linux-kernel - Re: Spurious EIO on AIO+DIO+RWF

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Message-ID: <20181210124823.iw4mxmdqpsdfeap4@merlin>
Date:   Mon, 10 Dec 2018 06:48:23 -0600
From:   Goldwyn Rodrigues <rgoldwyn@...e.de>
To:     Avi Kivity <avi@...lladb.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>, linux-aio@...ck.org
Subject: Re: Spurious EIO on AIO+DIO+RWF_NOWAIT

On 13:19 09/12, Avi Kivity wrote:
> I have an application that receives spurious EIO when running with
> RWF_NOWAIT enabled. Removing RWF_NOWAIT causes those EIOs to disappear. The
> application uses AIO+DIO, and errors were seen on both xfs and ext4.
> 
> 
> I suspect the following code:
> 
> 
> /*
>  * Process one completed BIO.  No locks are held.
>  */
> static blk_status_t dio_bio_complete(struct dio *dio, struct bio *bio)
> {
>         struct bio_vec *bvec;
>         unsigned i;
>         blk_status_t err = bio->bi_status;
> 
>         if (err) {
>                 if (err == BLK_STS_AGAIN && (bio->bi_opf & REQ_NOWAIT))
>                         dio->io_error = -EAGAIN;
>                 else
>                         dio->io_error = -EIO;
>         }
> 
> Could it be that REQ_NOWAIT was dropped from bio->bi_opf? or that
> bio->bi_status got changed along the way?
> 

I don't think REQ_NOWAIT is dropped. I am assuming bio->bi_status error
is set differently. Is the blk queue being stopped? Is it possible to
instrument the kernel in your testcase?

-- 
Goldwyn