linux-kernel - Re: [PATCH] bcache: add separate workqueue for journal

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Date:   Fri, 28 Sep 2018 10:32:53 +0800
From:   Coly Li <colyli@...e.de>
To:     Eddie Chapman <eddie@...k.net>
Cc:     guoju <fangguoju@...il.com>, kent.overstreet@...il.com,
        linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bcache: add separate workqueue for journal_write to avoid
 deadlock


On 9/27/18 11:53 PM, Eddie Chapman wrote:
> On 27/09/18 16:23, Coly Li wrote:
>>
>> On 9/27/18 9:45 PM, guoju wrote:
>>> After write SSD completed, bcache schedule journal_write work to
>>> system_wq, that is a public workqueue in system, without WQ_MEM_RECLAIM
>>> flag. system_wq is also a bound wq, and there may be no idle kworker on
>>> current processor. Creating a new kworker may unfortunately need to
>>> reclaim memory first, by shrinking cache and slab used by vfs, which
>>> depends on bcache device. That's a deadlock.
>>>
>>> This patch create a new workqueue for journal_write with WQ_MEM_RECLAIM
>>> flag. It's rescuer thread will work to avoid the deadlock.
>>>
>>> Signed-off-by: guoju <fangguoju@...il.com>
>>
>> Nice catch, this fix is quite important. I will try to submit to Jens 
>> ASAP.
>>
>> Thanks.
>>
>> Coly Li
>
> Once this goes into 4.19, would this be a candidate for backporting to 
> any stable kernels, or does it only fix something introduced in this 
> cycle?
>
This bug exists in upstream for quite long time, it should be applied to 
all stable kernels which it can be applied. And it is Cced to 
stable@...r.kernel.org already.

Coly Li