From: Ding Hui <dinghui@sangfor.com.cn>
To: "HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@redhat.com>,
Oscar Salvador <osalvador@suse.de>,
Michal Hocko <mhocko@suse.com>, Tony Luck <tony.luck@intel.com>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v1 6/6] mm/hwpoison: fix unpoison_memory()
Date: Sat, 19 Jun 2021 20:22:32 +0800 [thread overview]
Message-ID: <a2162c28-78ce-1ce7-327c-e8c4dce164cd@sangfor.com.cn> (raw)
In-Reply-To: <20210618083625.GA2215283@hori.linux.bs1.fc.nec.co.jp>
On 2021/6/18 4:36 下午, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Thu, Jun 17, 2021 at 06:00:21PM +0800, Ding Hui wrote:
>> On 2021/6/14 10:12, Naoya Horiguchi wrote:
>>> From: Naoya Horiguchi <naoya.horiguchi@nec.com>
>>>
>>> After recent soft-offline rework, error pages can be taken off from
>>> buddy allocator, but the existing unpoison_memory() does not properly
>>> undo the operation. Moreover, due to the recent change on
>>> __get_hwpoison_page(), get_page_unless_zero() is hardly called for
>>> hwpoisoned pages. So __get_hwpoison_page() mostly returns zero (meaning
>>> to fail to grab page refcount) and unpoison just clears PG_hwpoison
>>> without releasing a refcount. That does not lead to a critical issue
>>> like kernel panic, but unpoisoned pages never get back to buddy (leaked
>>> permanently), which is not good.
>>
>> As I mention in [1], I'm not sure about the exactly meaning of "broken" in
>> unpoison_memory().
>>
>> Maybe the misunderstanding is:
>>
>> I think __get_hwpoison_page() mostly returns one for hwpoisoned page.
>> In 06be6ff3d2ec ("mm,hwpoison: rework soft offline for free pages"),
>> page_handle_poison() is introduced, it will add refcount for all
>> soft-offlineed hwpoison page.
>> In memory_failure() for hard-offline，page_ref_inc() called on free page
>> too, and for used page, we do not call put_page() after get_hwpoison_page()
>> != 0.
>> So all hwpoisoned page refcount must be great than zero when
>> unpoison_memory() if regardless of racy.
>
> Hi, Ding,
>
> Thanks for the comment. I feel that I failed to define the exact issue in
> unpoison. Maybe I saw and misinterpreted some random error as unpoison's
> issue during developing other hwpoison patches, so please don't take serious
> my previous wrong word "broken", sorry about that.
>
> Anyway I reconsider how to handle this 6/6, maybe it will be a clear
> description of the problem, and will be simplified.
>
>>
>> Recently I tested loop soft-offline random pages and unpoison them for days,
>> it works fine to me. (with bac9c6fa1f92 patched)
>
> Thank you for testing,
>
Hi Naoya,
I'm afraid of my description about testing is ambiguous for others, let
me clarify that I ran stress soft-offline test case from mce-test
project (https://git.kernel.org/pub/scm/utils/cpu/mce/mce-test.git) for
days to verify my modify about NR_FREE_PAGES (bac9c6fa1f92), without
your current patchset, the case is loop soft-offline random pages and
unpoison them, and it works basic fine to me.
--
Thanks,
-dinghui
prev parent reply other threads:[~2021-06-19 12:23 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-14 2:12 [PATCH v1 0/6] mm/hwpoison: fix unpoison_memory() Naoya Horiguchi
2021-06-14 2:12 ` [PATCH v1 1/6] mm/hwpoison: mf_mutex for soft offline and unpoison Naoya Horiguchi
2021-06-15 11:41 ` Ding Hui
2021-06-15 11:55 ` HORIGUCHI NAOYA(堀口 直也)
2021-06-15 12:42 ` Miaohe Lin
2021-06-16 0:41 ` HORIGUCHI NAOYA(堀口 直也)
2021-06-16 3:14 ` Miaohe Lin
2021-06-14 2:12 ` [PATCH v1 2/6] mm/hwpoison: remove race consideration Naoya Horiguchi
2021-06-15 12:57 ` Ding Hui
2021-06-16 0:11 ` HORIGUCHI NAOYA(堀口 直也)
2021-06-16 0:40 ` Ding Hui
2021-06-14 2:12 ` [PATCH v1 3/6] mm/hwpoison: introduce MF_MSG_PAGETABLE Naoya Horiguchi
2021-06-14 3:06 ` Matthew Wilcox
2021-06-14 3:55 ` HORIGUCHI NAOYA(堀口 直也)
2021-06-14 2:12 ` [PATCH v1 4/6] mm/hwpoison: remove MF_MSG_BUDDY_2ND and MF_MSG_POISONED_HUGE Naoya Horiguchi
2021-06-14 2:12 ` [PATCH v1 5/6] mm/hwpoison: make some kernel pages handlable Naoya Horiguchi
2021-07-28 10:59 ` Ding Hui
2021-07-29 6:54 ` HORIGUCHI NAOYA(堀口 直也)
2021-06-14 2:12 ` [PATCH v1 6/6] mm/hwpoison: fix unpoison_memory() Naoya Horiguchi
2021-06-17 10:00 ` Ding Hui
2021-06-18 8:36 ` HORIGUCHI NAOYA(堀口 直也)
2021-06-19 12:22 ` Ding Hui [this message]
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