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

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Date:   Thu, 27 Sep 2018 16:53:06 +0100
From:   Eddie Chapman <eddie@...k.net>
To:     Coly Li <colyli@...e.de>, guoju <fangguoju@...il.com>
Cc:     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 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?

thanks,
Eddie