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Date: Thu, 27 Nov 2014 09:39:56 +0800
From: Miao Xie <miaox@cn.fujitsu.com>
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To: Chris Mason <clm@fb.com>
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Subject: Re: [PATCH v3 10/11] Btrfs: fix possible deadlock caused by pending
 I/O in plug list
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On Wed, 26 Nov 2014 10:02:23 -0500, Chris Mason wrote:
> On Wed, Nov 26, 2014 at 8:04 AM, Miao Xie <miaox@cn.fujitsu.com> wrote:
>> The increase/decrease of bio counter is on the I/O path, so we should
>> use io_schedule() instead of schedule(), or the deadlock might be
>> triggered by the pending I/O in the plug list. io_schedule() can help
>> us because it will flush all the pending I/O before the task is going
>> to sleep.
> 
> Can you please describe this deadlock in more detail?  schedule() also triggers
> a flush of the plug list, and if that's no longer sufficient we can run into other
> problems (especially with preemption on).

Sorry for my miss. I forgot to check the current implementation of schedule(), which flushes the plug list unconditionally. Please ignore this patch.

Thanks
Miao

> 
> -chris
> 
>