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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
References: <154322517208.18737.3297786654135648324.stgit@localhost.localdomain>
 <00b1782a-5c5c-5bc8-7ea9-4f8450679fa1@virtuozzo.com>
 <CAJfpeguokUoCPEnK7Q_Rp9cmyBCMfm51=7TmbbS-QiEy2BxxAQ@mail.gmail.com>
 <a45d54a3-b275-9c95-3c9d-a19566e447dc@virtuozzo.com>
 <CAJfpegvOgA+Wd3vTRqYQP7p_SJ11YCffquP_R=WRHwqYD4b=Ng@mail.gmail.com>
From:   Kirill Tkhai <ktkhai@virtuozzo.com>
Message-ID: <b198f480-9ce7-9663-40b1-193a05846c95@virtuozzo.com>
Date:   Tue, 15 Jan 2019 18:55:21 +0300
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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.

>See fuse.git#for-next.

The renewed patch looks correct for me.

Thanks,
Kirill