From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) (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 81FE73EA72 for ; Thu, 9 May 2024 08:30:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.255 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715243424; cv=none; b=rOEwMPAaQU2UjR8F3DIdTY6yl9ftfrgAbudwRcIvoXM3yIl/UMGF0yNuaY55tnPubiVseqxK+9PSfvJ6IavOvRYMdURZqqj7XjxJHGDQugXolLuINX8zfe1nIp190uKuwc6QyzVwIZgxl+/v1u7DDmNsGAdpOivFYbtwFx1pOf8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715243424; c=relaxed/simple; bh=C328mu3ZLLaMoY86QHm4QsC2s9qDJqQwWW5EVTHPZEQ=; h=Subject:To:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=WkA7I8S5qVuhdCgzGYbq/joXnSQsbpR+m7n6Ky4vtgxJfD9ko9j38E9NtYmHkUkMrHsy+S34rc9bEK61V7z0H/XZJBrACUD0DmI/rwnAGSbTHFIFfpEucQHoD2eisl1lL1l2e4OpedYjoI2JhNKoETJjVBX79m4zKMr+ZZOcgtk= 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=45.249.212.255 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 [172.19.163.48]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4VZlVR4S05z1RDD8; Thu, 9 May 2024 16:26:55 +0800 (CST) Received: from canpemm500002.china.huawei.com (unknown [7.192.104.244]) by mail.maildlp.com (Postfix) with ESMTPS id 9962A180032; Thu, 9 May 2024 16:30:16 +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; Thu, 9 May 2024 16:30:16 +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> From: Miaohe Lin Message-ID: <30d4d249-e3b1-79d5-3501-0ccb9c529110@huawei.com> Date: Thu, 9 May 2024 16:30:15 +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: <1b4c50b6-2371-4e1b-aef3-d70c32888054@oracle.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To canpemm500002.china.huawei.com (7.192.104.244) 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. > >> >>> I will revise the code so that put_page() is called regardless MF_ACTION_REQUIRED is set or not. >>> >>>>> + >>>> action_result is missing? >>> Indeed,  action_result() isn't always called, referring to the re-accessing hwpoison scenarios. >>> >>> In this case, I think the reason  is that, we just killed the process and there is nothing >>> >>> else to do or to report. >>> >>>>> +    return res; >>>>> +} >>>>> + >>>>>    /** >>>>>     * memory_failure - Handle memory failure of a page. >>>>>     * @pfn: Page Number of the corrupted page >>>>> @@ -2297,6 +2328,11 @@ int memory_failure(unsigned long pfn, int flags) >>>>>             */ >>>>>            SetPageHasHWPoisoned(hpage); >>>>>            if (try_to_split_thp_page(p) < 0) { >>>> Should hwpoison_filter() be called in this case? >>> Yes, it should. I will add the hwpoison_filter check. >>>>> +            if (flags & MF_ACTION_REQUIRED) { >> Only in MF_ACTION_REQUIRED case, SIGBUS is sent to processes when thp split failed. Any reson under it? > > I took a clue from kill_accessing_process() which is invoked only if MF_ACTION_REQUIRED is set. > > The usual code path for delivery signal is > > if page-is-dirty or MF_MUST_KILL-is-set or umap-failed, then > > - send SIGKILL if vaddr is -EFAULT > > - send SIGBUS with BUS_MCEERR_AR if MF_ACTION_REQUIRED is set > > - send SIGBUS with BUS_MCEERR_AO if MF_ACTION_REQUIRED is not set and process elected for MCE-early-kill > > So, if kill_procs_now() is invoked only if MF_ACTION_REQUIRED (as it is in the patch), one can argue that > > the MCE-early-kill request is not honored which deviates from the existing behavior. > > Perhaps I should remove the > > + if (flags & MF_ACTION_REQUIRED) { I tend to agree MCE-early-kill request should be honored when try to kill process. Thanks. .