Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 20 May 2020 11:04:24 +0800
From:   Ming Lei <ming.lei@redhat.com>
To:     Christoph Hellwig <hch@lst.de>, linux-kernel@vger.kernel.org
Cc:     Thomas Gleixner <tglx@linutronix.de>, linux-block@vger.kernel.org,
        John Garry <john.garry@huawei.com>,
        Bart Van Assche <bvanassche@acm.org>,
        Hannes Reinecke <hare@suse.com>
Subject: Re: [PATCH 5/9] blk-mq: don't set data->ctx and data->hctx in
 blk_mq_alloc_request_hctx
Message-ID: <20200520030424.GI416136@T590>
References: <20200518093155.GB35380@T590>
 <87imgty15d.fsf@nanos.tec.linutronix.de>
 <20200518115454.GA46364@T590>
 <20200518131634.GA645@lst.de>
 <20200518141107.GA50374@T590>
 <20200518165619.GA17465@lst.de>
 <20200519015420.GA70957@T590>
 <20200519153000.GB22286@lst.de>
 <20200520011823.GA415158@T590>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200520011823.GA415158@T590>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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