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Re: [Qemu-block] [PATCH] qed: fix bdrv_qed_drain
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-block] [PATCH] qed: fix bdrv_qed_drain |
Date: |
Tue, 23 Feb 2016 11:43:55 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 |
On 23/02/2016 06:57, Fam Zheng wrote:
>>>> + qed_cancel_need_check_timer(s);
>>>> + qed_need_check_timer_cb(s);
>>>> + }
>>>
>>> What if an allocating write is queued (the else branch case)? Its completion
>>> will be in bdrv_drain and it could arm the need_check_timer which is wrong.
>>>
>>> We need to drain the allocating_write_reqs queue before checking the timer.
>>
>> You're right, but how? That's what bdrv_drain(bs) does, it's a
>> chicken-and-egg problem.
>
> Maybe use an aio_poll loop before the if?
That would not change the fact that you're reimplementing bdrv_drain
inside bdrv_qed_drain.
Perhaps for now it's simplest to just remove the QED .bdrv_drain
callback, if you think this patch is not a good stopgap measure to avoid
the segmentation faults.
Once the bdrv_drain rework is in, we can move the callback _after_ I/O
is drained on bs and before it is drained on bs->file->bs.
Paolo