Re: [Qemu-block] [Qemu-devel] [PATCH 3/3] linux-aio: fix re-entrant completion processing

[Roman Penyaev]

On Wed, Sep 28, 2016 at 5:01 AM, Fam Zheng <address@hidden> wrote:
> On Tue, 09/27 19:55, Roman Penyaev wrote:
>> > The bug is 100% deterministic.  Just boot up a guest with -drive
>> > format=qcow2,aio=native.
>>
>> It turns out to be that everything is broken.  I started all my
>> tests with format=raw,aio=native and immediately got coroutine
>> recursive.  That is completely weird.
>>
>> So, what I did is the following:
>>
>> 1. Took latest master (nothing works)
>> 2. Did interactive rebase to 12c8720
>> 12c8720 2016-06-28 | Merge remote-tracking branch
>> 'remotes/stefanha/tags/block-pull-request' into staging [Peter
>> Maydell]
>>
>> this merge request includes all your patches related to
>> virtio-blk and MQ support.
>>
>> 3. Applied 0ed93d84edab. Everything works fine.
>
> Have you tried qcow2 at this point? raw crashes with 1a62d0accdf85 doesn't 
> mean
> qcow2 is fine without it.
>

That's true.  qcow2 IO path is different, and presence of the
patch 1a62d0accdf85 does not affect - coroutine still enters
recursively.

But for me it is quite surprising that IO fragmentation (what
was done in 1a62d0accdf85) rises the misbehavior on raw IO path.

But of course originally issue was introduced by me.  Stefan,
thanks for a fix.

--
Roman