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[2003:d8:2f1a:f500:4346:f17c:2bde:808c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-454cd4f398csm11291735e9.2.2025.07.08.02.54.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Jul 2025 02:54:42 -0700 (PDT) Message-ID: <8c9719f0-c072-40bb-b7f6-6f2cc41a31dc@redhat.com> Date: Tue, 8 Jul 2025 11:54:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] mm/memory_hotplug: fix hwpoisoned large folio handling in do_migrate_range To: Jinjiang Tu , Oscar Salvador Cc: akpm@linux-foundation.org, linmiaohe@huawei.com, mhocko@kernel.org, linux-mm@kvack.org, wangkefeng.wang@huawei.com, Zi Yan References: <20250627125747.3094074-1-tujinjiang@huawei.com> <20250627125747.3094074-3-tujinjiang@huawei.com> <373d02c5-2b62-8543-b786-8fd591ad56eb@huawei.com> <61325284-d1d6-a973-8aa7-c0f226db95fa@huawei.com> <7b2c054b-fc33-4127-aaa9-9edf6a63e142@redhat.com> <924d9d25-e53c-f159-6ec0-e1fd4e96d6e2@huawei.com> <4c5d4fd5-5582-11d8-9fee-24828ac1913d@huawei.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: k9zzw13jnsy4owocrtkytdms6yh58d8k X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 2015740007 X-HE-Tag: 1751968486-962182 X-HE-Meta: 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 dMMm2FXr 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 08.07.25 03:15, Jinjiang Tu wrote: > > 在 2025/7/7 20:37, David Hildenbrand 写道: >> On 07.07.25 13:51, Jinjiang Tu wrote: >>> >>> 在 2025/7/3 17:06, David Hildenbrand 写道: >>>> On 03.07.25 10:24, Jinjiang Tu wrote: >>>>> >>>>> 在 2025/7/3 15:57, David Hildenbrand 写道: >>>>>> On 03.07.25 09:46, Jinjiang Tu wrote: >>>>>>> >>>>>>> 在 2025/7/1 22:21, Oscar Salvador 写道: >>>>>>>> On Fri, Jun 27, 2025 at 08:57:47PM +0800, Jinjiang Tu wrote: >>>>>>>>> In do_migrate_range(), the hwpoisoned folio may be large folio, >>>>>>>>> which >>>>>>>>> can't be handled by unmap_poisoned_folio(). >>>>>>>>> >>>>>>>>> I can reproduce this issue in qemu after adding delay in >>>>>>>>> memory_failure() >>>>>>>>> >>>>>>>>> BUG: kernel NULL pointer dereference, address: 0000000000000000 >>>>>>>>> Workqueue: kacpi_hotplug acpi_hotplug_work_fn >>>>>>>>> RIP: 0010:try_to_unmap_one+0x16a/0xfc0 >>>>>>>>>      >>>>>>>>>      rmap_walk_anon+0xda/0x1f0 >>>>>>>>>      try_to_unmap+0x78/0x80 >>>>>>>>>      ? __pfx_try_to_unmap_one+0x10/0x10 >>>>>>>>>      ? __pfx_folio_not_mapped+0x10/0x10 >>>>>>>>>      ? __pfx_folio_lock_anon_vma_read+0x10/0x10 >>>>>>>>>      unmap_poisoned_folio+0x60/0x140 >>>>>>>>>      do_migrate_range+0x4d1/0x600 >>>>>>>>>      ? slab_memory_callback+0x6a/0x190 >>>>>>>>>      ? notifier_call_chain+0x56/0xb0 >>>>>>>>>      offline_pages+0x3e6/0x460 >>>>>>>>>      memory_subsys_offline+0x130/0x1f0 >>>>>>>>>      device_offline+0xba/0x110 >>>>>>>>>      acpi_bus_offline+0xb7/0x130 >>>>>>>>>      acpi_scan_hot_remove+0x77/0x290 >>>>>>>>>      acpi_device_hotplug+0x1e0/0x240 >>>>>>>>>      acpi_hotplug_work_fn+0x1a/0x30 >>>>>>>>>      process_one_work+0x186/0x340 >>>>>>>>> >>>>>>>>> In this case, just make offline_pages() fail. >>>>>>>>> >>>>>>>>> Besides, do_migrate_range() may be called between >>>>>>>>> memory_failure set >>>>>>>>> hwposion flag and ioslate the folio from lru, so remove WARN_ON(). >>>>>>>>> In other >>>>>>>>> places, unmap_poisoned_folio() is called when the folio is >>>>>>>>> isolated, obey >>>>>>>>> it in do_migrate_range() too. >>>>>>>>> >>>>>>>>> Fixes: b15c87263a69 ("hwpoison, memory_hotplug: allow hwpoisoned >>>>>>>>> pages to be offlined") >>>>>>>>> Signed-off-by: Jinjiang Tu >>>>>>>> ... >>>>>>>>> @@ -2041,11 +2048,9 @@ int offline_pages(unsigned long start_pfn, >>>>>>>>> unsigned long nr_pages, >>>>>>>>>                     ret = scan_movable_pages(pfn, end_pfn, &pfn); >>>>>>>>>                  if (!ret) { >>>>>>>>> -                /* >>>>>>>>> -                 * TODO: fatal migration failures should bail >>>>>>>>> -                 * out >>>>>>>>> -                 */ >>>>>>>>> -                do_migrate_range(pfn, end_pfn); >>>>>>>>> +                ret = do_migrate_range(pfn, end_pfn); >>>>>>>>> +                if (ret) >>>>>>>>> +                    break; >>>>>>>> I am not really sure about this one. >>>>>>>> I get the reason you're adding it, but note that migrate_pages() >>>>>>>> can >>>>>>>> also return >>>>>>>> "fatal" errors and we don't propagate that. >>>>>>>> >>>>>>>> The moto has always been to migrate as much as possible, and this >>>>>>>> changes this >>>>>>>> behaviour. >>>>>>> If we just skip to next pfn, offline_pages() will deadloop >>>>>>> meaningless >>>>>>> util received signal. >>>>>> >>>>>> Yeah, that's also not good, >>>>>> >>>>>>> It seems there is no document to guarantee memory offline have to >>>>>>> migrate as much as possible. >>>>>> >>>>>> We should try offlining as good as possible. But if there is >>>>>> something >>>>>> we just cannot possibly migrate, there is no sense in retrying. >>>>>> >>>>>> Now, could we run into this case here because we are racing with >>>>>> other >>>>>> code, and actually retrying again could make it work? >>>>>> >>>>>> Remind me again: how exactly do we arrive at this point of having a >>>>>> large folio that is hwpoisoned but still mapped? >>>>>> >>>>>> In memory_failure(), we do on a  large folio >>>>>> >>>>>> 1) folio_set_has_hwpoisoned >>>>>> 2) try_to_split_thp_page >>>>>> 3) if splitting fails, kill_procs_now >>>>> If 2) is executed when do_migrate_range() increment the refcount of >>>>> the >>>>> folio, the split fails, and retry is meaningless. >>>> >>>> kill_procs_now will kill all processes, effectively unmapping the >>>> folio in that case? >>>> >>>> So retrying would later just ... get us an unmapped folio and we can >>>> make progress? >>>> >>> kill_procs_now()->collect_procs() collects the tasks to kill. But not >>> all tasks that maps the folio >>> will be collected, >>> collect_procs_anon()->task_early_kill()->find_early_kill_thread() >>> will not >>> select the task (not current) if PF_MCE_PROCESS isn't set and >>> sysctl_memory_failure_early_kill >>> isn't enabled (this is the default behaviour). >> >> I think you're right, that's rather nasty. >> >> We fail to split, but keep the folio mapped into some processes. >> >> And we can't unmap it because unmap_poisoned_folio() does not properly >> support large folios yet. >> >> We really should unmap the folio when splitting fail. :( > unmap_poisoned_folio() doesn't guarantee the folio is unmapped > successfully, according > to the return val. Although I don't know in which case we will fail to > unmap. I think there are only cases for anon folios, when the folio is in the swapcache or it's lazyfree (!swapbacked) and we run into the walk_abort cases. Retrying will likely make it work in many cases I assume. This is all really rather suboptimal and, I'm afraid, requires much bigger rework to improve it. Failing memory offlining is also not nice. I was wondering whether we can just keep splitting the folio until it works: diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index b1caedbade5b1..991b095ac7e78 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1819,6 +1819,19 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn) pfn = folio_pfn(folio) + folio_nr_pages(folio) - 1; if (folio_contain_hwpoisoned_page(folio)) { + /* + * unmap_poisoned_folio() cannot handle THPs, so + * keep trying to split first. + */ + if (folio_test_large(folio) && !folio_test_hugetlb(folio)) { + folio_lock(folio); + split_huge_page_to_list_to_order(&folio->page, + NULL, + min_order_for_split(folio)); + folio_unlock(folio); + if (folio_test_large(folio)) + goto put_folio; + } if (WARN_ON(folio_test_lru(folio))) folio_isolate_lru(folio); if (folio_mapped(folio)) { Probably the WARN_ON can indeed trigger now. @Zi Yan, on a related note ... in memory_failure(), we call try_to_split_thp_page(). If it works, we assume that we have a small folio. But that is not the case if split_huge_page() cannot split it to order-0 ... min_order_for_split(). I'm afraid we havbe more such code that does not expect that if split_huge_page() succeeds that we still have a large folio ... -- Cheers, David / dhildenb