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Date:   Wed, 13 Apr 2022 09:51:13 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
        Changhui Zhong <czhong@redhat.com>
Subject: Re: [PATCH] block: avoid io timeout in case of sync polled dio
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On Wed, Apr 13, 2022 at 04:48:05PM +0800, Ming Lei wrote:
> If the bio is marked as POLLED after submission,

Umm, a bio should never be marked POLLED after submission.

> bio_poll() should be
> called for reaping io since there isn't irq for completing the request,
> so we can't call into blk_io_schedule() in case that bio_poll() returns
> zero.
> 
> Also for calling bio_poll(), current->plug has to be flushed out,
> otherwise bio may not be issued to driver, and ->bi_cookie won't
> be set.

I think we just need to bypass the plug to start with for synchronous
polled I/O. 

Do you have a reproducer?  We'd also need to sort all this out for
polled file system I/O as well.