From: Wei Yang <richardw.yang@linux.intel.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Wei Yang <richardw.yang@linux.intel.com>,
hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com,
akpm@linux-foundation.org, cgroups@vger.kernel.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kirill.shutemov@linux.intel.com, yang.shi@linux.alibaba.com,
alexander.duyck@gmail.com, rientjes@google.com
Subject: Re: [Patch v2] mm: thp: grab the lock before manipulation defer list
Date: Mon, 13 Jan 2020 08:44:57 +0800 [thread overview]
Message-ID: <20200113004457.GA27762@richard> (raw)
In-Reply-To: <20200112225718.5vqzezfclacujyx3@box>
On Mon, Jan 13, 2020 at 01:57:18AM +0300, Kirill A. Shutemov wrote:
>On Sun, Jan 12, 2020 at 10:28:58AM +0800, Wei Yang wrote:
>> On Sat, Jan 11, 2020 at 03:03:52AM +0300, Kirill A. Shutemov wrote:
>> >On Thu, Jan 09, 2020 at 10:30:54PM +0800, Wei Yang wrote:
>> >> As all the other places, we grab the lock before manipulate the defer list.
>> >> Current implementation may face a race condition.
>> >>
>> >> For example, the potential race would be:
>> >>
>> >> CPU1 CPU2
>> >> mem_cgroup_move_account split_huge_page_to_list
>> >> !list_empty
>> >> lock
>> >> !list_empty
>> >> list_del
>> >> unlock
>> >> lock
>> >> # !list_empty might not hold anymore
>> >> list_del_init
>> >> unlock
>> >
>> >I don't think this particular race is possible. Both parties take page
>> >lock before messing with deferred queue, but anytway:
>>
>> I am afraid not. Page lock is per page, while defer queue is per pgdate or
>> memcg.
>>
>> It is possible two page in the same pgdate or memcg grab page lock
>> respectively and then access the same defer queue concurrently.
>
>Look closer on the list_empty() argument. It's list_head local to the
>page. Too different pages can be handled in parallel without any problem
>in this particular scenario. As long as we as we modify it under the lock.
>
>Said that, page lock here was somewhat accidential and I still belive we
>need to move the check under the lock anyway.
>
If my understanding is correct, you agree with my statement?
>--
> Kirill A. Shutemov
--
Wei Yang
Help you, Help me
next prev parent reply other threads:[~2020-01-13 0:45 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-09 14:30 Wei Yang
2020-01-09 18:52 ` David Rientjes
2020-01-09 18:58 ` Michal Hocko
2020-01-11 0:03 ` Kirill A. Shutemov
2020-01-12 2:28 ` Wei Yang
2020-01-12 22:57 ` Kirill A. Shutemov
2020-01-13 0:44 ` Wei Yang [this message]
2020-01-13 7:36 ` Kirill A. Shutemov
2020-01-13 8:23 ` Wei Yang
2020-01-14 9:31 ` Michal Hocko
2020-01-14 10:31 ` Kirill A. Shutemov
2020-01-14 10:59 ` Kirill A. Shutemov
2020-01-14 20:57 ` David Rientjes
2020-01-15 1:19 ` Wei Yang
2020-01-15 1:07 ` Wei Yang
2020-01-15 3:26 ` David Rientjes
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