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Subject: Re: [PATCH 1/2] fuse: Fix race in fuse_writepage_in_flight()
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
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From:   Kirill Tkhai <ktkhai@virtuozzo.com>
Message-ID: <66761b4e-dcdb-1a73-ceca-0eebebaaa289@virtuozzo.com>
Date:   Tue, 15 Jan 2019 19:05:12 +0300
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On 15.01.2019 19:03, Miklos Szeredi wrote:
> On Tue, Jan 15, 2019 at 4:55 PM Kirill Tkhai <ktkhai@virtuozzo.com> wrote:
>>
>> On 15.01.2019 18:37, Miklos Szeredi wrote:
>>> On Thu, Jan 10, 2019 at 12:03 PM Kirill Tkhai <ktkhai@virtuozzo.com> wrote:
>>>>
>>>> On 10.01.2019 14:00, Miklos Szeredi wrote:
>>>>> On Thu, Jan 10, 2019 at 11:48 AM Kirill Tkhai <ktkhai@virtuozzo.com> wrote:
>>>>>>
>>>>>> Hi, Miklos,
>>>>>>
>>>>>> any comments about this?
>>>>>
>>>>> Is there a reproducer?  ISTR that fsx-linux with mmaps enabled was
>>>>> good for stressing the writeback_cache code.
>>>>
>>>> There is no a reproducer, since I found that by eyes during preparation of another patchset.
>>>
>>> That's good.  It would even better to have a reproducer, but it
>>> doesn't look easy...
>>>
>>> Completely redid this and reordered the patchset so this change is
>>> made before the locking changes actually introduce the bug.
>>
>> Hm, I meant that I found this during preparation of the patchset,
>> but not that fi->lock patchset introduces the bug. I don't think
>> the patchset is involved:
>>
>> 1)before we had race, because different locks fc->lock and fiq->waitq.lock
>> are taken in fuse_dev_read() and fuse_writepage_in_flight();
>> 2)after we have the same race, and the locks are fi->lock and fiq->waitq.lock.
> 
> Ah, so the race was introduced earlier, when fiq->waitq.lock was split
> out from fc->lock.

Yeah, and there was another performer, not me :)