linux-kernel - Re: [PATCH 1/1] kasan: fix livelock in qlist_move

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Message-ID: <CACT4Y+aRGC9vVaHCXmeEiL5ywjQRTK+yNn+TAWKPLB3Gpd4U_A@mail.gmail.com>
Date:   Tue, 28 Nov 2017 18:57:41 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Zhouyi Zhou <zhouzhouyi@...il.com>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux-MM <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] kasan: fix livelock in qlist_move_cache

On Tue, Nov 28, 2017 at 6:56 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Tue, Nov 28, 2017 at 12:30 PM, Zhouyi Zhou <zhouzhouyi@...il.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.