linux-kernel - Re: [PATCH 4.19 078/361] nvmet-rdma: use a private workqueue for delete

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Message-ID: <a90c8564-3b8a-0c75-4a2e-bf497072f849@acm.org>
Date:   Sun, 11 Nov 2018 17:27:05 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org, Sagi Grimberg <sagi@...mberg.me>,
        Christoph Hellwig <hch@....de>, Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 078/361] nvmet-rdma: use a private workqueue for
 delete

On 11/11/18 2:17 PM, Greg Kroah-Hartman wrote:
> 4.19-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Sagi Grimberg <sagi@...mberg.me>
> 
> [ Upstream commit 2acf70ade79d26b97611a8df52eb22aa33814cd4 ]
> 
> Queue deletion is done asynchronous when the last reference on the queue
> is dropped.  Thus, in order to make sure we don't over allocate under a
> connect/disconnect storm, we let queue deletion complete before making
> forward progress.
> 
> However, given that we flush the system_wq from rdma_cm context which
> runs from a workqueue context, we can have a circular locking complaint
> [1]. Fix that by using a private workqueue for queue deletion.

Hi Greg,

You may want to drop this patch. A bug was discovered in this patch a 
few days ago. I think not backporting this patch is better than 
backporting it. See also the discussion at 
http://lists.infradead.org/pipermail/linux-nvme/2018-November/020766.html. 
A quote from that e-mail thread: "I think we need to revert 2acf70a 
("nvmet-rdma: use a private workqueue for delete") altogether because it 
never made any difference..".

Bart.