succeeds to be dissolved. We couldn't
>> avoid races here, just like commit b023f46813cd ("memory-hotplug: skip
>> HWPoisoned page when offlining pages"), which force to skip hwpoisoned
>> page regardless of refcount.
> I always considered that handling quite dubious. Just because a page has
> hwpoisoned set doesn't mean that we can just offline it.
>
> I think that mus be cleaned up at some point.
>
> But not sure how to do this cleanly.
>
> Why do we even care about offlining memory with hwpoisoned pages? What
> is the use case for your change?

Considering CXL memory device and we hotplug the memory as NUMA. If the
device is disconnected, accessing the CXL memory will trigger memory-failure.

We still want to offline the memory, so that we can reonline and use the
memory again when CXL memory device is reconnected.

> I know, it's very desirable to do it, but I much rather have it not
> working then having something that is likely mostly broken and actually
> might cause harm.
>