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Fri, 10 May 2024 10:59:39 +0800 Subject: Re: [PATCH 3/3] mm/memory-failure: send SIGBUS in the event of thp split fail To: Jane Chu , , , , References: <20240501232458.3919593-1-jane.chu@oracle.com> <20240501232458.3919593-4-jane.chu@oracle.com> <038cffc0-e027-b518-460f-40099819c588@huawei.com> <1b4c50b6-2371-4e1b-aef3-d70c32888054@oracle.com> <30d4d249-e3b1-79d5-3501-0ccb9c529110@huawei.com> <7a292357-8515-4ea6-b4d1-6ca6fa407e72@oracle.com> From: Miaohe Lin Message-ID: <32b88a87-8edc-12eb-1fd7-2a028b8f9fb3@huawei.com> Date: Fri, 10 May 2024 10:59:38 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <7a292357-8515-4ea6-b4d1-6ca6fa407e72@oracle.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.173.135.154] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To canpemm500002.china.huawei.com (7.192.104.244) X-Stat-Signature: ffm7a1g4jhwdota7fsoneyszumnmxby4 X-Rspamd-Queue-Id: B3C4914000A X-Rspamd-Server: rspam10 X-Rspam-User: X-HE-Tag: 1715309983-445766 X-HE-Meta: U2FsdGVkX18GfpfInMga7yQXrTHNyOqdYwYqPolPca0Hu0Wxid6h2RWbo0k1x3/xmgZ6GzA3dW8jVb19VC41Lb1d599ElfIHQerK8Puuo525aP2EarYbb2BzAxCIYCfri19eL6Y+Zq2r6aSefu82otKp9+tgb4wQMBVcBhZZckhGwOPEpkZC9PoTQBZj+zg5re8CBC7GSlALION/hvTDETuLil5C8hfJjoJJhX8Z2GarBD8DpROLzstWk9TgVQLKwoNW6fZqSEPNECR33QQXN2r3RKEQeukuPzitB5mfIiMxdZHrn7dJB3dNKcQ6tutp/5PBS8ujNbusEgDnZHxeczkvBksXcqTlXGHeYM1/s/85B2Nd0c8+ErfiTHhpOxCtssE2gmc7PRxII9TSsW67Vm1wLe3uC8HhSOH0DsvCz7mkBE3EKGQjxmr3iVFCB9pWeOFjVFyuDzsi73B5517qxpHNAYMI/T0+wMVEi+OnhV1UcshXWistb4lsXFfziZznUA/9LxGjc7+RKHvZ+X6guh+eBnFSkIaj/vTqft2gFX95SvLc88IwJL3VlfEIpvzKVGqbCJEqYnhGk1cFj4pn4oEIa8B7xY1ytJYn53YTYY8gTyT9w8vz5qZPJpZ3OPLxJKxN+gfeWt1mg4znTCKf1sVkUah+5Z3niu7YUV2MHIUKwRbESKnvZfRTtDx3/YGa0FPiHW7ScLOiFiJt9hT0S0jC0ucSn51DQoOQwAgwJA8zXM8crVK1NQ3V/Bh9mZwiVQ5PKM7BHbFGDKQGvJc8MoOwyfZoXBIeDB6zM6cJZMpUIqua4SHoI51kElVvtIugU1MEdf/UTNIMT7kOhK8dpDvePYf6N06Fx5O5pb6YdXOItIQXAGbpx36SUy0tD9NbRZwKmWXYBEhGtbHojzZNLfz3pQ3JKvxZWvaiVwz3hRfBNMlals6Z2+aq0K/ApPpxmXziT98TPNBi8GmflBi WdUYgTpn ndR/woKvDnGLJtA7psnY7nh9kxT9cIWZzRnxAxAAg+61XfeXXhYv9hXal1W07qyozNpZMvzsFb9pXCK+SMqEeY2Aj20MUr37BX3qtSAKwpd4++HjKpyxMR3Z8Xy29Vd3omQGPJTL6G1tZFlIyoIzmvakwXqkk5etNZDK5Le/OaEUBRB5upUCH9NsaA0XlcSl13DnBtaOezrgOUcXkN0H2AXIi2IKgUSY9qHh4arIvxMRCRK4PTG1PGV8MqA== 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 2024/5/9 23:34, Jane Chu wrote: > > On 5/9/2024 1:30 AM, Miaohe Lin wrote: >> On 2024/5/9 1:45, Jane Chu wrote: >>> On 5/8/2024 1:08 AM, Miaohe Lin wrote: >>> >>>> On 2024/5/7 4:26, Jane Chu wrote: >>>>> On 5/5/2024 12:00 AM, Miaohe Lin wrote: >>>>> >>>>>> On 2024/5/2 7:24, Jane Chu wrote: >>>>>>> When handle hwpoison in a GUP longterm pin'ed thp page, >>>>>>> try_to_split_thp_page() will fail. And at this point, there is little else >>>>>>> the kernel could do except sending a SIGBUS to the user process, thus >>>>>>> give it a chance to recover. >>>>>>> >>>>>>> Signed-off-by: Jane Chu >>>>>> Thanks for your patch. Some comments below. >>>>>> >>>>>>> --- >>>>>>>     mm/memory-failure.c | 36 ++++++++++++++++++++++++++++++++++++ >>>>>>>     1 file changed, 36 insertions(+) >>>>>>> >>>>>>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >>>>>>> index 7fcf182abb96..67f4d24a98e7 100644 >>>>>>> --- a/mm/memory-failure.c >>>>>>> +++ b/mm/memory-failure.c >>>>>>> @@ -2168,6 +2168,37 @@ 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 GUP longterm 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 page *hpage) >>>>>>> +{ >>>>>>> +    struct folio *folio = page_folio(hpage); >>>>>>> +    LIST_HEAD(tokill); >>>>>>> +    int res = -EHWPOISON; >>>>>>> + >>>>>>> +    /* deal with user pages only */ >>>>>>> +    if (PageReserved(p) || PageSlab(p) || PageTable(p) || PageOffline(p)) >>>>>>> +        res = -EBUSY; >>>>>>> +    if (!(PageLRU(hpage) || PageHuge(p))) >>>>>>> +        res = -EBUSY; >>>>>> Above checks seems unneeded. We already know it's thp? >>>>> Agreed. >>>>> >>>>> I  lifted these checks from hwpoison_user_mapping() with a hope to make kill_procs_now() more generic, >>>>> >>>>> such as, potentially replacing kill_accessing_processes() for re-accessing hwpoisoned page. >>>>> >>>>> But I backed out at last, due to concerns that my tests might not have covered sufficient number of scenarios. >>>>> >>>>>>> + >>>>>>> +    if (res == -EHWPOISON) { >>>>>>> +        collect_procs(folio, p, &tokill, flags & MF_ACTION_REQUIRED); >>>>>>> +        kill_procs(&tokill, true, pfn, flags); >>>>>>> +    } >>>>>>> + >>>>>>> +    if (flags & MF_COUNT_INCREASED) >>>>>>> +        put_page(p); >>>>>> This if block is broken. put_page() has been done when try_to_split_thp_page() fails? >>>>> put_page() has not been done if try_to_split_thp_page() fails, and I think it should. >>>> In try_to_split_thp_page(), if split_huge_page fails, i.e. ret != 0, put_page() is called. See below: >>>> >>>> static int try_to_split_thp_page(struct page *page) >>>> { >>>>      int ret; >>>> >>>>      lock_page(page); >>>>      ret = split_huge_page(page); >>>>      unlock_page(page); >>>> >>>>      if (unlikely(ret)) >>>>          put_page(page); >>>>      ^^^^^^^^^^^^^^^^^^^^^^^ >>>>      return ret; >>>> } >>>> >>>> Or am I miss something? >>> I think you caught a bug in my code, thanks! >>> >>> How about moving put_page() outside try_to_split_thp_page() ? >> If you want to send SIGBUS in the event of thp split fail, it might be required to do so. >> I think kill_procs_now() needs extra thp refcnt to do its work. > > Agreed.  I added an boolean to try_to_split_thp_page(),the boolean indicates whether to put_page(). IMHO, it might be too complicated to add an extra boolean to indicate whether to put_page(). It might be more straightforward to always put_page outside try_to_split_thp_page? Thanks. .