From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E23FF56757 for ; Fri, 10 May 2024 02:59:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715309991; cv=none; b=AJXE2+FFfHDxMuVMWDPJtEyAHjx+cECsGCIVpjLi3lGcuzFS1s+qqPE+m8vJvmsN7xptCFDnQWcNDafgOP8x0EhS3YkjVm6vlWHOve/M717OguMl0Kt5g3VODdnTOnbslF///Vu6D2u2QZJMsHrBwzC69WUkqVeDs8pgV1RvVNc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715309991; c=relaxed/simple; bh=E35cDS4QnQB/w8COj0/DibA2uyG84mOHHN09JXoYD84=; h=Subject:To:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=VirX1iyYo2AwU7XJQQ3bXUyvudAAgLKggsWZdR7lU6FcKtg45Usf9nh+/6m71c1D+fyGMlP4G0h+EcRQXMnb09fbphaMG7nRF68EH0DeGVRZHhQ1+t7runCvBoogi9yG5NvzaxPNaPTxC0DSx1IHagkEjq+1vg5tXXG3n2TkoD8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.188 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.163.174]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4VbD8z6YMKzCrR4; Fri, 10 May 2024 10:58:27 +0800 (CST) Received: from canpemm500002.china.huawei.com (unknown [7.192.104.244]) by mail.maildlp.com (Postfix) with ESMTPS id C64A014038F; Fri, 10 May 2024 10:59:39 +0800 (CST) Received: from [10.173.135.154] (10.173.135.154) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2507.35; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To canpemm500002.china.huawei.com (7.192.104.244) 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. .