linux-kernel - Re: [PATCH v3 5/5] mm/memory-failure: send SIGBUS in the event of thp split fail

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Date: Thu, 23 May 2024 13:01:50 -0700
From: Jane Chu <jane.chu@...cle.com>
To: Miaohe Lin <linmiaohe@...wei.com>, nao.horiguchi@...il.com,
        akpm@...ux-foundation.org, osalvador@...e.de, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 5/5] mm/memory-failure: send SIGBUS in the event of thp
 split fail

On 5/22/2024 8:02 PM, Miaohe Lin wrote:

> On 2024/5/22 7:54, Jane Chu wrote:
>> While handling hwpoison in a THP page, it is possible that
>> try_to_split_thp_page() fails. For example, when the THP page has
>> been RDMA pinned. At this point, the kernel cannot isolate the
>> poisoned THP page, all it could do is to send a SIGBUS to the user
>> process with meaningful payload to give user-level recovery a chance.
>>
> Thanks for your patch.
>
>> Signed-off-by: Jane Chu <jane.chu@...cle.com>
>> ---
>>   mm/memory-failure.c | 35 ++++++++++++++++++++++++++++++-----
>>   1 file changed, 30 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>> index 794196951a04..a14d56e66902 100644
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -1706,7 +1706,12 @@ static int identify_page_state(unsigned long pfn, struct page *p,
>>   	return page_action(ps, p, pfn);
>>   }
>>   
>> -static int try_to_split_thp_page(struct page *page)
>> +/*
>> + * When 'release' is 'false', it means that if thp split has failed,
>> + * there is still more to do, hence the page refcount we took earlier
>> + * is still needed.
>> + */
>> +static int try_to_split_thp_page(struct page *page, bool release)
>>   {
>>   	int ret;
>>   
>> @@ -1714,7 +1719,7 @@ static int try_to_split_thp_page(struct page *page)
>>   	ret = split_huge_page(page);
>>   	unlock_page(page);
>>   
>> -	if (unlikely(ret))
>> +	if (ret && release)
>>   		put_page(page);
> Is "unlikely" still needed?
I'd say not, because this code is not on performance sensitive code path.
>>   
>>   	return ret;
>> @@ -2187,6 +2192,24 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
>>   	return rc;
>>   }
>>   
>> +/*
>> + * The calling condition is as such: thp split failed, page might have
>> + * been RDMA pinned, not much can be done for recovery.
>> + * But a SIGBUS should be delivered with vaddr provided so that the user
>> + * application has a chance to recover. Also, application processes'
>> + * election for MCE early killed will be honored.
>> + */
>> +static int kill_procs_now(struct page *p, unsigned long pfn, int flags,
>> +				struct folio *folio)
>> +{
>> +	LIST_HEAD(tokill);
>> +
>> +	collect_procs(folio, p, &tokill, flags & MF_ACTION_REQUIRED);
>> +	kill_procs(&tokill, true, pfn, flags);
>> +
>> +	return -EHWPOISON;
>> +}
>> +
>>   /**
>>    * memory_failure - Handle memory failure of a page.
>>    * @pfn: Page Number of the corrupted page
>> @@ -2328,8 +2351,10 @@ 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) < 0) {
>> -			res = action_result(pfn, MF_MSG_UNSPLIT_THP, MF_IGNORED);
>> +		if (try_to_split_thp_page(p, false) < 0) {
>> +			res = kill_procs_now(p, pfn, flags, folio);
> No strong opinion but we might remove the return value of kill_procs_now as
> it always return -EHWPOISON? We could simply set res to -EHWPOISON here.
I like that, will change.
>
> Besides from above possible nits, this patch looks good to me.
> Acked-by: Miaohe Lin <linmiaohe@...wei.com>
> Thanks.

Thank!

-jane

> .
>