Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
In-Reply-To: <CACT4Y+aRGC9vVaHCXmeEiL5ywjQRTK+yNn+TAWKPLB3Gpd4U_A@mail.gmail.com>
References: <1511841842-3786-1-git-send-email-zhouzhouyi@gmail.com>
 <CAABZP2zEup53ZcNKOEUEMx_aRMLONZdYCLd7s5J4DLTccPxC-A@mail.gmail.com>
 <CACT4Y+YE5POWUoDj2sUv2NDKeimTRyxCpg1yd7VpZnqeYJ+Qcg@mail.gmail.com>
 <CAABZP2zB8vKswQXicYq5r8iNOKz21CRyw1cUiB2s9O+ZMb+JvQ@mail.gmail.com>
 <CACT4Y+YkVbkwAm0h7UJH08woiohJT9EYObhxpE33dP0A4agtkw@mail.gmail.com>
 <CAABZP2zjoSDTNkn_qMqi+NCHOzzQZSj-LvfCjPy_tg-FZeUWZg@mail.gmail.com>
 <CACT4Y+ah6q-xoakyPL7v-+Knp8ZaFbnRRk_Ki6Wsmz3C8Pe8XQ@mail.gmail.com>
 <CAABZP2yS524XEiyu=kkVx7ff1ySTtE=WWETNDrZ_toEm0mwqyQ@mail.gmail.com>
 <CACT4Y+aAhHSW=qBFLy7S1wWLsJsjW83y8uC4nQy0N9Hf8HoMKQ@mail.gmail.com>
 <CAABZP2wxDxAHJ_f022Ha7gyffukgo0PPOv2uJQphwFXGO_fL1w@mail.gmail.com>
 <CACT4Y+bprRRzTD5DjSTZt8oobhYcD-eTOT_VwWwcTZBhRH1KUg@mail.gmail.com> <CACT4Y+aRGC9vVaHCXmeEiL5ywjQRTK+yNn+TAWKPLB3Gpd4U_A@mail.gmail.com>
From:   Zhouyi Zhou <zhouzhouyi@gmail.com>
Date:   Wed, 29 Nov 2017 07:41:12 +0800
Message-ID: <CAABZP2xDmOT8-=eqjVF6dFAcJ2SZesX4CsJ7gmqGjHjsTXdt0w@mail.gmail.com>
Subject: Re: [PATCH 1/1] kasan: fix livelock in qlist_move_cache
To:     Dmitry Vyukov <dvyukov@google.com>
Cc:     Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux-MM <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi,
    I will try to reestablish the environment, and design proof of
concept of experiment.
Cheers

On Wed, Nov 29, 2017 at 1:57 AM, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Tue, Nov 28, 2017 at 6:56 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
>> On Tue, Nov 28, 2017 at 12:30 PM, Zhouyi Zhou <zhouzhouyi@gmail.com> wrote:
>>> Hi,
>>>    By using perf top, qlist_move_cache occupies 100% cpu did really
>>> happen in my environment yesterday, or I
>>> won't notice the kasan code.
>>>    Currently I have difficulty to let it reappear because the frontend
>>> guy modified some user mode code.
>>>    I can repeat again and again now is
>>> kgdb_breakpoint () at kernel/debug/debug_core.c:1073
>>> 1073 wmb(); /* Sync point after breakpoint */
>>> (gdb) p quarantine_batch_size
>>> $1 = 3601946
>>>    And by instrument code, maximum
>>> global_quarantine[quarantine_tail].bytes reached is 6618208.
>>
>> On second thought, size does not matter too much because there can be
>> large objects. Quarantine always quantize by objects, we can't part of
>> an object into one batch, and another part of the object into another
>> object. But it's not a problem, because overhead per objects is O(1).
>> We can push a single 4MB object and overflow target size by 4MB and
>> that will be fine.
>> Either way, 6MB is not terribly much too. Should take milliseconds to process.
>>
>>
>>
>>
>>>    I do think drain quarantine right in quarantine_put is a better
>>> place to drain because cache_free is fine in
>>> that context. I am willing do it if you think it is convenient :-)
>
>
> Andrey, do you know of any problems with draining quarantine in push?
> Do you have any objections?
>
> But it's still not completely clear to me what problem we are solving.

From 1585333592996552869@xxx Tue Nov 28 17:58:50 +0000 2017
X-GM-THRID: 1585281151451498932
X-Gmail-Labels: Inbox,Category Forums,HistoricalUnread