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

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Date:   Sun, 9 Dec 2018 13:19:51 +0200
From:   Avi Kivity <avi@...lladb.com>
To:     linux-kernel <linux-kernel@...r.kernel.org>, linux-aio@...ck.org,
        Goldwyn Rodrigues <rgoldwyn@...e.de>
Subject: Spurious EIO on AIO+DIO+RWF_NOWAIT

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?

Reducing the test case may be a lot of work, but I can package a binary 
using docker if a reproducer is needed. Seen on 4.18.19 and 4.19.something.