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Message-ID: <c97dedf5-0f45-5082-64b6-ef0772dc33a3@huawei.com>
Date: Tue, 30 Sep 2025 14:31:36 +0800
From: Miaohe Lin <linmiaohe@...wei.com>
To: <jane.chu@...cle.com>
CC: David Hildenbrand <david@...hat.com>, Luis Chamberlain
<mcgrof@...nel.org>, syzbot
<syzbot+e6367ea2fdab6ed46056@...kaller.appspotmail.com>,
<akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>,
<linux-mm@...ck.org>, <nao.horiguchi@...il.com>,
<syzkaller-bugs@...glegroups.com>, "Pankaj Raghav (Samsung)"
<kernel@...kajraghav.com>, Zi Yan <ziy@...dia.com>
Subject: Re: [syzbot] [mm?] WARNING in memory_failure
On 2025/9/30 12:35, jane.chu@...cle.com wrote:
>
>
> On 9/29/2025 7:51 PM, Miaohe Lin wrote:
>> On 2025/9/30 2:23, jane.chu@...cle.com wrote:
>>>
>>>
>>> On 9/29/2025 10:49 AM, jane.chu@...cle.com wrote:
>>>>
>>>> On 9/29/2025 10:29 AM, jane.chu@...cle.com wrote:
>>>>>
>>>>> On 9/29/2025 4:08 AM, Pankaj Raghav (Samsung) wrote:
>>>>>>>
>>>>>>> I want to change all the split functions in huge_mm.h and provide
>>>>>>> mapping_min_folio_order() to try_folio_split() in truncate_inode_partial_folio().
>>>>>>>
>>>>>>> Something like below:
>>>>>>>
>>>>>>> 1. no split function will change the given order;
>>>>>>> 2. __folio_split() will no longer give VM_WARN_ONCE when provided new_order
>>>>>>> is smaller than mapping_min_folio_order().
>>>>>>>
>>>>>>> In this way, for an LBS folio that cannot be split to order 0, split
>>>>>>> functions will return -EINVAL to tell caller that the folio cannot
>>>>>>> be split. The caller is supposed to handle the split failure.
>>>>>>
>>>>>> IIUC, we will remove warn on once but just return -EINVAL in __folio_split()
>>>>>> function if new_order < min_order like this:
>>>>>> ...
>>>>>> min_order = mapping_min_folio_order(folio->mapping);
>>>>>> if (new_order < min_order) {
>>>>>> - VM_WARN_ONCE(1, "Cannot split mapped folio below min- order: %u",
>>>>>> - min_order);
>>>>>> ret = -EINVAL;
>>>>>> goto out;
>>>>>> }
>>>>>> ...
>>>>>
>>>>> Then the user process will get a SIGBUS indicting the entire huge page at higher order -
>>>>> folio_set_has_hwpoisoned(folio);
>>>>> if (try_to_split_thp_page(p, false) < 0) {
>>>>> res = -EHWPOISON;
>>>>> kill_procs_now(p, pfn, flags, folio);
>>>>> put_page(p);
>>>>> action_result(pfn, MF_MSG_UNSPLIT_THP, MF_FAILED);
>>>>> goto unlock_mutex;
>>>>> }
>>>>> VM_BUG_ON_PAGE(!page_count(p), p);
>>>>> folio = page_folio(p);
>>>>>
>>>>> the huge page is not usable any way, kind of similar to the hugetlb page situation: since the page cannot be splitted, the entire page is marked unusable.
>>>>>
>>>>> How about keep the current huge page split code as is, but change the M- F code to recognize that in a successful splitting case, the poisoned page might just be in a lower folio order, and thus, deliver the SIGBUS ?
>>>>>
>>>>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>>>>> index a24806bb8e82..342c81edcdd9 100644
>>>>> --- a/mm/memory-failure.c
>>>>> +++ b/mm/memory-failure.c
>>>>> @@ -2291,7 +2291,9 @@ int memory_failure(unsigned long pfn, int flags)
>>>>> * page is a valid handlable page.
>>>>> */
>>>>> folio_set_has_hwpoisoned(folio);
>>>>> - if (try_to_split_thp_page(p, false) < 0) {
>>>>> + ret = try_to_split_thp_page(p, false);
>>>>> + folio = page_folio(p);
>>>>> + if (ret < 0 || folio_test_large(folio)) {
>>>>> res = -EHWPOISON;
>>>>> kill_procs_now(p, pfn, flags, folio);
>>>>> put_page(p);
>>>>> @@ -2299,7 +2301,6 @@ int memory_failure(unsigned long pfn, int flags)
>>>>> goto unlock_mutex;
>>>>> }
>>>>> VM_BUG_ON_PAGE(!page_count(p), p);
>>>>> - folio = page_folio(p);
>>>>> }
>>>>>
>>>>> thanks,
>>>>> -jane
>>>>
>>>> Maybe this is better, in case there are other reason for split_huge_page() to return -EINVAL.
>>>>
>>>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>>>> index a24806bb8e82..2bfa05acae65 100644
>>>> --- a/mm/memory-failure.c
>>>> +++ b/mm/memory-failure.c
>>>> @@ -1659,9 +1659,10 @@ static int identify_page_state(unsigned long pfn, struct page *p,
>>>> static int try_to_split_thp_page(struct page *page, bool release)
>>>> {
>>>> int ret;
>>>> + int new_order = min_order_for_split(page_folio(page));
>>>>
>>>> lock_page(page);
>>>> - ret = split_huge_page(page);
>>>> + ret = split_huge_page_to_list_to_order(page, NULL, new_order);
>>>> unlock_page(page);
>>>>
>>>> if (ret && release)
>>>> @@ -2277,6 +2278,7 @@ int memory_failure(unsigned long pfn, int flags)
>>>> folio_unlock(folio);
>>>>
>>>> if (folio_test_large(folio)) {
>>>> + int ret;
>>>> /*
>>>> * The flag must be set after the refcount is bumped
>>>> * otherwise it may race with THP split.
>>>> @@ -2291,7 +2293,9 @@ int memory_failure(unsigned long pfn, int flags)
>>>> * page is a valid handlable page.
>>>> */
>>>> folio_set_has_hwpoisoned(folio);
>>>> - if (try_to_split_thp_page(p, false) < 0) {
>>>> + ret = try_to_split_thp_page(p, false);
>>>> + folio = page_folio(p);
>>>> + if (ret < 0 || folio_test_large(folio)) {
>>>> res = -EHWPOISON;
>>>> kill_procs_now(p, pfn, flags, folio);
>>>> put_page(p);
>>>> @@ -2299,7 +2303,6 @@ int memory_failure(unsigned long pfn, int flags)
>>>> goto unlock_mutex;
>>>> }
>>>> VM_BUG_ON_PAGE(!page_count(p), p);
>>>> - folio = page_folio(p);
>>>> }
>>>>
>>>> /*
>>>> @@ -2618,7 +2621,8 @@ static int soft_offline_in_use_page(struct page *page)
>>>> };
>>>>
>>>> if (!huge && folio_test_large(folio)) {
>>>> - if (try_to_split_thp_page(page, true)) {
>>>> + if ((try_to_split_thp_page(page, true)) ||
>>>> + folio_test_large(page_folio(page))) {
>>>> pr_info("%#lx: thp split failed\n", pfn);
>>>> return -EBUSY;
>>>> }
>>>
>>> In soft offline, better to check if (min_order_for_split > 0), no need to split, just return for now ...
>>
>> I might be miss something but why we have to split it? Could we migrate the whole thp or folio with min_order instead?
>
> The soft offline code was originally written with the assumption that only 1 base page will be offlined.
Yes, only page corresponding to parameter @pfn of soft_offline_page() will be offlined.
>
> With the recent introduction of min_order, it might quietly offline multiple pages, is that a desirable thing?
I don't think so. Even if try_to_split_thp_page splits folio into smaller one with min_order, page_handle_poison()
will put back the folio into buddy after migrate_pages, set the hwpoisoned flag to raw error page and hold the extra
refcnt. So only raw error page will be offlined while other sub-pages will be put back into buddy.
Or am I miss something?
Thanks.
.
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