linux-kernel - Re: [PATCH 5/9] blk-mq: don't set data->ctx and data->hctx in blk_mq_alloc_request

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Message-ID: <20200520030424.GI416136@T590>
Date:   Wed, 20 May 2020 11:04:24 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>, linux-block@...r.kernel.org,
        John Garry <john.garry@...wei.com>,
        Bart Van Assche <bvanassche@....org>,
        Hannes Reinecke <hare@...e.com>
Subject: Re: [PATCH 5/9] blk-mq: don't set data->ctx and data->hctx in
 blk_mq_alloc_request_hctx

On Wed, May 20, 2020 at 09:18:23AM +0800, Ming Lei wrote:
> On Tue, May 19, 2020 at 05:30:00PM +0200, Christoph Hellwig wrote:
> > On Tue, May 19, 2020 at 09:54:20AM +0800, Ming Lei wrote:
> > > As Thomas clarified, workqueue hasn't such issue any more, and only other
> > > per CPU kthreads can run until the CPU clears the online bit.
> > > 
> > > So the question is if IO can be submitted from such kernel context?
> > 
> > What other per-CPU kthreads even exist?
> 
> I don't know, so expose to wider audiences.

One user is io uring with IORING_SETUP_SQPOLL & IORING_SETUP_SQ_AFF, see
io_sq_offload_start(), and it is a IO submission kthread.

Thanks,
Ming